FLAT SLAB DOORS WHAT'S UNDER THAT VENEER?

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[@clivewilliams3661]

Mdf (medium density fibreboard is widely available in Europe including DiY stores (Home Depot style). It has its limitations although it is dimensionally stable it is not a panacea material. It should be recognised that its dust is carcinogenic and the appropriate PPE is vital. Apart from Mdf there is also Hdf (high density fibreboard) that is more robust. It is one of a range of panel materials that can be used and each one has advantages and limitations so that to use any requires knowledge and correct selection. Mdf is often used for cheap furniture with laminate or veneer finish.

[@theoriginalwoodchuck]

Thanks for the information. I'll be looking into "HDF" as it's never mentioned here in the States. I always thought though that Ikea and such use Pariticle board core for their products, not MDF. I guess if it's an 1/8" back, possibly.

[@clivewilliams3661]

@@theoriginalwoodchuck The kitchen suppliers often use particle board (chipboard) as a core for their laminates but it has a reputation for disintegration and swelling when wet. In UK we commonly used chipboard for flat roof decks and I have seen that construction of brick garages in very dry summer weather culminated in the brick parapets being pushed off in the winter as the deck absorbed atmospheric moisture and swelled, the force is huge.
Whether you have Mdf, Hdf or chipboard in panel furniture depends on the quality of the product and the price point. Mdf and Hdf both have the benefit of being able to be press moulded into decorative panels. The back panel of cupboards tends to be hardboard, a pressing of paper that will have an oil tempered surface to provide an ultra smooth finish, which has a paper decorative laminate. Thin 1/8", 3mm chipboard is never a good idea as it crumbles at the edges if worked, although I have seen it used
On one job we had oak veneered panelled Mdf fire doors for an upmarket refurbishment for a wealthy client. The fire doors were certified as 30mins or 60mins and it is unlikely that we could have achieved that fire rating as a panelled door in solid oak. The other benefit if Mdf was that it was very stable with no potential for warping or shrinkage that plagues most solid doors. They came as fitted doorsets that were simply fixed in the opening although that meant that there was no hope of easing the door at any stage as it would destroy the veneers.

[@clivewilliams3661]

@@theoriginalwoodchuck Particle board aka chipboard is used extensively in flat furniture panels with either a veneer or laminate finish although some suppliers now use Mdf as a core. Chipboard has a reputation for disintegrating when wet with significant swelling of the board. I have seen chipboard used for flat garage roofs where it was laid in a hot dry summer and by the winter the boards had pushed off the brick parapets, such was the force in swelling under atmospheric moisture.
Most panelled furniture use an oil tempered hardboard as the rear panel as this give a very smooth finish, which is often then finished with a paper laminate. I have seen 1/8" (3mm) chipboard used but it isn't suitable although easier to work.
I have used Mdf as the core material for some very upmarket oak veneered panelled fire doors in 30mins and 60mins certified rating for a wealthy client. It is unlikely that we could have achieved those ratings with a solid oak panel door. The other benefit of the Mdf cored doors is that they are dimensionally stable with no potential for warping or shrinkage. They come in fitted doorsets that just require fixing into prepared openings. This does mean however, that they cannot be eased in any way due to the veneers on all edges.

[@HugeHugsNow-vx5cn]

Thanks Chuck for that insight. What does the client desire, painted or just a clear finish on it?
Have you found that longer (taller) MDF core doors have a habit of warping over time?

[@theoriginalwoodchuck]

There's always a risk with tall doors, I think MDF is the most stable though. They'll have it painted. Thanks!

[@clivewilliams3661]

Mdf is unlikely to warp naturally, if it does then it is more likely the applied finishes that are causing differential tension (including paint). Note that using Mdf as door will require the fitment of hinges that are best not fixed through the edge rather the face and check with the fixing suppliers to get the best fixing for the material.

[@theoriginalwoodchuck]

Thanks. Agree on the finishes. So to clarify for others- Fixing through the edge of the door especially only 3/4" thick can split the MDF as there's not much material surrounding the screws and the fibers are not the best for holding power. I would use course threaded screws if possible in my opinion. SOSS hinges generally are mortised in the edge of the door.

[@clivewilliams3661]

@@theoriginalwoodchuck When fixing into the edge of Mdf is to drill a fixing hole, the core size of the screw and fill the hole with wood glue before you drive the screw in and definitely don't over tighten. Its not for heavy duty work but can be used to lightly hold two panels together.