warped flooring query

[Tim_H]

I am making some flooring for my workshop from t&g chipboard with some thin strips of oak laminated to the top ( to match the appearance and thickness of some salvaged solid wood flooring I have down.

The oak is,about 5 mm thick and glued on in 50 mm wide strips with Titebond 2 and finished with boiled linseed oil. All was going well until I noticed it was bowing up at the edges. I assume this is due to the moisture warping the oak from the boiled linseed oil on the upper surface only.

I have been able to flatten it out with clamping over a small batten but wonder if anyone has any suggestions on how to avoid it happening if I make more ( which I will need to to cover the area) ?

Constructive (pun intended) advice appreciated, although I suspect I might give myself the advice from the old joke "if you want to get there, I would not be starting from here!".

Thank you.

 

[Sgian Dubh]

You've created an unbalanced lamination. I'm guessing the distortion shows in two ways in that the boards are concave (cupped) across the width and bowed in the length, in both cases towards the oak face.

In most cases when creating this sort of structure what you put on one face needs to be repeated on the other to keep the structure in balance, e.g., veneer both sides of a ground to make a panel, apply equal amounts of polish to both sides of the table top, etc. There are exceptions, and if you look at engineered flooring for example, you'll notice that different materials are usually used on either side of the board: in those cases the manufacturer has worked out how to keep them reasonably stable and flat.

In your case, my suggestion would be to put an equal thickness of oak on both sides of the chipboard. To keep the overall thickness you have already made that would suggest putting wood 2.5 mm thick on both sides. Surprisingly, perhaps, you wouldn't necessarily need to put relatively expensive oak on both sides, and the back (hidden) face could probably be covered in something cheaper, such as poplar (tulipwood). Even though this is not the same species and has different shrinkage characteristics, and other properties to the oak, it's likely to be able to keep things in balance. Slainte.

 

[Chrispy]

If you are up for experimenting you could try sticking with the same glue as you use for the oak a thick brown paper to the underside the kind used as floor protection or under carpets, doing this will at least balance out the effects of the glue shrinking as it dries.

 

[Tim_H]

Thank you for that, really helpful.

I will experiment with both those options.

I am getting some more wood off cuts shortly so could try the thin oak and thin backing Tulipwood option.

Would I be right in assuming that a thinner veneer would be less likely to bow anyway?

 

[dickm]

Not sure I agree with the diagnoses above. it's the "veneer" which is bowing (and presumably pulling away from the chipboard?) not the whole one-sided sandwich as I read the OP. Isn't it more likely to be change in M/C of the solid timber, either from moisture coming out of the floor (is there a DPC?) or from moisture loss to the air? (There shouldn't be any moisture in the linseed oil) Putting a balancing veneer on the other side of the chipboard won't help if it's just diferential moisture change in the veneer. But the effect would certainly be less with thinner veneer.

 

[Tim_H]

Sorry if I did not make myself clear, the veneer is not pulling away, it is the whole sandwich that is bowing upwards.

 

[dickm]

OK - my mistake. Apologies.

 

[Sgian Dubh]

Would I be right in assuming that a thinner veneer would be less likely to bow anyway?

Not necessarily. The result of using a thin veneer on just one side instead of a thicker one may (or may not) be less pronounced, but cupping and bowing are still likely. But as I said in my earlier post we generally try to keep things in balance, so if I used a thinner veneer on one side I'd still aim to attach something similar on the other side for balance. I've seen many examples of people trying to get away with what you've tried: I can't think of any examples where the experiment has succeeded, unless there has been some sort of additional reinforcement to counteract the imbalance. A simple example are chess boards veneered one side only- they're always dished horribly, and pretty much a failure. The same applies with tea trays veneered on just one side, etc.

I mentioned earlier too that there are exceptions, such as the laminate flooring example I gave, and further examples include drawer fronts and carcass sides veneered only on the show face. In these examples, whilst I've seen cupping and bowing from time to time, for the most part they've survived pretty well. The reason for this is that there are structural elements on the unveneered side to help hold the piece flat, e.g., corner joints of drawer boxes, and carcass sides similarly feature corner joints and there's usually reinforcement in the form of runners, kickers and the rails that join the two carcass sides together. Slainte.