Warped boards and what to do

[Marty Leenhouts]

I’ve been asked this question several times…

Q: Hi, do you have any suggestions on how to take a warp out of a board this size? I may have seen it on your website before but was unable to locate it. Would appreciate it.  Thanks,   Rick 

A: Hi Rick,
The side that is cupped is drier than the other side. Moisten the cupped side and place it cupped side down in the sunlight. You can speed it up by using  hair dryer on the non-cupped side.
Repeat as needed until flat.

Marty,
I’ve attached a picture of my warped board.  Again, this has been carved and sealed with two coats of sanding sealer.  Can you think of any means by which to salvage this?  I do plan to put rubber feet on the bottom corners, so it doesn’t need to be perfectly flat, but at least enough so it’s not so obvious, and especially on top where the chess pieces will go.

A: Very wide, thin boards like this are going to cup/warp. As wood sits in any environment it takes on and gives off moisture. Naturally the more humid the air is the greater this moisture exchange will be. Wood is composed of cells, think of them as little tiny balloons. As the wood takes on moisture the balloons expand causing the wood to expand. As the other side doesn’t take on the same amount of moisture and the same rate, those balloons will be a different size. The larger balloons make the surface area larger causing the wood to expand. The drier side with smaller balloons will contract shrinking the surface area. This drier side is the cupped side.

To “fix” warpped boards, try to even out the moisture content on both sides. Add moisture to the cupped side to expand the balloons while at the same time drying the other side to shrink the cells. Adding weight to one side and heat to the wet/expanded side can speed up the process. It takes some experimenting and patience.  But even after the board is flat it can warp again as it takes on and gives off moisture. Sealing the wood may help but it’s not the cure-all. Some type of frame can help keep the board flat.

Adding sealer to a thin board will drastically change the moisture content of the cells and cause immediate changes. Sealing both sides at the same time will help but may not stop the change from happening. Avoiding the sealer and just applying a clear top coat is a better approach as this avoids changing the moisture content of the wood.
Marty

[William McHugh]

Thanks, Rick for posting a question I continually raise with others. Marty has been patient and responded to  my  questions twice. His explanation above is clear and concise; perhaps it will sink into my brain this time.

P.S. I, too, used the sanding sealer on a practice board I had carved – with the same result you had. I have been told by some carvers that the wood has to be a minimum of 1/4″ thick to avoid such warping. I have used sealer on wood 1″ inch thick with no warping but do not know how much lower you can go.

[Aeroclassics]

Wide thin boards are guaranteed to cup or warp. Even though the board is all one piece it will absorb moisture at varying rates depending on the time of the year. This is why table tops etc. are usually made up of boards not more than 4” wide. Sealing helps but on very thin boards can induce warping as the sealer may not be absorbed at the same rate.

Marty made a good suggestion about wetting the cupped side. Since you have sealed the board I would try laying a damp towel over the cupped side and use a warn iron to try and remove the warp. I would also find a way to clamp the board after ironing so that it is “over bent”  as that may help compensate.

Doug

[Paul1780]

I also use sanding sealer. I use Zinsser brand and thin it about 1:1, this gives me some shellac with a lot of drier in it. Next I apply the sealer to the uncarved side and let it suck it up. This will dry fast with all the drier in it. When dry to the touch (2-3 minutes) l do the carved side, If you think about it the carving gives you a ton of end grain so sealer will be absorbed big time. There is your imbalance on both sides.  Conclusion: by applying the smooth side first you are introducing the moisture to the side less likely to cup first(giving it a head start). When the sealer goes on the carved (end grain) side it will be pulling against the 1st wet side hopefully evening out the tension a bit. After the sealer is on there I let the project sit a day or two to give the solvents a chance to dissipate. l find the addition of the thinned sealer on my carving closes up the intersecting cuts nicely and makes for better results. Hope this helps.

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