Matt I had an old guy framing a house for me years ago. The owner came by and kept on and on about several surface cracks in the slab. My framer got tired of listening to him, walked over and said "You tell me how to pour a slab without it cracking and you and I will never have to work another day in our life. He never said another thing about the cracks.
It is possible to avoid cracks but its hard to do. I did a mat slab 75cm, all rebar and self-consolidating and ponded for over a month and it never cracked - but maybe that was just lucky !
@@Kpopzoom by "ponded" do you mean kept moist? I've read that one of the primary reasons concrete cracks is shrinkage caused by drying too fast; and that keeping the slab covered with plastic allows it to cure much slower and avoids some cracking. It makes sense to me, but I have no practical experience.
@@scottcraig1047 By Ponded I mean a small dam is built all round the slab (in this case using the waterproof turned up) and the entire slab is filled with water to a depth of a few inches. The water is then kept topped up daily to maintain the slab effectively underwater for the entire curing period.
surface cracks mean nothing because you have rebar, but most homeowners aren't structural engineers or contractors and don't understand this, of course!
It’s pretty dull. There is just a calf sized electric tool that pulls on the cable. There are stories of a cable breaking and coming up through the concrete and whipping around. Sort of a rare event. Never saw that happen. Btw that slab has already been tensioned. The wedges are in
My 1970’s post tension slab saved our house! We live on a steep slope and our house started sinking. It was 5” out of level and not a crack in sight! It moved as a boat, as Matt described. A rebar slab would likely have broken. The remodel part is also an issue. We paid over $600 for someone to essentially bring in a giant fish finder X-ray contraption to map our cables ... and then you can only cut around them. I’ve been told they’re used a LOT in parking terraces and other commercial applications. Not sure how they impact load? Also: I was REALLY glad to hear Matt say he avoids running water supply lines under or through slabs!!!! In Southern California, this has caused SERIOUS ISSUES with plumbing leaks, particularly with copper pipes! I would NEVER run my supply lines under cement!!! If you haven’t had a slab leak here yet, be prepared because sadly, you will! It’s just a matter of when! Good episode!
In Phoenix, pretty much all new homes are post tension. House I just had built is a post tension, I prefer rebar slab because you can remodel and move plumbing around in the future. Post Tension, you are pretty much locked. The cables were not tensioned for about 6 months. The builder waited for the full framing to go up and they did it just before the stucco install. And not a single crack, even small shrinkage cracks, the slab turned out perfect.
big O because they cut off the tail after placing it under tension. If you released the tension - the cable would pull back into the slab never to be seen again.
I bought a house that had a post tension cable failure where 2 cables crossed near a perimeter wall. The failure probably occurred many years before I bought the house and it was difficult to diagnose the cause of the failure. My guess is that water got into the end of the cable because the recessed hole for the cable slips was not filled and sealed properly and corrosion occurred. When one cable broke the release of energy caused the other cable to break. There was a 12 inch crater in the slab. I watched the guys that did the repair and re- tensioning and it was fascinating how they were able to fish out the old cable and splice everything together.
I’ve seen builders treat the tension technology has some kind of magic that will overcome the basic laws of engineering and physics. If the slab is poured onto unprepared ground and you exert enough pressure/the weight of the house on one side, it’ll crack into several large pieces. One house I saw cracked and had sunk 4 inches on the backside of the slab, the house wasn’t even a year old. We dug down and found the builder had put the slab in contact with fill sand on the perimeter wall. He thought his magic tension system would allow him to forgo basic concrete work.
I always like your videos. I am retired now but spent my entire working life in the building industry engaged in the professional (architectural) side of things. In my country (Australia) we almost never do post tensioning on domestic ground slabs but it is used a lot on commercial projects where its main advantage is increased spans and hence wider spacing between columns. I really appreciate your videos and your commitment to building science. Some of what you do would be regarded as 'overkill' here but our climate is probably a little kinder than what you have.
Matt Risinger we have had really good success with the post tension on our engineered slabs which we use a lot on our Barndominium builds. But we also use rebar on occasion. The one we poured this week we used rebar with 12” spacing.
PT is very popular in the southwest, almost all slabs are PT. In my industry (ironworker) we do the post tension on the big commercial and bridge projects. PT is no joke I have witnessed the damage it can cause.
I believe that slab has been tensioned already. Look at the white spray paint lines on the cables . Those are the reference marks sprayed prior to stressing by the stressing crew immediately before they stress. The stressing crew, sprays the cable, stresses it; and then leaves the cables un-cut. Then, an inspector or engineer will come out and measure the cable elongation. The elongation (strain) is used to calculate the amount of stress the cable is under; and to make sure it is within design parameters. Once the inspector signs off on the proper cable stress; the stressing crew returns to the site to cut all the cables and grout the holes. ruclips.net/video/3UKh8vTpnrY/видео.html
Matt, the reason for the cracks in the slab is not the downward motion of the edges as you had described. You mentioned the reason in the name itself. It is shrinkage. Each and every little bit of concrete shrinks in all 3 dimensions. What causes the cracks is the addition of each bit of concrete to how much movement a given direction will experience. The length of this slab is longer than its width, as you said a rectangle, so the addition of all that length will add up to enough shrinkage movement/tension that a crack will occur perpendicular to that length. This is the reason sidewalks are scored with control joints in the short direction... as the long long direction is the one where tension will build up.
Matt, the use of PT systems for slab on grade is really surprising to me, and i'm not completely sure how it is supposed to be achieving any form of crack control to be honest. Typically the reason we use PT slabs is to control deflection (and as a result SOME of the cracking), so we end up basically inducing a "camber", thus the slab flattens once the dead and live loads make their way onto it, instead of deflecting, so the cracks that are prevented as a result of this, are typically the ones that you would notice on the underside of that slab, not the top. Let me say that i am not an engineer, but an architect, and certainly cannot claim to be an expert on this subject. Thanks for the video.
Not quite. Repairing pt cables is pretty straight forward. Open up the cable ends enough to grab hold of the cable ends. Where the cable has been cut, splicers, similiar to chinese money. Allows for the cable restretch.
Thank you so much for this video. We are building a brand new home and noticed hairline cracks like the ones in this video. But they are not higher than each other so don't believe they are structural foundation cracks. Thanks to your video, I can breath a sight of relief.
I am building a new home in AZ, and I have cracks in my Post-Tension slab. Your video has eased my mind that it's going to be OK.. Thank you so much for this video..
Its worth mentioning from a life safety side. I have been designing, installing and stressing thousands of slabs and a tradesman coming later that cuts a stressed tendon with 32kips of stored energy can kill. I have witnessed it in high rise decks. Only 3 days after stressing.
@@marcmyers1465 Its not very much. All the tendon stressed forces are "inside" the slab. Approximately 8-10" from face of concrete. Also, the concrete cover on the top of the tendons is more than adequate for tendon containment. Even at recessed patio areas. I would assume all the tendons are in a flat plane with very little drape. No the instance of reverse curvature blow out is very small. Interesting is the (3) tendons in a bunch. Even if this is for a bearing wall of surface mounted column I wouldn't place them that tightly grouped. It would be better to place them in flat plane 6" CC spacing. Lastly, then Ill shut up. The finish sealing on the tendon ends after cutting is very important ti use rust proofing sealer/paint and encapsulate the tendon ends with non-shrink, non-metallic grout. Thanks
Thanks, Matt, as always very informative. I've never been involved with building a post-tension slab so its really cool to get acquainted w/the process. I agree, pier & beam foundations have advantages and cost-saving potential, especially on steep terrain.
Was interesting to watch this. In the 70's I was walking through a house that was under construction. This house had already been framed and sold. The slab was on grade with post-tensioning. When I walked into the master bath, I noticed a scary thing. They had used a jackhammer to remove the slab where the bathtub was going to be placed. Right through the center of the hole running the long direction was a tensioning cable. I had to laugh and went to get my dad. He could not believe that they were even considering the remote possibility of cutting the cable to put in a sunken bathtub. Presently I live in a house with post-tensioning for the slab reinforcement. Sadly, after watching the builder construct homes near me, they did not wait for anything with the slab. The tensioning was done within 72 hours of the slab being poured. The framing was going up and the slabs were still green in color. The other builders in the area waited 28 or more days before framing the new homes.
Post tensioned slabs have been used on almost every home built in Arizona for the last 20 years. It has been used in commercial buildings for decades. Just sold a home 16 years old with zero cracks, including the garage. It is a fantastic way of building a slab on expansive soil which we have a lot of in Arizona.
he said those are braided cables, hes wrong, those are twisted cables with a twist every half inch, up to a twist every two inches. no one uses braided cables for construction, under tension they deform at the wire crossings. the most popular cable is two or three opposing twisted wire layers, (wire rope), an example, first layer clockwise, next layer counter clockwise, top layer clockwise. makes a strong cable that will puller uniformly without internal stress.
Most residential new construction slabs around the Phoenix metro since 2000 are post-tension slabs. We have clay soils here that swell and shrink with water absorption and loss. Post-tension slabs combat the moving soil. Great video!
Should have started tension as it was curing; and finished it after it cured... that would have prevented cracking on the slab. Thats what they do on commercial projects where a tensioner is onsite.
@@itech301 Only if done before the concrete is poured. xephael is suggesting a two-stage post tensioning. Sounds to me like the equivalent of pulling the forms on multi-story cast in place after a week, then immediately placing shore poles and beams to prevent deflection or cracking for the balance of the 30 days to "full" strength. The pole shores leave a lot of space for construction activities to proceed on that floor level, whereas the forming systems left in place mean one can't do anything on that floor until they are stripped.
Agree. Initial tension and final tension is better, typically at 3 days then again at 7-10 days after pouring. But to be fair that is probably quite costly for your standard house slab.
I suspect that slab has already been tensioned- frame at 2:38 shows swedge anchors in the pocket and white paint in the tail of the cable, which is typically done to measure stretch (strain) of the cable as tensioning. They just haven’t cut the tails off yet, or possibly left them to retension
Mat. I’m sure I’ll get no response out of this. But??? You pretty much explained how you fix a stretched pressure cable. You said that they are greased up pretty good so it’s easier to stretch them to ad the strength to the slab itself. On the opposite end of what you were showing is a snatch block. When you put the tensioner on then you were showing. But first cut that snatch block off. Then they actually make a sleeve that goes over the top of the cables. You weld this sleeve to both cables and start pulling. You can pull the old cable out while you are pulling the new cable in. If you have a cut or broken cable let’s say where the apprentice hit it with a jack hammer. You must clean the cable where it was broken and splice it back together so the complete cable can be removed and the new cable can be drawn it. Once it is in. You cut it at the far end. Put a new tension plate on the end. Draw it back down tight. Now that’s a long Paragraph
Wow. I didn't know about the danger of jackhammering the cement around those cables. I have a post tension slab and I had a collapsed drain line in my washroom. I did a remodel and moved the sewer and water lines. I hit those cables and ripped the plastic of of them. they didn't break and it is covered back up now with 4500 PSI cement and then tile. Thanks for the info.
Probably could have made a 2 minute video of this if you just said it was cheaper in the beginning. The cheaper it is the more it will be defended or pitched as better by contractors looking to maximize profit. Would be curious to see how much cheaper the labor end of it is too, including the rental (if needed) of the machine that does the tensioning.
Hey matt I love watching your videos they are very educational. I live up in mass. And like learning how different things are in the south. Also love learning things cuz people can take anything from you but not your knowledge...keep up the videos...by the way do you sell those build hats? Would love to get one
Should be tensioned within 72 hours and kept most that will reduce the shrinkage cracks. I do special inspection on this type of construction as well as many other types of concrete construction.
Interesting. I'm a concrete pump operator from NW FL. I've never seen tension cables on a house slab. Most around here are done with rebar footers/grade beams, then use wire remesh sheets or rolls. Very rarely do I see rebar mat slabs either. It's sometimes used on wetlands or on the sandy beach. Stem wall foundations are most common around here.
The tendons have been painted and the paint is 6 or so inches away from the concrete. They've already been tensioned. Typically we tension the morning of the second day after placing concrete. If you wait 7 to day days the concrete cures too much. Engineers typically require it be tensioned within 72 hours.
Home Inspector here. I know of a very unhappy construction site manager who is upset because he was called out by someone ...... 6weeks after pouring the slab, it has still not been tensioned. There is now a crack down the center varying in width. They have a staff-paid Structural Engineer coming out to verify everything is 'ok'.
I was doing a commercial job and I was in the dining area when I heard the cable get cut. Very recognizable sound and I was standing right on top of it. The guys outside trimming off part of the foundation cut right through it with the gas saw...
Would love to see a guided tour of a concrete slab or other job that uses twisted micro rebar (helix) as its primary reinforcement! It would look to be right up your ally.
In south Louisiana we don’t have the expansive clays instead we have nothing but river silt to build on so there is nothing solid to build on. Consequently, I advocate for post tension.
Matt, I have a question about the BuildApp webpage. Seems like all the videos I've watched have an issue with the audio syncing can you correct that problem?
I was in a 20 story hi rise and one on the guys on a crew hit the tension wore on the core tower on a almost finish building. It was so loud and freaked everybody out as the building shook and it took almost a year to fix it.. UUUG is was so bad. Always ask before you drill!!
I just made a comment on these types of slabs should come with a map with exact measurements to stop or at least reduce the chance of hitting/cutting one.
august they do. Check out the PT shop drawings. You’ll get extremely close with them so long as they didn’t need to adjust or move anything in the field.
I would like to see about the different ways to build a basement on a new construction house and then how if possible to build a basement in a pre-existing concrete slab house
Other than cost, what would be the disadvantages (and advantages) of doing both rebar and post tension in combination? Is there ever a time you would do both together?
Wonder if/when glass fiber reinforced or basalt fiber reinforced rebar will come down in price to become cheaper than steel rebar? I think Owens Corning's "pink bar" or Aslan 100 fiberglass rebar may now cost about the same as steel.
At 3:18 of the video, the tendon has been tensioned and the two half- circle wedges have been "seated." They are waiting to be cut after city inspector signs off.
Had to have two cables replaced on my slab since the foundation lifting company snapped a few jack hammering through my garage floor. They had to pay for the repair since I told them about the cables and said they would scan to avoid them but the crew did not even when I reminded them.
The soils where I live are mostly very stable, so 4" thick concrete is typical for slab on grade, and no reinforcing is put in except in the toe at the perimeter. We did do one job, however, that was in an area of town that has expansive clay. That one got a 12" thick slab with 2 layers of #6 bars at 24" O.C. both ways. It did not get a perimeter toe, the slab itself was considered by the engineer to be strong enough to resist any uneven shifting. That seems a bit over optimistic to me, especially considering the enormous size of that place, but the engineer put his stamp on it, so he owns it.
I miss doing Construction It Was A Talent Of Mental Science I Was Blessed To Work On 100 Million Dollar Projects To A 200.00 Sheetrock job Learning Everything Is A Blessing Being Mechanically Incline Is The Greatest Gift Because When Everything Falls We Build It Back Or Something New 👷♂️👊🏽💯
Hey Matt you mentioned that you don't like to bring water supply lines in thru the slab - can you show some details about how you bring them into the home?
My current house is post tention. Still have the hairline cracks and it was done 38 years ago. I'm afraid to tear up hallway flooring because I know there's an issue. Just have no clue how severe it is. Right side is off by 3/8 inch but the left is off by 1 inch. Walls on the 3/8 side have some splitting where tape and float was done on corners of 1 wall and under 1 window. Have to do some grading on the left side as last owner was an idiot and built up the ground by 2 inches so water flows toward house. Also installing rain gutters to direct water away from effected areas.
In the uk we use black and bean foundation that means there’s an empty void under the house until you get to your highest point of the hill. From there you build a regular house from the flat surface from the blocks (concrete slabs) and beams (concrete beams just like steel beams in warehouses). The void foundation has some special bricks spread throughout to help let gasses out. This is my favourite building style
@Matt Risinger what about using alternative materials for reinforcing the concrete, fibers polymers materials in alternative from steel? The question being durability and corrosion. Maybe a video on that
A coworker built a home with this system but the concrete was stamped then stained. Sounded like a substantial cost savings, compared to the NE where a slab home would be a tough sale. Most everyone expects below grade living space.
When remodeling and cutting a post tensioned slab, we locate the cables and mark them so we know where to cut the slab. Update your video to include this information.
Hi guys, notice: * plastic on foundation under steel. * when site security fences not required all steel ends capped. * barriers for sub terrarium termites, especially collars around plumbing. * new testing on permeability of water in concrete to reduce spalling.🔎💡
How do you put the wall on the anchor bolt? Do you have to put bottom plate first and then put the rest of the wall on? Or you build the wall on the ground and then lift the wall into the anchor bolt?
Good vid once again. On a side observation, I bet Matt is regretting black as the official "Build" color as we get into these summer months. The difference in a light color vs dark is tremendous when you're out in the sun.
Many tract builders in expansive soil areas will use post tension to minimize liability for slab shifting and structural damage. I’ve seen a number of garage floors with warnings about sawcutting and the danger caused by snapping a tensioned cable. YIKES!
Matt, I have a typical track home in southern California and I am going to update the floors on the second story. How would you remedy the sound transmission? I am thinking some thick Advantec with screws and some form of adhesive.
Hello Matt. I'm curious in what your job description is. And if possible how you got there. I have my own construction business and I would love to expand, mainly because I would prefer to do the planning rather than the execution. I'm just getting worn down, cuz I'm my own employee, and on top of that I run alot as well. I'm just wondering if I can stay in construction yet "move up" to possibly earn more money and help build or repair more homes. Thank you, have a great day.
Interesting video. Why is that foundation so darn high? It's about 3 feet higher than the existing houses in the neighborhood, and the house is going to stick out like a sore thumb. I'm a little confused how pulling the rods will cause them to push more tightly against the concrete. Are you sure they don't twist them more to tighten them? Someone told me once that the slab on my house is post tension but I'm kind of skeptical.
Hi Matt! So I have a quick question in regards to post-tension foundations - Our new home in your area has a post-tension foundation as well as soil injections to the whole lot. What do you think of soil injections? Do you think they help? Thanks!
Matt I live in Killeen Texas. My home is a single story 3600sf with a spray foam attic. I have two 3.5 ton air conditioners. Will an 1850 Aprilaire dehumidifier fix my humidity issues or should I move up to the 1870 model. Any assistance would be greatly appreciated. Thx
I suppose an additional problem is that if you cut a new hole in a post tensioned slab that (after carefully locating where you can cut) that it should be a circular (drilled) hole in order to avoid compromising the structure of the slab and creating a point where the concrete can give (as with a square or rectangular cut.) It seems as though a lot of things change where after-the-fact alterations are being made once pre-stressed concrete is introduced into the mix.
thx Matt. Very educational. Would like to know more about the decision making process (post tension vs. rebar). If you are building on expansive soils, would your preference then be post-tension? You mentioned that your preference is rebar, but tell me when is the right time to choose post-tension. thanks
Off topic you don't have any videos on propress copper plumbing if you're looking for ideas for videos I would love to know what you think about propress vs sweting copper pipe/fitting
Do you have any input on pre-installing in ground piers on a new slab? I'm looking to build a home to turn around and sell and I'm in Denton County in Texas. Thanks in advance
That slab has already been tensioned. The wedges are in. I’ve seen post tensioned slabs move enough to make high or low areas. But that was a structural floor.
@@MrNorthstar50 Think about what you just said. If each tendon is PRE-tensioned, to say 50 tons, what did they anchor each and every tendon end to to resist that tension? Pre-tensioning/ pre-stressed concrete is only doable in a factory setting, and involves 1-way tension for resisting loading along a single axis (such as concrete floor planks, single or double Tee's), and a substantial structural frame to jack against while the concrete cures.
Mr. Bruce Ryan is correct. The cables have already been tensioned. The tension crew sprays the cables with paint at the slab just before stressing them. The white paint is visible on several of the cables. Then they stress the cables and call the engineer. The engineer comes out and measures the each cable's elongation with the help of the spray painted marks. Assuming the elongation distance is correct; and that no wedges have given out, the engineer signs off on the cables being cut and the holes grouted.
Hey Matt, love your videos. Can you please add some content/advice on foundations on sloping sections? I am about to start building on a sloping gradient section. Any advice would be awesome.
You engage the services of a competent structural engineer in your locale, who knows the conditions, the local practices, and knows the geotechnical engineer he needs to advise him on the soil conditions (after drilling/ testing) that he will have to design with. You have succumbed to the "Matt is GOD" mentality. One, he won't answer a question such as you pose, and if he did, it means he is a fool with no regard for his or your liability or ultimate success. There is no "Universal Answer" unless you are willing to accept "It Depends". Slope is only one variable in the equation, perhaps not the most critical one.
What do you know about Helix Micro-rebar for slab foundations? How does it stack up to slab with rebar? BTW, thanks for these videos. As a future "new construction" homeowner, I've learned SO MUCH from them.
It's very important that PT slabs are tensioned at 3 days, not before and not after. If you do plan on tensioning at 5 days, let your PT supplier know way up front.
If you see this message please comment Matt. I'm in contract on a new build home with Richmond Builders in NorCal. On our half bath, I noticed there is no drainage pipe for the toilet, one can only assume no pipe was installed. Could they fix this problem on a concrete tension slab?
Does anyone use pre-stressed slabs - like they use on bridges? Isn't that supposed to need less concrete? Wouldn't that allow you to cut through for plumbing etc?
If post-tensioned slabs work in the south with several inches of movement, why not use it in the north where there is movement? I understand most houses have full basements, but a great use example would be a garage. Rarely are frost walls poured for a garage slab to prevent heaving in the north. Why do I never see these used up here?
I am trying to reconcile vids on "Future-Proofing" a house by putting a PVC pipe out the eaves, and then hearing about the horrors of alterations to a post-tensioned slab. And then hearing, almost as an afterthought, about pier and beam foundations. I am also wondering about the whole rock at and below 6" (so use slab on grade) in relation to having to drill piers (because of depth of expansives). I don't see how those two conditions can exist simultaneously. Here in Colorado, frost and extreme expansive soils are serious issues. I know of no builder or developer who does any slab on grade residential construction. In fact, those who do basement/ walkout slabs on grade have in several cases, been put out of business due to differential heaving, and the resultant class action lawsuits. Even the cheap bums have been forced to go to structural slabs, or structural wood-framed floors over crawls, just to preserve their own business operations. If I were building in Austin, I would absolutely push beam and pier. First, I really dislike hard floor surfaces, and the unyielding concrete slab is a lot less forgiving on the occupants (walking on) than any wood-framed floor assembly. Second, the ability to alter and renovate without extreme hassle and potential for injury would be a huge issue for me. Another issue is that of thermal mass. We find that low thermal mass radiant floor systems (such as Warmboard) are significantly more controllable, and thus significantly more comfortable, than high-mass systems (thick concrete slabs, or even gypcrete). The detailing I have seen on this channel, as regards the slab/ wall/ exterior ground plane interface seems pretty deficient to me, with a continuous band of thermal bridging (unless one does the fairly easy step of extending continuous exterior insulation below the ground plane). The knowledge of how to do exterior insulation for unvented, conditioned crawl spaces is well documented, and not particularly difficult. I find the advantages, at least in Colorado, are so great that I won't even spend any time doing cost comparisons. And it might be useful to explain that the post tensioning works by putting the entire slab in extreme compression. Any bending forces applied to the slab (such as by differential soil expansion across the length of the slab) will induce a tension force in some part of the slab cross section. However, the concrete of the slab will not be subject to tension, per se, until that applied or induced tensile force EXCEEDS the static (pre-loaded) compressive force in the concrete. Designed properly, the concrete in the slab never experiences a NET tension.
Pier and beam in Texas is double the cost of a slab. You are not going to see tract developers use anything but a post tensioned slab. I also like the idea of a pier and beam for the reasons you mentioned
@@jl9678 Texas is far from the only locale where usual and customary practice is far more important than what would be objectively considered to be the best in terms of long-term value. Here in Colorado, the national home builders account for an overwhelming percentage of the new home construction (I'd guess at least 98%). Bottom line is everything, knowing they can and do evade responsibility for failures during the warranty period, and get away with profit intact. The worst part is that it sets the level of expectation with the clients/home buyers as regards first cost/ price points. And, it really shapes the labor force, and trade practices, and not for the good, in my estimation. It is a very discouraging landscape for those of us that embrace seriously good construction practices, because we have to fight the perception that we are "rip-offs". Matt has taken a similar stance to myself; do an excellent job, get known for that, hold your ground with clients, and don't expect it to be easy.
Matt I had an old guy framing a house for me years ago. The owner came by and kept on and on about several surface cracks in the slab. My framer got tired of listening to him, walked over and said "You tell me how to pour a slab without it cracking and you and I will never have to work another day in our life. He never said another thing about the cracks.
Ha! So true.
It is possible to avoid cracks but its hard to do. I did a mat slab 75cm, all rebar and self-consolidating and ponded for over a month and it never cracked - but maybe that was just lucky !
@@Kpopzoom by "ponded" do you mean kept moist? I've read that one of the primary reasons concrete cracks is shrinkage caused by drying too fast; and that keeping the slab covered with plastic allows it to cure much slower and avoids some cracking. It makes sense to me, but I have no practical experience.
@@scottcraig1047 By Ponded I mean a small dam is built all round the slab (in this case using the waterproof turned up) and the entire slab is filled with water to a depth of a few inches. The water is then kept topped up daily to maintain the slab effectively underwater for the entire curing period.
surface cracks mean nothing because you have rebar, but most homeowners aren't structural engineers or contractors and don't understand this, of course!
I would love to see the slab actually being tensioned
I hear you, however is technically being compressed 😉
It’s pretty dull. There is just a calf sized electric tool that pulls on the cable. There are stories of a cable breaking and coming up through the concrete and whipping around. Sort of a rare event. Never saw that happen. Btw that slab has already been tensioned. The wedges are in
My 1970’s post tension slab saved our house! We live on a steep slope and our house started sinking. It was 5” out of level and not a crack in sight! It moved as a boat, as Matt described. A rebar slab would likely have broken. The remodel part is also an issue. We paid over $600 for someone to essentially bring in a giant fish finder X-ray contraption to map our cables ... and then you can only cut around them. I’ve been told they’re used a LOT in parking terraces and other commercial applications. Not sure how they impact load?
Also: I was REALLY glad to hear Matt say he avoids running water supply lines under or through slabs!!!! In Southern California, this has caused SERIOUS ISSUES with plumbing leaks, particularly with copper pipes! I would NEVER run my supply lines under cement!!! If you haven’t had a slab leak here yet, be prepared because sadly, you will! It’s just a matter of when! Good episode!
Bruce Ryan Yes, rare. Yes, the cables whip up. Never stand on the slab your stressing. But the real danger is the concrete it throws.
Really he can't because he's actually just kind of borderline trespassing
In Phoenix, pretty much all new homes are post tension. House I just had built is a post tension, I prefer rebar slab because you can remodel and move plumbing around in the future. Post Tension, you are pretty much locked. The cables were not tensioned for about 6 months. The builder waited for the full framing to go up and they did it just before the stucco install. And not a single crack, even small shrinkage cracks, the slab turned out perfect.
Why can't post tensioned beams be untensionsed for remodeling?
big O because they cut off the tail after placing it under tension. If you released the tension - the cable would pull back into the slab never to be seen again.
Why wait so long?
Incredibly clear, concise and thorough explanation of the process. Thank you Matt for sharing your knowledge.
I bought a house that had a post tension cable failure where 2 cables crossed near a perimeter wall. The failure probably occurred many years before I bought the house and it was difficult to diagnose the cause of the failure. My guess is that water got into the end of the cable because the recessed hole for the cable slips was not filled and sealed properly and corrosion occurred. When one cable broke the release of energy caused the other cable to break. There was a 12 inch crater in the slab. I watched the guys that did the repair and re- tensioning and it was fascinating how they were able to fish out the old cable and splice everything together.
just admit your house would have been better off with a traditional foundation.
I’ve seen builders treat the tension technology has some kind of magic that will overcome the basic laws of engineering and physics.
If the slab is poured onto unprepared ground and you exert enough pressure/the weight of the house on one side, it’ll crack into several large pieces. One house I saw cracked and had sunk 4 inches on the backside of the slab, the house wasn’t even a year old.
We dug down and found the builder had put the slab in contact with fill sand on the perimeter wall.
He thought his magic tension system would allow him to forgo basic concrete work.
I always like your videos. I am retired now but spent my entire working life in the building industry engaged in the professional (architectural) side of things. In my country (Australia) we almost never do post tensioning on domestic ground slabs but it is used a lot on commercial projects where its main advantage is increased spans and hence wider spacing between columns.
I really appreciate your videos and your commitment to building science. Some of what you do would be regarded as 'overkill' here but our climate is probably a little kinder than what you have.
Love it. If you pretension the slab a day or so after the pour then the final post tension, it will help prevent those minor cracks! 👍
Great call! What are you mainly using on your slabs?
Matt Risinger we have had really good success with the post tension on our engineered slabs which we use a lot on our Barndominium builds. But we also use rebar on occasion. The one we poured this week we used rebar with 12” spacing.
I’m hopeful that my point was made in this video that Post-Tension is a great foundation but my preferred slab is rebar.
Matt Risinger yes sir. That point was accurately made. Always love your content! 👍🤠
PT is very popular in the southwest, almost all slabs are PT. In my industry (ironworker) we do the post tension on the big commercial and bridge projects. PT is no joke I have witnessed the damage it can cause.
Had my day's first _"learn something everyday"_ moment! Ahhhh. Refreshed! 🍺🍻
glad you mentioned remodel. Thats a major BFD someday on a prj
I believe that slab has been tensioned already. Look at the white spray paint lines on the cables . Those are the reference marks sprayed prior to stressing by the stressing crew immediately before they stress. The stressing crew, sprays the cable, stresses it; and then leaves the cables un-cut. Then, an inspector or engineer will come out and measure the cable elongation. The elongation (strain) is used to calculate the amount of stress the cable is under; and to make sure it is within design parameters. Once the inspector signs off on the proper cable stress; the stressing crew returns to the site to cut all the cables and grout the holes.
ruclips.net/video/3UKh8vTpnrY/видео.html
You should of made this video, this guy lacks your expertise. But hey he tried.
Bingo
Matt, the reason for the cracks in the slab is not the downward motion of the edges as you had described. You mentioned the reason in the name itself. It is shrinkage. Each and every little bit of concrete shrinks in all 3 dimensions. What causes the cracks is the addition of each bit of concrete to how much movement a given direction will experience. The length of this slab is longer than its width, as you said a rectangle, so the addition of all that length will add up to enough shrinkage movement/tension that a crack will occur perpendicular to that length. This is the reason sidewalks are scored with control joints in the short direction... as the long long direction is the one where tension will build up.
Matt, the use of PT systems for slab on grade is really surprising to me, and i'm not completely sure how it is supposed to be achieving any form of crack control to be honest. Typically the reason we use PT slabs is to control deflection (and as a result SOME of the cracking), so we end up basically inducing a "camber", thus the slab flattens once the dead and live loads make their way onto it, instead of deflecting, so the cracks that are prevented as a result of this, are typically the ones that you would notice on the underside of that slab, not the top. Let me say that i am not an engineer, but an architect, and certainly cannot claim to be an expert on this subject. Thanks for the video.
I cut one of those tension cables once, it’s loud when it separates. Turns the slab into a guitar.
Not quite. Repairing pt cables is pretty straight forward. Open up the cable ends enough to grab hold of the cable ends. Where the cable has been cut, splicers, similiar to chinese money. Allows for the cable restretch.
Thank you so much for this video. We are building a brand new home and noticed hairline cracks like the ones in this video. But they are not higher than each other so don't believe they are structural foundation cracks. Thanks to your video, I can breath a sight of relief.
I am building a new home in AZ, and I have cracks in my Post-Tension slab. Your video has eased my mind that it's going to be OK.. Thank you so much for this video..
Its worth mentioning from a life safety side. I have been designing, installing and stressing thousands of slabs and a tradesman coming later that cuts a stressed tendon with 32kips of stored energy can kill. I have witnessed it in high rise decks. Only 3 days after stressing.
@@marcmyers1465 Its not very much. All the tendon stressed forces are "inside" the slab. Approximately 8-10" from face of concrete. Also, the concrete cover on the top of the tendons is more than adequate for tendon containment. Even at recessed patio areas. I would assume all the tendons are in a flat plane with very little drape. No the instance of reverse curvature blow out is very small. Interesting is the (3) tendons in a bunch. Even if this is for a bearing wall of surface mounted column I wouldn't place them that tightly grouped. It would be better to place them in flat plane 6" CC spacing. Lastly, then Ill shut up. The finish sealing on the tendon ends after cutting is very important ti use rust proofing sealer/paint and encapsulate the tendon ends with non-shrink, non-metallic grout.
Thanks
Thanks, Matt, as always very informative. I've never been involved with building a post-tension slab so its really cool to get acquainted w/the process. I agree, pier & beam foundations have advantages and cost-saving potential, especially on steep terrain.
Was interesting to watch this. In the 70's I was walking through a house that was under construction. This house had already been framed and sold. The slab was on grade with post-tensioning. When I walked into the master bath, I noticed a scary thing. They had used a jackhammer to remove the slab where the bathtub was going to be placed. Right through the center of the hole running the long direction was a tensioning cable. I had to laugh and went to get my dad. He could not believe that they were even considering the remote possibility of cutting the cable to put in a sunken bathtub. Presently I live in a house with post-tensioning for the slab reinforcement. Sadly, after watching the builder construct homes near me, they did not wait for anything with the slab. The tensioning was done within 72 hours of the slab being poured. The framing was going up and the slabs were still green in color. The other builders in the area waited 28 or more days before framing the new homes.
Post tensioned slabs have been used on almost every home built in Arizona for the last 20 years. It has been used in commercial buildings for decades. Just sold a home 16 years old with zero cracks, including the garage. It is a fantastic way of building a slab on expansive soil which we have a lot of in Arizona.
he said those are braided cables, hes wrong, those are twisted cables with a twist every half inch, up to a twist every two inches. no one uses braided cables for construction, under tension they deform at the wire crossings. the most popular cable is two or three opposing twisted wire layers, (wire rope), an example, first layer clockwise, next layer counter clockwise, top layer clockwise. makes a strong cable that will puller uniformly without internal stress.
Most residential new construction slabs around the Phoenix metro since 2000 are post-tension slabs. We have clay soils here that swell and shrink with water absorption and loss. Post-tension slabs combat the moving soil. Great video!
Should have started tension as it was curing; and finished it after it cured... that would have prevented cracking on the slab. Thats what they do on commercial projects where a tensioner is onsite.
that's called pretensioning
That’s pretensioned concrete. This is post tensioned concrete once it reaches 3000 psi (typically)
@@itech301 Only if done before the concrete is poured. xephael is suggesting a two-stage post tensioning. Sounds to me like the equivalent of pulling the forms on multi-story cast in place after a week, then immediately placing shore poles and beams to prevent deflection or cracking for the balance of the 30 days to "full" strength. The pole shores leave a lot of space for construction activities to proceed on that floor level, whereas the forming systems left in place mean one can't do anything on that floor until they are stripped.
Agree. Initial tension and final tension is better, typically at 3 days then again at 7-10 days after pouring.
But to be fair that is probably quite costly for your standard house slab.
I suspect that slab has already been tensioned- frame at 2:38 shows swedge anchors in the pocket and white paint in the tail of the cable, which is typically done to measure stretch (strain) of the cable as tensioning. They just haven’t cut the tails off yet, or possibly left them to retension
Mat. I’m sure I’ll get no response out of this. But???
You pretty much explained how you fix a stretched pressure cable. You said that they are greased up pretty good so it’s easier to stretch them to ad the strength to the slab itself. On the opposite end of what you were showing is a snatch block. When you put the tensioner on then you were showing. But first cut that snatch block off. Then they actually make a sleeve that goes over the top of the cables. You weld this sleeve to both cables and start pulling. You can pull the old cable out while you are pulling the new cable in. If you have a cut or broken cable let’s say where the apprentice hit it with a jack hammer. You must clean the cable where it was broken and splice it back together so the complete cable can be removed and the new cable can be drawn it. Once it is in. You cut it at the far end. Put a new tension plate on the end. Draw it back down tight.
Now that’s a long Paragraph
I appreciate your explanation of the pros and cons of all construction choices.
Wow. I didn't know about the danger of jackhammering the cement around those cables. I have a post tension slab and I had a collapsed drain line in my washroom. I did a remodel and moved the sewer and water lines. I hit those cables and ripped the plastic of of them. they didn't break and it is covered back up now with 4500 PSI cement and then tile. Thanks for the info.
If you would of chipped and broke that cable, trust me you would of had chocolate pudding in your underpants. That's if all went well for you.
I'd be pretty keen to see you review basalt fibre rebar in a slab as an alternative to steel.
Best explanation by far. Thanks Matt!
Very interested seeing how you build stateside compared to how we build here in the UK !
We have PT system in the UK as well mate
Probably could have made a 2 minute video of this if you just said it was cheaper in the beginning.
The cheaper it is the more it will be defended or pitched as better by contractors looking to maximize profit.
Would be curious to see how much cheaper the labor end of it is too, including the rental (if needed) of the machine that does the tensioning.
Very very informative. Thanks for sharing. Channels like yours are absolute gold
Hey matt I love watching your videos they are very educational. I live up in mass. And like learning how different things are in the south. Also love learning things cuz people can take anything from you but not your knowledge...keep up the videos...by the way do you sell those build hats? Would love to get one
Should be tensioned within 72 hours and kept most that will reduce the shrinkage cracks.
I do special inspection on this type of construction as well as many other types of concrete construction.
Best feeling taking first steps on cured concrete. 👍 video
I'd like to see a video on Helix concrete slabs as a foundation.
Interesting. I'm a concrete pump operator from NW FL. I've never seen tension cables on a house slab. Most around here are done with rebar footers/grade beams, then use wire remesh sheets or rolls. Very rarely do I see rebar mat slabs either. It's sometimes used on wetlands or on the sandy beach. Stem wall foundations are most common around here.
The tendons have been painted and the paint is 6 or so inches away from the concrete. They've already been tensioned. Typically we tension the morning of the second day after placing concrete. If you wait 7 to day days the concrete cures too much. Engineers typically require it be tensioned within 72 hours.
Home Inspector here. I know of a very unhappy construction site manager who is upset because he was called out by someone ...... 6weeks after pouring the slab, it has still not been tensioned. There is now a crack down the center varying in width. They have a staff-paid Structural Engineer coming out to verify everything is 'ok'.
I was doing a commercial job and I was in the dining area when I heard the cable get cut. Very recognizable sound and I was standing right on top of it. The guys outside trimming off part of the foundation cut right through it with the gas saw...
Would love to see a guided tour of a concrete slab or other job that uses twisted micro rebar (helix) as its primary reinforcement! It would look to be right up your ally.
In south Louisiana we don’t have the expansive clays instead we have nothing but river silt to build on so there is nothing solid to build on. Consequently, I advocate for post tension.
Matt, I have a question about the BuildApp webpage. Seems like all the videos I've watched have an issue with the audio syncing can you correct that problem?
i just noticede the candian lumber in the background. OH CANADA!
Our home and native land ! (?)
We need that in North TX. Foundation repair is a constant.
I was in a 20 story hi rise and one on the guys on a crew hit the tension wore on the core tower on a almost finish building. It was so loud and freaked everybody out as the building shook and it took almost a year to fix it.. UUUG is was so bad. Always ask before you drill!!
😳 wow
Always scan and talk to the Post Tension inspector or contractor or both before drilling
I just made a comment on these types of slabs should come with a map with exact measurements to stop or at least reduce the chance of hitting/cutting one.
Cables break often. Most times you don’t know unless you feel it with the rotohammer. Been there done that.
august they do. Check out the PT shop drawings. You’ll get extremely close with them so long as they didn’t need to adjust or move anything in the field.
I would like to see about the different ways to build a basement on a new construction house and then how if possible to build a basement in a pre-existing concrete slab house
Other than cost, what would be the disadvantages (and advantages) of doing both rebar and post tension in combination? Is there ever a time you would do both together?
Rebar and tensioned tendons are always done together.You cant tension concrete without having rebar .
Wonder if/when glass fiber reinforced or basalt fiber reinforced rebar will come down in price to become cheaper than steel rebar? I think Owens Corning's "pink bar" or Aslan 100 fiberglass rebar may now cost about the same as steel.
Helpful. Only worked with rebar slabs so this was good to see. I would love to see a tensioned slab being cut or demo-ed. Could be a good lesson.
At 3:18 of the video, the tendon has been tensioned and the two half- circle wedges have been "seated." They are waiting to be cut after city inspector signs off.
Had to have two cables replaced on my slab since the foundation lifting company snapped a few jack hammering through my garage floor. They had to pay for the repair since I told them about the cables and said they would scan to avoid them but the crew did not even when I reminded them.
The soils where I live are mostly very stable, so 4" thick concrete is typical for slab on grade, and no reinforcing is put in except in the toe at the perimeter.
We did do one job, however, that was in an area of town that has expansive clay. That one got a 12" thick slab with 2 layers of #6 bars at 24" O.C. both ways. It did not get a perimeter toe, the slab itself was considered by the engineer to be strong enough to resist any uneven shifting. That seems a bit over optimistic to me, especially considering the enormous size of that place, but the engineer put his stamp on it, so he owns it.
I miss doing Construction It Was A Talent Of Mental Science I Was Blessed To Work On 100 Million Dollar Projects To A 200.00 Sheetrock job Learning Everything Is A Blessing Being Mechanically Incline Is The Greatest Gift Because When Everything Falls We Build It Back Or Something New 👷♂️👊🏽💯
Hey Matt you mentioned that you don't like to bring water supply lines in thru the slab - can you show some details about how you bring them into the home?
My current house is post tention. Still have the hairline cracks and it was done 38 years ago. I'm afraid to tear up hallway flooring because I know there's an issue. Just have no clue how severe it is. Right side is off by 3/8 inch but the left is off by 1 inch. Walls on the 3/8 side have some splitting where tape and float was done on corners of 1 wall and under 1 window. Have to do some grading on the left side as last owner was an idiot and built up the ground by 2 inches so water flows toward house. Also installing rain gutters to direct water away from effected areas.
Now I am going to RUclips post tensioning cable being cut. Just because of the description you mentioned in the video...... 😳
In the uk we use black and bean foundation that means there’s an empty void under the house until you get to your highest point of the hill. From there you build a regular house from the flat surface from the blocks (concrete slabs) and beams (concrete beams just like steel beams in warehouses). The void foundation has some special bricks spread throughout to help let gasses out. This is my favourite building style
Grant it’s actually block and beam. Gasses? Hope your not in the building game.
Grant Cook auto correct had me there. I was for a while.
Grant Cook I know it’s block and beam
I too would love to see the slab actually being tensioned
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@Matt Risinger what about using alternative materials for reinforcing the concrete, fibers polymers materials in alternative from steel?
The question being durability and corrosion. Maybe a video on that
Thank you Matt for this information. We're in far Northern Wisconsin we wouldn't use a system like this.
Very wise on your end, take advise from someone who clearly said he has minimal experience on post tension.
Thanks!…you always have something great, so we can learn!…
Does anyone pre tension slabs? I’ve heard for like parking garages that they tension the cables before it’s cured then release the tension afterwards.
A coworker built a home with this system but the concrete was stamped then stained. Sounded like a substantial cost savings, compared to the NE where a slab home would be a tough sale. Most everyone expects below grade living space.
Post tension is good stuff. A monolithic pour with extremely strong results. Rebar comes with its own set of long term problems. 6 of 1 as they say.
When remodeling and cutting a post tensioned slab, we locate the cables and mark them so we know where to cut the slab. Update your video to include this information.
lol you think this idiots videos contain any factual information what so ever?
Best information I learned a lot from this !
Hi guys, notice:
* plastic on foundation under steel.
* when site security fences not required all steel ends capped.
* barriers for sub terrarium termites, especially collars around plumbing.
* new testing on permeability of water in concrete to reduce spalling.🔎💡
How do you put the wall on the anchor bolt? Do you have to put bottom plate first and then put the rest of the wall on? Or you build the wall on the ground and then lift the wall into the anchor bolt?
Good vid once again. On a side observation, I bet Matt is regretting black as the official "Build" color as we get into these summer months. The difference in a light color vs dark is tremendous when you're out in the sun.
I love to know how this has held up.
Many tract builders in expansive soil areas will use post tension to minimize liability for slab shifting and structural damage. I’ve seen a number of garage floors with warnings about sawcutting and the danger caused by snapping a tensioned cable. YIKES!
Matt, I have a typical track home in southern California and I am going to update the floors on the second story. How would you remedy the sound transmission? I am thinking some thick Advantec with screws and some form of adhesive.
it's not track it is tract.
Hello Matt. I'm curious in what your job description is. And if possible how you got there. I have my own construction business and I would love to expand, mainly because I would prefer to do the planning rather than the execution. I'm just getting worn down, cuz I'm my own employee, and on top of that I run alot as well. I'm just wondering if I can stay in construction yet "move up" to possibly earn more money and help build or repair more homes.
Thank you, have a great day.
Interesting video. Why is that foundation so darn high? It's about 3 feet higher than the existing houses in the neighborhood, and the house is going to stick out like a sore thumb. I'm a little confused how pulling the rods will cause them to push more tightly against the concrete. Are you sure they don't twist them more to tighten them? Someone told me once that the slab on my house is post tension but I'm kind of skeptical.
Hi Matt! So I have a quick question in regards to post-tension foundations - Our new home in your area has a post-tension foundation as well as soil injections to the whole lot. What do you think of soil injections? Do you think they help? Thanks!
How thick are your slabs. I don’t think they do either one of them in JacksonvilleFl.
Matt I live in Killeen Texas. My home is a single story 3600sf with a spray foam attic. I have two 3.5 ton air conditioners. Will an 1850 Aprilaire dehumidifier fix my humidity issues or should I move up to the 1870 model. Any assistance would be greatly appreciated. Thx
Is it possible to do a combo of tension cables and rebar (although maybe not quite as much rebar) and the metal mesh?
I suppose an additional problem is that if you cut a new hole in a post tensioned slab that (after carefully locating where you can cut) that it should be a circular (drilled) hole in order to avoid compromising the structure of the slab and creating a point where the concrete can give (as with a square or rectangular cut.) It seems as though a lot of things change where after-the-fact alterations are being made once pre-stressed concrete is introduced into the mix.
thx Matt. Very educational. Would like to know more about the decision making process (post tension vs. rebar). If you are building on expansive soils, would your preference then be post-tension? You mentioned that your preference is rebar, but tell me when is the right time to choose post-tension. thanks
Great video. Happy 4th of July Sir!
Rebar slab on grade with insulation pad are the best in California never seen tension slabs
Off topic you don't have any videos on propress copper plumbing if you're looking for ideas for videos I would love to know what you think about propress vs sweting copper pipe/fitting
Do you have any input on pre-installing in ground piers on a new slab? I'm looking to build a home to turn around and sell and I'm in Denton County in Texas. Thanks in advance
Concrete can also be pre-tensioned in which the steet tenons are tensioned before the concrete is poured and are exposed directly to the concrete.
That slab has already been tensioned. The wedges are in. I’ve seen post tensioned slabs move enough to make high or low areas. But that was a structural floor.
I think it's probably pre-tensioned because they usually cut the cables after after the final tension is applied.
@@MrNorthstar50 Think about what you just said. If each tendon is PRE-tensioned, to say 50 tons, what did they anchor each and every tendon end to to resist that tension? Pre-tensioning/ pre-stressed concrete is only doable in a factory setting, and involves 1-way tension for resisting loading along a single axis (such as concrete floor planks, single or double Tee's), and a substantial structural frame to jack against while the concrete cures.
Mr. Bruce Ryan is correct. The cables have already been tensioned. The tension crew sprays the cables with paint at the slab just before stressing them. The white paint is visible on several of the cables. Then they stress the cables and call the engineer. The engineer comes out and measures the each cable's elongation with the help of the spray painted marks. Assuming the elongation distance is correct; and that no wedges have given out, the engineer signs off on the cables being cut and the holes grouted.
I agree, I believe a partial stress have been performed at the least. Then a full stress about a week later.
Not out here in southern California.
Hey Matt, love your videos. Can you please add some content/advice on foundations on sloping sections? I am about to start building on a sloping gradient section. Any advice would be awesome.
You engage the services of a competent structural engineer in your locale, who knows the conditions, the local practices, and knows the geotechnical engineer he needs to advise him on the soil conditions (after drilling/ testing) that he will have to design with. You have succumbed to the "Matt is GOD" mentality. One, he won't answer a question such as you pose, and if he did, it means he is a fool with no regard for his or your liability or ultimate success. There is no "Universal Answer" unless you are willing to accept "It Depends". Slope is only one variable in the equation, perhaps not the most critical one.
Could you do a video on pwf/wood foundations.300,000 in usa.thinking of,in Michigan.thanks.
What do you know about Helix Micro-rebar for slab foundations? How does it stack up to slab with rebar? BTW, thanks for these videos. As a future "new construction" homeowner, I've learned SO MUCH from them.
Can ICF or other monolithic concrete systems solve the shifting ground problems?
How does one know if the house they're working on has a rebar slab or a post-tension slab
It's very important that PT slabs are tensioned at 3 days, not before and not after. If you do plan on tensioning at 5 days, let your PT supplier know way up front.
Matt, what happens to a post tension slab if a fire burns the structure to the ground?
I’d like to see a garage over a basement and your perspective on the engineering.
Have you ever looked into micro rebar? How does it compare?
If you see this message please comment Matt. I'm in contract on a new build home with Richmond Builders in NorCal. On our half bath, I noticed there is no drainage pipe for the toilet, one can only assume no pipe was installed. Could they fix this problem on a concrete tension slab?
Cost of steel is crazy now..we added to stock a few years ago but not near enough
Post tension is pretty much standard for track homes in Las Vegas.
Does anyone use pre-stressed slabs - like they use on bridges? Isn't that supposed to need less concrete? Wouldn't that allow you to cut through for plumbing etc?
If post-tensioned slabs work in the south with several inches of movement, why not use it in the north where there is movement? I understand most houses have full basements, but a great use example would be a garage. Rarely are frost walls poured for a garage slab to prevent heaving in the north. Why do I never see these used up here?
I am trying to reconcile vids on "Future-Proofing" a house by putting a PVC pipe out the eaves, and then hearing about the horrors of alterations to a post-tensioned slab. And then hearing, almost as an afterthought, about pier and beam foundations. I am also wondering about the whole rock at and below 6" (so use slab on grade) in relation to having to drill piers (because of depth of expansives). I don't see how those two conditions can exist simultaneously. Here in Colorado, frost and extreme expansive soils are serious issues. I know of no builder or developer who does any slab on grade residential construction. In fact, those who do basement/ walkout slabs on grade have in several cases, been put out of business due to differential heaving, and the resultant class action lawsuits. Even the cheap bums have been forced to go to structural slabs, or structural wood-framed floors over crawls, just to preserve their own business operations.
If I were building in Austin, I would absolutely push beam and pier. First, I really dislike hard floor surfaces, and the unyielding concrete slab is a lot less forgiving on the occupants (walking on) than any wood-framed floor assembly. Second, the ability to alter and renovate without extreme hassle and potential for injury would be a huge issue for me. Another issue is that of thermal mass. We find that low thermal mass radiant floor systems (such as Warmboard) are significantly more controllable, and thus significantly more comfortable, than high-mass systems (thick concrete slabs, or even gypcrete). The detailing I have seen on this channel, as regards the slab/ wall/ exterior ground plane interface seems pretty deficient to me, with a continuous band of thermal bridging (unless one does the fairly easy step of extending continuous exterior insulation below the ground plane). The knowledge of how to do exterior insulation for unvented, conditioned crawl spaces is well documented, and not particularly difficult. I find the advantages, at least in Colorado, are so great that I won't even spend any time doing cost comparisons.
And it might be useful to explain that the post tensioning works by putting the entire slab in extreme compression. Any bending forces applied to the slab (such as by differential soil expansion across the length of the slab) will induce a tension force in some part of the slab cross section. However, the concrete of the slab will not be subject to tension, per se, until that applied or induced tensile force EXCEEDS the static (pre-loaded) compressive force in the concrete. Designed properly, the concrete in the slab never experiences a NET tension.
Pier and beam in Texas is double the cost of a slab. You are not going to see tract developers use anything but a post tensioned slab.
I also like the idea of a pier and beam for the reasons you mentioned
@@jl9678 Texas is far from the only locale where usual and customary practice is far more important than what would be objectively considered to be the best in terms of long-term value. Here in Colorado, the national home builders account for an overwhelming percentage of the new home construction (I'd guess at least 98%). Bottom line is everything, knowing they can and do evade responsibility for failures during the warranty period, and get away with profit intact. The worst part is that it sets the level of expectation with the clients/home buyers as regards first cost/ price points. And, it really shapes the labor force, and trade practices, and not for the good, in my estimation. It is a very discouraging landscape for those of us that embrace seriously good construction practices, because we have to fight the perception that we are "rip-offs". Matt has taken a similar stance to myself; do an excellent job, get known for that, hold your ground with clients, and don't expect it to be easy.