How to "un-warp" wood?

[Rob Luter]

We had a little water crisis in the basement, and a walnut silverware chest wound up sitting on wet carpet for at least a couple days. The chest is box joint corner construction and the bottom is a panel made from three edge glued pieces that were subsequently glued to the bottom of the box frame. Most of the glue joint between the bottom panel and the chest frame let go, and the panel curled up in a big way. All the edge glued joints are fine.

Is it possible to flatten this out? I thought about a good long soak in hot water and then flat clamping between a couple of sink cutouts faced with laminate until it dries out. If the edge joints let go I can always re-glue.

Thoughts? Comments?

[Thomas Pratt]

My suggestion is that the bottom soaked up a lot of water to warp; therefore, you could possibly put the wood in a low humidity, warm air environment. Perhaps an air tight bucket with a lot of reconstituted silica gel. Just maybe the wood will remember to go back to where it was. I am just guessing, so let me know if it works.

[John TenEyck]

If the panel was just glued to the bottom of the box and has now mostly let go, I'd be inclined to try to remove it completely. Once you have it free you can try to flatten it, but if that fails, you could make a new panel. Somehow, a panel of solid wood glued onto a box frame just sounds like a recipe for failure, water bath or not. I wonder if the original was glued only near the center of the panel, and that's why it pulled away so easily when it got wet.

John

[Eric Commarato]

You might try placing the warped wood on your lawn for a couple hours on a warm humid sunny day, I would assume the bowed side down. I've heard this works, but have never tried it. If anyone else has heard this please chime in.

[Doug Hepler]

Rob

Don't wet the drier parts. Dry the wetter parts. It might flatten

Doug

[Wade Lippman]

The ice maker in the fridge broke and flooded the kitchen. The flooring cupped. A few months later they went pretty much flat again. So if you are patient... (YMMV)

[Doug Bowman]

You might try placing the warped wood on you lawn for a couple hours on a warm humid sunny day, I would assume the bowed side down. I've heard this works, but have never tried it. If anyone else has heard this please chime in.

My father did this several times when refinishing and restoring furniture. It works

[Rob Luter]

Rob

Don't wet the drier parts. Dry the wetter parts. It might flatten

Doug

It's dry as a bone now. I popped the remaining glue joint off last night. I think I'll try wetting it and pressing it out. It cupped on the wet side originally. Maybe I'll wet the convex side, maybe both. It's not an heirloom, so if it fails miserably I'll just make a new bottom.

[Wayne Lomman]

Force drying is a no-no. It risks splitting the timber. At best, wet the concave side until you get it to straighten if it will. If it won't, rip into its planks, dress them again and remake it. Or make a new one. Cheers

[Robert Engel]

It's dry as a bone now. I popped the remaining glue joint off last night. I think I'll try wetting it and pressing it out. It cupped on the wet side originally. Maybe I'll wet the convex side, maybe both. It's not an heirloom, so if it fails miserably I'll just make a new bottom.It will be a good experience dealing with this problem.

FWIW I seem to get better results wetting the concave side rather than drying the convex.

Be sure to use spacer sticks when clamping to provide air flow. Clamp it up for a few days and see what you've got. I would be optimistic.

[Doug Hepler]

Rob,

My reasoning is that if the panel was flat before the flood, it will flatten again when the sides are equal in length, i.e., equally dry. The reason that you should not wet the dry side is that it will eventually have to dry again, when it will shrink. Why chase your tail? Like Wade, I counsel patience

Doug

[Rob Luter]

Rob,

My reasoning is that if the panel was flat before the flood, it will flatten again when the sides are equal in length, i.e., equally dry. The reason that you should not wet the dry side is that it will eventually have to dry again, when it will shrink. Why chase your tail? Like Wade, I counsel patience

Doug

I understand where you're coming from, but both sides are now equally dry, and have been for days. Since I made my original post, my understanding of the mechanics of cupping has changed, and suggests that only a good soaking and forced flattening will work. Let me explain. Years ago I built a deck. Logic at the time dictated that I orient the deck planks such that the rings on the end grain arched up. I was told that any cupping that would occur would cup towards the concave side of the rings and the boards would always shed water. In reality, just the opposite happened. I always wondered how I screwed that up? In any case, I was watching a YouTube in the last couple days where the mechanics of cupping was explained as the growth rings trying to straighten out, therefore, the convex side of the rings would ultimately become the concave side of the cupped board. Looking at the end grain of the panels that formed the bottom of this box, that's just what happened. The three component pieces that make up the glued panel have their rings oriented the same way, and the cupping occurred on the convex side of the rings. Counter intuitive for sure.

[mark mcfarlane]

I understand where you're coming from, but both sides are now equally dry, and have been for days. ...

Being dry on the surface, and being uniformly dry throughout the thickness of the wood, are two different things. Air drying times for wood seem to be measured in months or years, not days.

How thick is the walnut bottom? Do you have a moisture meter that can measure below the surface of the wood?

[Jeff Duncan]

If you do try to press it out don't use laminate, it won't allow the water to escape so panel will stay wet for a loooooong time. Ideally you would want to press it allowing for maximum exposure to dry evenly. May be difficult to do. Alternatively you could press between two flat sheets but have some material that will absorb the extra moisture.....essentially what is done with veneers before gluing. I don't know if it will work.....but only one way to find out;)

good luck,
JeffD

[Rob Luter]

Being dry on the surface, and being uniformly dry throughout the thickness of the wood, are two different things. Air drying times for wood seem to be measured in months or years, not days.

How thick is the walnut bottom? Do you have a moisture meter that can measure below the surface of the wood?

The bottom panel is 1/4" thick. I don't have anything I can measure moisture content with.

[Rob Luter]

If you do try to press it out don't use laminate, it won't allow the water to escape so panel will stay wet for a loooooong time. Ideally you would want to press it allowing for maximum exposure to dry evenly. May be difficult to do. Alternatively you could press between two flat sheets but have some material that will absorb the extra moisture.....essentially what is done with veneers before gluing. I don't know if it will work.....but only one way to find out;)

good luck,
JeffD

I figured I'd use something firm but absorbent. I'll probably line the laminate with paper or cloth so it will wick the water out of the wood.

[John K Jordan]

...Logic at the time dictated that I orient the deck planks such that the rings on the end grain arched up. I was told that any cupping that would occur would cup towards the concave side of the rings and the boards would always shed water. In reality, just the opposite happened. I always wondered how I screwed that up? ...

Rob,

It sounds like someone gave you advice based on ignorance. The way boards tend to cup certainly is counter-intuitive until you understand how wood shrinks as it dries.

Since wood shrinks more in the tangential direction than the radial direction, all things being equal a board will cup towards the convex ring direction as wood shortens along the ring. This picture shows some typical shrinkage of pieces cut from various places in the log cross section.

http://www.furniturelinkca.com/images/softwood_4.png

Imagining that the growth rings are trying to "straighten out" may be a simplistic way to remember this but understanding the way wood shrinks is far more useful since you can apply it to all possible cross-sectional orientations. The tangential shrinkage is often close to twice the radial shrinkage. (Shrinkage in the long grain direction is usually insignificant.) If you look up "T/R ratio" you can find charts of typical shrinkage ratios for different species. The fact that wood shrinks less in the radial direction is what makes true quartersawn lumber less likely to warp.

Note that the T/R ratio does not tell the entire story when trying to predict shrinkage and warping. The total shrinkage of the wood species is important as are other properties of the wood. Some species are inherently more stable than others. Also, when considering the entire board, the simple cross-sectional T/R ratio must be considered along with the way the board is cut from the log relative to the long grain. For example if the board is not perfectly aligned with the grain relative to the pith (almost always the case) the board can twist, bow, or crook. Also, stresses in the wood from things like the tree growing at an angle to vertical can create "reaction wood" and the warping from that can overshadow other factors. The way the wood is dried can also cause internal stress and warping.

Anyone who works with solid wood can benefit from learning how wood behaves. My favorite reference is "Understanding Wood" by R. Bruce Hoadley. The author is not only a wood scientist but a a craftsman with real-world experience.
https://www.amazon.com/Understanding-Wood-Craftsmans-Guide-Technology-ebook/dp/B004WYO862

As for unwarping, I always apply moisture to one side somehow. Just last week I flattened a cutting board that had somehow cupped badly. It was completely dry. I dampened the concave side, stuck a wet paper towel to that side, then set it back on the counter with the wet side down. In less than a day it flattened perfectly. I propped it up to dry completely and after a week of use it is still perfectly flat. If it was not, I would have repeated the process as needed with decreasing moisture each time.

I have also been successful many times flattening boards by laying them out on the grass with the cupped side down, preferably out of the sun unless I'm in a hurry. The bottom side picks up moisture from the ground. I don't know if I'd recommend this for fine lumber intended for joinery.

JKJ

[mark mcfarlane]

The bottom panel is 1/4" thick. I don't have anything I can measure moisture content with.

Using the 1"/year rule of thumb for green lumber, that's 3 months to fully air dry 1/4" stock, depending on how saturated it was and the temp/humidity in the area where you are trying to dry it. It probably won't take quite 3 months, but a few days or weeks also probably isn't enough. Someone with more experience air drying may chime in...

[John K Jordan]

Using the 1"/year rule of thumb for green lumber, that's 3 months to fully air dry 1/4" stock, depending on how saturated it was and the temp/humidity in the area where you are trying to dry it. It probably won't take quite 3 months, but a few days or weeks also probably isn't enough. Someone with more experience air drying may chime in...

My experience is wood 1/4" thick will air dry very quickly, perhaps even in a week or so depending on the species and what it is finished with, if anything. One way to check is carefully weigh the board. Then weigh it again after some time, maybe a week for something this thin, repeating if the weight has changed at all. When the wood has quit losing weight it is at equilibrium with the environment.

JKJ

[Rob Luter]

@John K Jordan - Thanks for the thorough response. The graphic was especially useful. The uppermost example is what is happening, and what happened on my deck boards. I'm glad I use Quartersawn wood on almost everything I build.


http://www.furniturelinkca.com/images/softwood_4.png

[mark mcfarlane]

My experience is wood 1/4" thick will air dry very quickly, perhaps even in a week or so depending on the species and what it is finished with, if anything. One way to check is carefully weigh the board. Then weigh it again after some time, maybe a week for something this thin, repeating if the weight has changed at all. When the wood has quit losing weight it is at equilibrium with the environment.

JKJ

Thanks John.