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I'm trying to make floor tiles which should look similar to attached picture. I sliced a wood about 6mm thick and wanted to glue them to the mdf base. However when I put PVA glue on a wood slices, they bent. Corners of slices raised from a base from 3 to 7 mm. Bending is really huge and caused by the moisture of glue. So with such a deformation gluing is not possible at all. I tried to straighten slices with a board on top of them and clamps but only crack a couple of them.

So the question is how to prevent wood bending? or is there other way to attach slices to a base?

Thanks.

PS: as mentioned in comments, each tile is supposed to be a rectangular about 800x400mm, these sizes could vary. Slices (open grain pieces) are going to have width about 60-85mm (85 is the capability of a saw) and length 60-100mm.

enter image description here

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  • that is an awesome design and an awesome picture. It has inspired me to want to put that somewhere in my house. I am very interested in what the results of this Q&A and process will be. I am sorry this comment isn't helpful. Would it be possible to glue up the full length boards first and the slice them to the tile size? Is part of the issue with the glue up being smaller/thinner pieces? – Keith E. Truesdell Apr 5 '18 at 13:40
  • @user3124812 I have two thoughts for you. 1) use weight to keep the tile down until the glue is dried. Maybe concrete bricks would do the trick. My thinking is the brick will keep the corners down (if it is spread through the whole thing) until the glue hardens. Once the glue hardens the brick can be removed and it should be like the picture. The other thought I have is to use a brad nailer around the corners. I am not super at metric but maybe you can get in from the side to hole the corners down. I was going to say shoot through the top but that might not look very good with nails through... – Ljk2000 Apr 5 '18 at 13:56
  • out the floor. I did not want to answer as a question because I don't think this is the best solution, but maybe it is. The project looks amazing, hope it goes well for you :) – Ljk2000 Apr 5 '18 at 13:58
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With thicker blocks you could use PVA but don't, it's the wrong sort of adhesive for the application*. Whatever glue you pick must be completely waterproof — these are fairly thin end-grain blocks you're attaching, so will be extremely permeable to water (basically like sponges).

You could I suppose use mastic or construction adhesive but there are numerous purpose-made flooring adhesives and some will be suitable.

This type of thing used to be done using bitumen or a bitumen-based adhesive and they are still considered a great choice by some pros, but I'm not sure if they'd be available where you are. However they are still made and available from the right suppliers, in Europe at least.

In theory at least you could use epoxy for this, as epoxies don't contain any water they don't cause wood to swell. However it will work out very expensive if you have a large area to cover. And if it matters, the cured adhesive is so strong it could make removal of the flooring at some point down the line a real nightmare. Even cleaning excess adhesive out from the grout lines could prove a real challenge!

*No gap-filling ability, to allow for irregularities in the sub-floor or the wooden blocks themselves. Many simply won't be waterproof enough. They don't bond end grain well without prior preparation so would add hugely to the effort needed to complete the project (every block would have to have glue spread on it twice).

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  • I'm not attaching slices straight to the current floor, mdf pieces are going to be used as a sub-base. About adhesive, a fast search gave that there are some Bituminous Adhesive (bunnings.com.au/…) and construction adhesive (bunnings.com.au/selleys-350g-heavy-duty-liquid-nails_p1210564). Do you mean stuff like that? – user3124812 Apr 5 '18 at 14:59
  • Yes and yes, although the roofing stuff is not specifically made for bonding wood so you might want to test it out before committing. Re. using MDF as a sub-floor, presume you're intending to use MR MDF? – Graphus Apr 5 '18 at 15:13
  • yeap, moisture resistant. BTW it's going on top of current ceramic tiles like a second layer cover. I believe moisture isolation is not the biggest issue in such a case. Also it is the reason I want to have tiles relatively thin. Thanks, construction adhesive looks as attractive solution. – user3124812 Apr 5 '18 at 15:34
  • Loctite PL Premium is the go-to adhesive for wood in such situations, because it contains no water, thus not causing issues with cupping. Another option is hardwood flooring glue, which might be even more suitable. – Eli Iser Apr 5 '18 at 18:19
  • I end up w/ Selleys polyurethane construction adhesive (Loctite is not widely available in AU). On a tested pieces it did the job very well. No wood bending/cupping and a good bond. Thanks guys. – user3124812 Apr 8 '18 at 12:15
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This is tough because you're gluing end grain, which is notorious for soaking up a lot of glue. Using too little leads to a weak joint, but using too much can cause problems as the moisture escapes unevenly (as you've discovered).

Put clamps on when you apply the glue. You can clamp each piece down individually with multiple clamps, or use a couple cauls to apply even pressure on each piece. Or, depending on the size, put another piece of mdf or plywood on top and clamp that to the base (using cauls to get clamping pressure in the middle if needed). You may not need clamps at all, and a heavy object (book, bricks, paint can, etc) on top of a board may provide enough pressure to keep the tiles flat.

You may be able to only glue a few pieces at a time this way, as PVA glue does not have a long working time.

One possible alternative would be to use epoxy and do this in two passes. First, put a thin layer of epoxy on the bottom of the tile to seal up the end grain a bit. Let that dry / cure, and then use another layer of epoxy to adhere the tile to the MDF base.

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  • I tried clamps, they didn't work at all. I put a wide board on top of 3 slices (total length about 20cm) and pressed it hard with 2 F-clamps. Result 2 slices had 3 corners glued and 1 corner in an air, the last slice got 2 corners glued to the base and 2 raised. When I tried 2 F-clamps on one slice, it breaks through the center... Will try epoxy over weekend. thanks. – user3124812 Apr 5 '18 at 14:46
  • Graphus is correct about the type of glue. That said, the problem with the clamping is a separate problem. Use cauls to spread the clamping pressure more evenly and prevent having one corner glued down while the other is in the air. You will probably find you want to do this even if you are using epoxy. – Katie Kilian Apr 6 '18 at 17:12
  • Either that, or use Ljk2000's suggestion of adding extra weight on top. Sand bags work great for this. I use unopened bags of kitty litter for this sometimes, when I have it available. – Katie Kilian Apr 6 '18 at 17:13
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The wood is curling due to moisture before the glue can set. If you must use PVA glue, try wetting the top side with water and cover the top with plastic sheet to slow down drying of the top. You may have to sand the top surface for any grain rise, but you will needed to level the tops anyways

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  • I tried this way before posting this question. Wetting helped to keep slice straight and glue full surface to the base. But slice bent after drying and in fact slightly bow a mdf base. – user3124812 Apr 8 '18 at 12:19

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