Concrete Countertops: How reinforcing works
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- Опубликовано: 16 окт 2024
- Learn from Jeffrey Girard, President of The Concrete Countertop Institute, the principles behind how properly reinforced concrete countertops can enable you to have confidence and avoid problems. Jeff explains how concrete countertops behave like beams, not slabs on grade, where to place the reinforcing and why (including cantilevers) and what materials are most reliable for reinforcing precast concrete countertops. He also touches on how GFRC reinforcing works, as well as gives amazing examples of what a properly reinforced precast concrete countertop can do. View this video if you are a concrete countertop professional who wants to make high performance concrete countertops.
For more about how reinforcing works in concrete countertops, see these helpful articles:
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This is a phenomenal video. I'm a contractor but have had no experience with concrete countertops up until now. I'm remodeling my own kitchen, and have decided it would be a good time to use myself as a guinea pig for my first attempt at making concrete countertops. Thank you!
Wow. Your ability to explain this in discharge logical and straightforward terms was amazing. If only every educational video on RUclips was this clear. I would be a genius.
I'm glad you liked the video Matt!
Excellent explanation for those with little to no experience designing concrete structures. You kept it simple and very understandable.
People like you is why RUclips is great! Thank you.
Perfect explanation
Fantastic video! This was a really well thought out and presented explanation of reinforced concrete design. I have taken many concrete design courses and this is by far the quickest and most intuitive approach I have seen detailing tensile and compressive strength function and placement of reinforcing. Everyone needs to watch a good 10 mins of something like this, not just for concrete, but for the nature of materials and stresses for building. Thanks!
Great video, very useful information. Thanks Jeffery!
You are very welcome!
I am so glad I watched this before beginning my countertop build. THANKS!
Be sure to read this too! concretecountertopinstitute.com/free-guide-diy-concrete-countertops/
old video...still VERY relevant information and well communicated as well. Great job.
Thanks Derek!
Thank U Professor....Really enjoyed this session...Thx. again from an old ME.
You are very welcome Jerome. Thank you for the kind words!
Very well explained. I am going to be building these in my house and needed to address these issues. Thanks for posting this.
Really wonderful video. Easy to understand and apply. Great pictures to go along with your wording. So happy I found this.
Wonderful. Clear and to the point.
Easy to understand teaching that applies to a wide range of applications.
Keep it up.
+kbaxter777 Thanks for the compliment! Please note that there are several other free training presentations available at www.concretecountertopinstitute.com/class-schedule/#Webinars.
The tensile modulus of steel matches concrete while glass does not….please elaborate on this point. It seems to me that cracks will form sooner as the glass is not properly supportive within the modules of concrete .
I assume that you are talking about the AR glass fibers used to reinforce GFRC. GFRC has a radically different mix design than ordinary concrete, and is more in tune with the flexibility of glass reinforcing. I have extensive articles and videos about GFRC here: concretecountertopinstitute.com/free-training-category/how-gfrc-works/
Tensile modulus is an indication of the stiffness of a material, in other words how stretchy or not something is. A high number means the material is stiff, and a low number means the material is stretchy.
Steel has a higher modulus than glass, i.e. it is more stiff and less stretchy. Therefore, with all else being equal, a strand of steel that's the same diameter as a strand of glass will stretch less than that strand of glass under the same load.
With conventional concrete (rocks, sand, cement, and water), the concrete's overall ability to stretch without cracking is extremely limited. Conventional concrete is brittle, which means that it doesn't take much flexing to cause a crack. The structural reinforcing material must take up all of the tensile forces and at the same time prevent the reinforcing from stretching so much under load that the surrounding concrete cracks. Because steel stretches much less than glass, it takes a relatively small amount of steel to resist the tension-induced stretching.
You can't use glass fibers and glass mesh (aka scrim) in conventional concrete because there's simply far too little that can be mixed into the concrete to provide the degree of tensile capacity AND stretch resistance that ordinary concrete requires to resist cracking.
Fiberglass rebar exists and can be used in conventional concrete, but the amount of fiberglass rebar that must be used to resist the amount of stretching that is necessary to prevent cracks in the concrete is much greater than the amount of steel that is required. So steel is the preferred method of structural reinforcing for conventional concrete.
I have always advocated using 9 gauge masonry wire for reinforcing. It's a true, structural reinforcing material, it has great properties, it is easy to work with and it can provide outstanding results when used correctly.
Great information 👍
Thanks Bro! This video was really informative. I appreciate that you took the time to do it!
You are very welcome!
Very educational video! It's one thing to say what to do, but this says why. Thanks for putting this together.
Excellent video on the explaination of forces to a countertop.
The backdrop was simply a piece of gray cloth, and I used two 4-foot shop fluorescent light fixtures with daylight bulbs on 6-foot stands. Pretty simple!
WOW! I learned so much from this video!! Loved the scientific explanations--now it all makes sense. Thanks so much for making this video!! Jody
Wow, well done; teaching not just what and how but why - Kudos! Excellent work, can't wait to check out your other videos, info, etc.
+Eric Smith Thanks! I'm glad you liked it. Be sure to check out all my free seminars here: www.concretecountertopinstitute.com/free-concrete-countertop-training/
Well this certainly explains why my first attempt was a failure. Ont to number 2!
Absolutely brilliant. Thank you for posting. This will help me with my concrete countertop for my outdoor kitchen.
You are very welcome Matt. Thank you for the kind words.
Wow, I just realized how little I actually knew by watching this video, very informative.
I'm sorry to hear about any cracking countertops! Exactly what I'm trying to prevent.
fantastic now i am feeling more confident about doing my own countertops
Very good video, Thanks. Like your pictures. I am making precast concrete stair treads for an outside deck. Your video has helped a lot.
great help! this vid answered many Q's i had about reinforcement. now i can embark on my 1st DIY project! thank you!
That's great Stephen! Keep in mind, I do also have the Level 1 Getting Started Self-Study program. Check that out here: www.concretecountertopinstitute.com/modules/info/self-study_training.html#GetStarted.
There is also a free 3-hour seminar here: concretecounter.infusionsoft.com/app/page/diy-concrete-countertops-free-training.
Very interesting, and sound engineering principles applicable anywhere and everywhere.
Brilliant and concise presentation! Thanks a lot.
+Herman Pick You are very welcome!
this informed my left ear very well!!!
Well done and thanks for taking the time to help us DIY'ers!
Jeffrey Girard what a great informative video mate, thank you!
You are very welcome!
Great video - you have a solid knowledge base of reinforced concrete.
Thanks for the great video Jeffery! Very helpful. I am making 1.5" thick pre-cast countertops for our kitchen and am planning on using 9 gauge masonry wire as reinforcement. Based on the info presented in your video, am I correct in saying that you would not suggest making a perimeter loop out of rebar or any other material? Also, what distance from the edge of the countertop would you recommend the reinforcement ending? I have heard that air trapping can occur if the reinforcement is placed too close to the edge.
I read your article on ghosting and in your words, "A third way ghosting occurs is when reinforcing already buried in fresh concrete is moved or vibrated". I was planning on using a vibrator to help the concrete settle in the mold..would you recommend not using a vibrator at all?
Please let me know what you think!
Caleb
finally a video that actually explains something. can i use thinset with fiberglass cloth? is it a necessity to have a thickness of 1.5 to 2 inch thickness?
Thanks for the great video. I am making a media center out of 1 1/4" black iron pipe and concrete. The two concrete shelves will span about 7 feet (x18" wide), and are supported on either end by the steel pipe skeleton. There may be up to 300 pounds of LPs on one of the shelves, dispersed evenly across the 7 feet. Can you recommend a slab thickness and rebar thickness? I was thinking of 2 1/4" slab, with 1/4" rebar running lengthwise every 6", leaving 1/4" from bottom of rebar to finished bottom
Whoa. I just learned a lot. Thanks for the great video!
You are very welcome!
The part about reo placement was well explained.
I wish my civil engineering professors explained it as well as this!
What a GREAT video!!! I'm a "why" person, so.. I don't like hearing "don't do this" or "do it this way", but... WHY to do, or not to do something. Thanks sooo much!! The last picture of the 500# on the plank.... VERY impressive! I'm SOLD! :D
VERY VERY HELPFUL VIDEO THNX A MILLION FOR THIS....GREAT JOB.....EXPECTING MORE VIDEOS......
Thank you!!!!! Excellent information!!
You are very welcome Sandra!
This is WISDOM. Thank you. Sharing is Caring. :-)
Thank you for the kind words, Carl.
I've been searching for information that would help me make a better product. Thank you so much for sharing your expertise with anyone who finds your channel. Thanks again!!
+Grace ValRioFarms You are very welcome!
What concrete is "good enough" foe a DIY countertop?, provided the reinforcement is done correctly and thank you for all the information given.
Antonio Fuentes Hello! I apologize for the extremely long delay in replying to your comment on the concrete countertop reinforcement video. RUclips was not sending notifications of video comments.
If you still have questions, please contact our office at info@concretecountertopinstitute.com for assistance in a timely manner. Thanks!
I liked the pictures you used, it was funny and explanitory.
Thanks Aiden. I'm glad you liked it.
How close may the reinforcing be to the surface of the concrete?And what type of concrete would you reccomend for the following project?I am building a 14'x21(w)x2"(t) 16" of the width to be canted. 3" bearing using #3 on 16"centers for support and #9 ladder wire tied for tensile strength A 2x6 wall provides the 3" of bearing The rebar will be L shaped with legs of 8 and 20 inches,the 8" leg will be inserted into a3/8 hole in the 2x6 studs and glued the 20 "will support the slab Thanks
Great info. Do you need to put in reinforcements if your cabinets already have a wooden tops which the counter will lay on. My cabinets have odd dimensions too (I have one of those weird, modern kitchens). Some cabinets are 12" X 40", 12"X14", 24"X30". Should I bother putting reinforcements in these or are they too small?
Great details for concret maker and they have to know this priciple
in conclusion, with concrete particularly, we have so much flexibility and it will tolerate lots of flex, especially when you try to realise your designs. however, there are some basic building block engineering tenets that this man puts back in your mind. concrete is seriously underexploited, but then so are most plant fibres too.
What is the best way to avoid the ghosting? You mention in your blog that pouring over reinforcement and placing reinforcement after pouring both can cause ghosting...as well as vibration...so what is your best recommendation on how to avoid this? Finally if it is pouring over the reinforcement, how do you suspend the ladder wire? Thanks Jeffrey!
Please see this article about ghosting: www.concretecountertopinstitute.com/blog/2012/10/how-to-avoid-ghostlymistakes-in-your-concrete-countertops/
My right ear is lonely. Give it some sound
You mention AR glass mesh. I have searched online for this and I've been unable to find it except in very large quantities from overseas. Is there a special store that usually carries alkali resistant glass or should I start snooping around my local concrete countertop shop?
Hello - would 1/4"-20 fully threaded zinc plated steel rod be too thick or unsuitable for a 1.5" thick concrete countertop? My sink cutout leaves the counter only about 3" to 4" wide infront and behind the sink. My first attempt cracked but had no reinforcement! Thanks for explaining tensile strength.
That size is fine, it's not too big. While steel threaded rod generally does have good strength, often small diameter common grades are made from steel that has a tensile strength lower than block masonry ladder wire. The simple solution is to use two pieces instead of one to ensure plenty of strength.
Very informative! Thanks for making this video.
Excellent Video. Thanks very much! In your example of a sink cut into the bench top, how would you have reinforced this? Cheers.
You are very welcome Tom! When you have a sink cutout, you still need to run the reinforcing all the way along the slab in a continuous straight line. So you reinforce the same but also add extra reinforcing in front of and behind the sink.
Thank you sir, explained very well... I appreciate your devotion....
You are very welcome!
What would you recommend for someone who is obsessed with learning this stuff, but has no experience in concrete, or construction, nor has the money to spend on a seminar or workshop, but wants to do this as a profession?
Thanks Neil! Please contact us via the website to address your question. This will require some engineering, but overall your thoughts sound on track.
Thanks for the numerous videos you guys have posted. They have been of great help. Im about to pour a 9ft x 3ft x 1.70'' thick countertop which I will then have to carry into place. Im wondering on the thickness of metal reinforcement I should use? Would 1/4" or 7mm be ok? Thank you.
Hi Jared. You're welcome! That should be okay. For a 1.5" thick countertop we typically recommend 3/16" reinforcement. Yours is a little thicker. There are more articles about reinforcement on our website: concretecountertopinstitute.com/free-training-category/reinforcement/, and we have a self-study course about it as well: concretecountertopinstitute.com/shop/reinforcing-101/
Thank you for this great video.
You are very welcome Jason! I'm glad you liked it.
great video - i suggest to others watching to set the speed to x1.5
A very informative video! I'm planning a counter top (60" X 30" X 2" slab) with a 2 inch over hang on 3 sides. Should I run the ladder wire from back to front (30") or lengthwise (60")? Thanks again for the great video!
Thanks, I'm glad it was helpful! this is a good question. You are thinking about where the stresses are in the countertop. You should definitely run the reinforcing lengthwise (60"). To be safe, it wouldn't hurt also to run it back to front (30").
Thank you Jeff, another masterclass that help me a lot!
I have a question, why my countertop curl or bend upside or I don’t know how to say, inside the mould? The facecoat is sprayed, and the back is GFRC. I cover the pice while curing, no matter if is for one day, or 5 days, the countertop curls on the extremes. After taking out the mould, the countertop is like a bridge, not a beam, is higher in the middle.
Any idea, any advice in order to avoid this big problem?
Thank you Jeff 😁
Curling is almost always due to differential shrinkage. Please see the section on Curling in the article concretecountertopinstitute.com/free-training/6-problems-with-concrete-countertop-mix-designs-and-how-to-prevent-them/
@@TheConcreteCountertopInstitute thank you Jeff!👍🏻
@@gonzalopmolina You are very welcome.
have watched numerous concrete countertop videos and am thinking about usein Quickcrete counter top bag mix, is this a good option or not I have about 85 ft. of countertop to produce in three different layers or height sections.
Hi Lee. As an engineer, my preference is for from-scratch mixes. However there are advantages, such as convenience, to using a bagged mix. For an article about this, please see concretecountertopinstitute.com/free-training/diy-or-bagged-concrete-countertop-mix/. If you do choose a bagged mix, I would advise one specifically designed for concrete countertops (such as the Buddy Rhodes mixes) rather than adopted from conventional concrete. Please be aware that there are many factors other than mix that are important for a successful concrete countertop project. For example concrete related factors such as not using too much water (concretecountertopinstitute.com/free-training/the-importance-of-water-cement-ratio-in-concrete-countertop-mix-design/) and proper curing (concretecountertopinstitute.com/free-training/curing-an-essential-step-to-create-high-quality-concrete-countertops/). Non concrete related factors include templating, forming and installation. Please see the articles at concretecountertopinstitute.com/free-training/ for all of these topics and more.
I learned a lot thank you very much.
You are very welcome Tyler!
Great video! Thank you for the valuable info!
***** You are very welcome!
So long story short use masonry remesh wire, 9 gauge? Run it longitudinal and latitudinal, how do you tie it in together? Weld?
If you make a 2" slab can you use regular 3/8" rebar? Or still too thick?
I'm doing an outdoor concrete countertop and I was wondering if I could or should use the block wire and the fiber glass together ,it will be two inches thick and i will be using 3/4 inch stone in the mix as well ,thanks for you help
If by fiber glass you mean AR glass fibers, no. Those are used as primary reinforcing in Glass Fiber Reinforced Concrete, whereas steel is used as primary reinforcing in traditional aggregate based concrete. You can use various types of fibers for secondary reinforcement to control plastic shrinkage cracking, but those fibers will not replace steel or provide/supplement structural reinforcing. Please see my blog articles about fibers: www.concretecountertopinstitute.com/blog/?s=fibers&submit=Search Curing is also a very important part of crack prevention, as is proper mix design and low water-cement ratio.
Great video! What is the best method of reinforcing inside corners for a L shape countertop?
Just treat the 2 ends of the L as 2 overlapping rectangles. Mix design is also important for preventing cracks on inside corners. You need a good mix design that has low shrinkage potential. Usually interior corners on sidewalks, etc., crack because the concrete has too high of a shrinkage rate. My mix designs are available here: www.concretecountertopinstitute.com/product-category/self-study-training/mix-designs/ And of course you have to cure properly too.
what is the process of making concrete ? Can you explain that with your primary sources please ?
great and very accurate explanation!!!
Thanks Andreas!
What if any reinforcement do you suggest with a fireplace hearth. dimensions are 24"x36" with 45 degree corners
Thank you
Planetary polishers are a fantastic tool that makes producing smooth, flat and gouge-free surfaces fast and easy. Justifying their cost (and the tooling - in triplicate!) is something you need to determine. Do you do a lot of large, flat countertops? Do you or your employees struggle with keeping a single headed polisher flat? If so then maybe a planetary polisher is a valuable asset. You will still need a single-headed polisher for narrow sections, edges and inside integral sinks.
great video, thanks for sharing!
Great vid
(other than the audio only on one side. Did you know that you can re-upload a new audio track to the same video, and this way you could fix it?)
Sorry about that, and thanks for the tip!
great video ... how far in from the edges of a worktop should the ladder mesh run? i.e. if i had a 2400 cm worktop ... what length would i cut my ladder mesh to? thank. doug
You should run the reinforcing as long as possible. You need only about 6mm of cover, so you can go that close to the edge.
Cheers!
I am building a 1.5" x 4' x 5' slab for an outdoor kitchen. They will be supported by a 5' x 32" cabinet base. Do I run ladder wire close to the bottom of the slab depth along the 5' length direction for the Simpson's beam stress and another run of ladder wire along the 4' width direction for the cow cantileaver diving board stress? If I do this properly, do I also need corbels to support the 16" overhang, or is the integral ladder wire enough?
Joe, I love the terminology "Simpson's beam stress" and "cow cantilever diving board stress"! LOL!
Yes, the 5' length ladder wire is on the bottom of the slab, and the 4' length is on the top. You likely don't need corbels because you've got a 2 to 1 ratio of supported to unsupported, so you don't have a tilting problem. However, corbels never hurt, and they can be a decorative feature.
Glad to bring you a laugh. One follow-up: your 3 hour intro seminar says not to vibrate after reinforcement goes in because it can sink or cause ghosting.
I'm not worried about sinking because I'll suspend reinforcement from strings, but since the cantileaver reinforcement goes 1/4" from the bottom of the form, how do I vibrate? Do I pour less than 1/4" of concrete, vibrate that, set the reinforcement in place, then pour in the rest of the concrete?
You are correct, Joe. Also make sure the reinforcement is well supported/suspended so it doesn't move around during vibration. Or, you could avoid the issue completely by using a stiff, hand packed mix or by using GFRC.
Jeffery,
Does it matter what type of concrete to use? Can I use regular concrete or do I need specifically concrete countertop mix??
Good question Brice. Just like reinforcing design, concrete countertop mix designs are specialized for the application. Please see this page for more information: www.concretecountertopinstitute.com/blog/2015/08/concrete-countertop-mix-design-principles/
Thanks , My need is to know for a 3 inches slab or counter top, what the size of iron bars should i be using. Secondly we are familiar with milimeters rather than using gauge, so for 8 & 10 mm bars how to convert to gauge, Thank you sir
For a 3" (76mm) slab, you should use standard #3 rebar, which is 3/8" or 9.5mm. So 10mm would be fine if that's what you can get. The 9-gauge ladder wire you see in the video is appropriate for thinner slabs, 1.5" (38mm) thick.
Thank youSir, very helpful will go by the 10 mm. Thanks
Excellent explanation. I need to make a very thin rectangular countertop, say 19 mm thick x W=800 mm x L=900 mm supported at the perimeter. Can it be done? how? Thank you!
For this large, thin application, I would use GFRC instead of traditional precast. Please visit our website at www.concretecountertopinstitute.com/blog/2015/08/index-gfrc-concrete-countertop-training-free-information/ for extensive GFRC information.
how does basalt fiber reinforcement compare to gfrc? also what about a carbon or fiberglass mesh instead of ladder wire?
Wow! This was a very educational and interesting video! :)
Great video! I am trying to make my first concrete countertop that I'm wanting to make 1.5" thick. If I am putting my WWF near the bottom of the slab, how much concrete cover do you recommend? I feel like anything less than 3/4" of cover will result in ghosting or the concrete spalling off?
Kyle Sievers You need only 1/4" of cover. That will achieve enough of a bond to hold the steel in, and it won't cause ghosting. See this article about the causes of ghosting: www.concretecountertopinstitute.com/blog/2012/10/how-to-avoid-ghostlymistakes-in-your-concrete-countertops/
Perfect! So what do you recommend around sink knockouts and other openings if #3 rebar is too large for a 1.5" countertop??
Kyle Sievers You should use masonry block ladder wire, 9 gauge, or 0.147” (3.7mm) in diameter, throughout.
There is no easy rule of thumb for the necessary spacing, because stresses vary depending on the geometry of the slab. However, you're usually safe with a spacing of about 6".
Near sink holes, you will add reinforcing on the *opposite* (top) face, as if it were a cantilever. Remember, outlining the sink holes does no good - you should run the reinforcing in the long direction.
Great info, great video Thank You.
You are very welcome.
awesome video man, two thumbs up!!
could you tell me about the lighting used for this video
This might be a little off topic for counter tops which I am interested in. I am also interested in applying this to build a thin shell concrete dome workshop using basalt rebar and mesh. Do you have any thoughts about applying this to a small to medium size dome shaped workshop? Thanks!
+Robert Miller Hi Robert, sorry for the delay in replying to you. This is indeed far removed from countertops (thin slabs supported by the ends). I recommend that you get specific advice from a structural engineer, particularly because people will be underneath this structure.
Yes I will absolutely get advice from a structural engineer before I build. If for no other reason than to save money from grossly over building. I was just curious about what you thought in general. Perhaps what you know about the strength of a well built 1 1/2" or 2" counter top using basalt rebar and mesh.
I'm at least a full year before I'd build anything. I'm just thinking out loud so to speak. Thanks!
I have learned a lot about Concrete counter tops. I'm an old laminated counter top guy myself. This is way better!
How in the world did you get that giant slab to flex under so much pressure? I didn't know concrete was so flexible!
Hello Raskal Robbin. It looks like you may be the same commenter who asked about fiberglass scrim. I have combined my answer to both questions in my reply to the fiberglass scrim question.
Easy to understand it :) Thank you
Great Video!!! On your beam 8' x 6" x 1.5" beam did you use the 9 gauge structural wire?
Yes, that's correct.
Just out of curiosity, what would be the absolute thinnest slab that you could make with GFRC reinforcement that would stand up to at least a 300 pound load?
+kobudo, That's impossible to say without knowing the dimensions of the piece, how it's supported (just on the ends or on a solid substrate), and whether this is a point load or would be distributed across some area.
The Concrete Countertop Institute About 18" x 8", supported under the ends of the 20" span, with a 300 lb. point load at the midpoint.
Just curious.
1.25" is the minimum thickness I'd recommend. However, this is pretty close to the working limit of the slab, so to be safe I'd cast it 1.5" thick.
Thanks pretty good video . I would like a little more info on how ya do the installation. I'm a new contractor investing my time into this business venture. I've been in stamping concrete for pools and driveways since before it became big and people started doing it. I'm now on my own and disabled and want to try doing countertops for my house and a couple of friends of mine. So i'm no rookie by no means to stamp crete lol.
Hi Richard, sorry I missed this. Please see this article about installation: www.concretecountertopinstitute.com/blog/2014/02/installation-important-countertops/
Countertops/sinks/fireplaces/etc. are a great way to be creative with concrete without the backbreaking labor involved in flatwork and in the comfort of your own shop. Best of luck with your venture, and I hope that CCI can be a part of helping you succeed. Please don't hesitate to contact us at info@concretecountertopinstitute.com.
We are building a concrete countertop for a kitchen island. It is 1-1/2" thick, 4' wide and 7', 2" long it will have a 9 inch overhang on the long edge. We are using ladder wire for reinforcement. Do we need to build 2 separate reinforcements for this or can we simple use one and add extra ladder wire where the overhang will be? We did build 2 separate ones but the one closest to the form (finished surface) is only 1/4" from the form. my concern is that it is too close to the surface and we have too much reinforcements.
I'm no expert but it sounds like two sets of reinforcements are required: one length wise (ladder wire near the bottom), and one set width wise (near the top) for the cantilever of the overhang.
(2) According to the video, reinforcement closer to the center is less effective, so further out is better, but where's the limit? How close to the surface do you want to be?
Hi Matt, sorry I missed this. Hugh is right, you do need one length wise near the bottom and one width wise near the top for the cantilever. The cantilever reinforcing can be 27" long (twice the length of the overhang). It doesn't have to be as dense as the regular reinforcing. 9" is not much of an overhang and probably not an issue unless somebody really heavy is going to be sitting on that edge.
1/4" from the finished surface is fine. 3/8" would be the maximum, and the minimum is right at the surface. Please see this article about ghosting: www.concretecountertopinstitute.com/blog/2012/10/how-to-avoid-ghostlymistakes-in-your-concrete-countertops/
I doubt you have too much reinforcing. It's better safe than sorry. Too much would be so much that there's more steel than concrete.
Very Informative.
Thank you
Wooden tops on the cabinets will not provide structural support. Wood is too flexible and weak, so you still need the proper steel reinforcing in the concrete. The dimensions of the cabinets are fine - the concrete countertop will lay over top of several cabinet boxes, depending on the layout of your kitchen.
I'm confused about the sink cut out part. Shouldnt each section supported on 2 points by the cabinets be considered its own beam and not be effected by the sink cut out?
Reinforcing a piece is done more for safe handling and transportation, rather than for after the piece is installed. Since the slab is handled as a single piece and is likely lifted from the ends, the entire slab needs to be reinforced to resist the bending forces imposed on it by its own weight when it's lifted. It will be subject to less stress once it's on top of the cabinets and supported by the cabinets at 2 points as you mention.
The reinforcing runs through the whole piece because the weight from two "wings" that are adjacent to the sink hole place a great deal of stress on the long, narrow sections that form the sink hole portion of the countertop when the piece is lifted and moved. Reinforcing has to be selected, located and placed accounting for the greatest stresses expected. When reinforcing adjacent to a sink hole, you add extra strands all the way along the length of the slab through the very narrow sections in front of and behind the sink hole.
Fiber glass mesh vs wire mesh vs fiber
Which is the best and why. I understand fiber glass is the easiest which will give you the best strength? Should you use 3/4" plywood as a backer? What is the best way to strengthen the thin strip in front and behind the sink people are always sitting there..
With all of the terrible videos done by people who know nothing, its nice to find a video with a guy who knows what he is talking about. Great video.
Thank you @H2oways!