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Wood movement question.

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Forum topic by FancyShoes posted 10-24-2015 03:34 AM 753 views 0 times favorited 12 replies Add to Favorites Watch
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FancyShoes

506 posts in 827 days


10-24-2015 03:34 AM

So we all have read and heard of wood movement, going from a 15% moisture to putting a project inside can cause wood movements.

A question I have been wondering about is; If you seal all sides of a project, do you still have to worry about moisture and wood movements?

I especially hear that with keeping stuff outdoors, and if you seal one side of a piece of wood, the other side will collect moisture and warp, so if you sealed both sides, would it move at all?


12 replies so far

View ElChe's profile

ElChe

630 posts in 799 days


#1 posted 10-24-2015 04:16 AM

You will literally get 10 different opinions from 10 different woodworkers. I think Bruce Hoadley is to blame following his publication of understanding wood. Before that woodworkers lived in ignorant bliss. ;) I have an antique desk from the early 1800s that was not finished inside and it is doing just fine. Same for a late 1800s harvest table. I think wood movement is over stated. If you use proper construction technique then it isn’t a problem. And if I understand Hoadley correctly, yes, wood moves regardless of sealing. But I confess 95% of the book is way over my head.

-- Tom - Measure twice cut once. Then measure again. Curse. Fudge.

View David Taylor's profile

David Taylor

326 posts in 550 days


#2 posted 10-24-2015 04:34 AM

Tom is right, and Bruce Hoadley is right. Yes, wood will migrate moisture into and out of itself even through a sealing finish. And, the wood will move, expand and contract. But as Tom says above, the amount of wood movement is overstated.

There are examples of incorrectly constructed pieces – a breadboard end fully glued along its length comes to mind – that may bind up a board that is trying to move, and something will have to give. Most often this will manifest as a crack. Finishing one side and leaving outdoors may in fact cause it to warp. How much, and the real question, does it matter? It may or may not depending on the piece.

My take has been construct the piece so it can move, and don’t worry from there.

-- Learn Relentlessly

View rwe2156's profile

rwe2156

2192 posts in 944 days


#3 posted 10-24-2015 10:08 AM

Yes, even with finished wood will move. Anyone will have stories of the tabletop finished on both sides that warped after sitting in a house or a couple months.

15% MC wood is not ready to build with, so you minimize problems with dryer wood BUT, regardless of MC, it is the balance of moisture on each side of a board that causes movement.

I think unbalanced moisture is the bane of all ww’ing projects. It took me a while to learn this and to just be patient with a project and factor in that the wood is going to have to sit around in stickers for a while.

Also, you never mill just one side of a board!

-- Everything is a prototype thats why its one of a kind!!

View FancyShoes's profile

FancyShoes

506 posts in 827 days


#4 posted 10-24-2015 11:32 AM

The whole milling one side of the board is a unique experience, I ran a board across my jointer to test out the jointer and set it aside, a while later I noticed it collected moisture from the one side, and I could see a color difference that it gave when looking at the end grain of the board, it was a half moon shape section of moisture that started on the side that was milled.

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Tennessee

2410 posts in 1977 days


#5 posted 10-24-2015 12:05 PM

Somewhere along the line, I read that even the best finishes, (normal stuff like lacquers and polys), only stop about 50% of moisture over the long run. So when you see an old piece that is not even coated inside, you know that they understood this concept and built accordingly.

And also, I have found that older wood, (longer off the log), even though it may show a 15% content one day, and an 8% the next, will not move as much as newer wood. Now I am talking ++years and decades off the log, not the difference between a plank one year off the log and a plank three years off the log. Something about the remaining sap finally crystallizing to help stop movement.

So even though you might seal all sides, it will still move, although it might move only about 50% as fast as uncoated wood.

-- Paul, Tennessee, http://www.tsunamiguitars.com

View Monte Pittman's profile

Monte Pittman

22005 posts in 1801 days


#6 posted 10-24-2015 12:44 PM

The worst wood movement I have seen is on pieces that travel between different humidity extremes. if the wood piece comes from a high humidity area to Arizona, it’s going to move a bunch. Most of the time it’s not an issue here.

-- Mother Nature created it, I just assemble it.

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TheWoodenOyster

1275 posts in 1398 days


#7 posted 10-24-2015 01:48 PM

I would expect a bunch of contradicting responses here, but I’m glad to say I agree with everyone above and they all seem to agree with each other. (Hooray! A first for us woodworkers!)

Sealing wood with any type of finish including lacquer and poly won’t stop wood movement, though it may slow it down a little bit. In general I would say that finishing one side and not the other would likely cause uneven moisture distribution to some extent, but it may not be large enough to care about. The important thing that others above have said is to take into account wood movement and plan for it. If you do, problems rarely arise. I have never had a wood movement issue and my shop is unconditioned. I live in North Texas where we do have some hot and humid days, though not to the extent that Houston or New Orleans or Miami have.

-- The Wood Is Your Oyster

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bearkatwood

1202 posts in 475 days


#8 posted 10-24-2015 02:07 PM

Some great answers!
Bridge makers have to worry about expansion and contraction of the metal in the bridge and they have to make allowances for it moving as well. That’s METAL, wood is an organic material and as such is going to move a lot more. The best way to work with instead of against seasonal movement of wood is in the construction of your piece and understand how wood moves, from the way you orientate your stretchers, how you glue it together (example given of breadboard ends) understand in which direction and by how much wood moves. It moves in all directions, but understand by what percentage each species moves in each direction. Some move much more than others. Try to build so that no matter how much the wood wants to swell or move it can without hurting your piece. As for sealing just one side of a piece, you are limiting that one sides ability to take in and expel moisture (not a problem if you planned for it). If your piece is going to be in an environment that is prone to wide swings in moisture and temperate, then you might want to think about sealing it all the way around. The same reason that some woods check and crack badly as they dry. Think about why we paint or wax the ends of a board after we mill it, to even the moisture equalization process. I think your best bet is just as I said before and consider the wood movement when you design and build your piece and it should work out fine. All the best and happy building.

-- Brian Noel

View lateralus819's profile

lateralus819

2236 posts in 1352 days


#9 posted 10-25-2015 01:31 AM

I made a top for an urn out of 2 pieces of maple and a piece of purpleheart.

I finished only one side of the lid. Needless to say it turned into a potato chip.

View FancyShoes's profile

FancyShoes

506 posts in 827 days


#10 posted 10-25-2015 03:08 AM



I made a top for an urn out of 2 pieces of maple and a piece of purpleheart.

I finished only one side of the lid. Needless to say it turned into a potato chip.

- lateralus819

Woah! We can make potato chips from storing peoples ashes in urns! That sounds awesome! More people should be cremated!

View AlaskaGuy's profile

AlaskaGuy

2406 posts in 1772 days


#11 posted 10-25-2015 07:26 AM

Plywood will move too.

-- Alaskan's for Global warming!

View a1Jim's profile

a1Jim

115202 posts in 3040 days


#12 posted 10-25-2015 02:21 PM

I always want to plan for a reasonable amount of wood movement in what I build. Like others have said 15% is too wet and sealng just one side is asking for trouble,you want to seal both sides of woods whether they are exposed or not ,just to equalize moisture content. Others have also said it depends on what your building,it’s construction,what type of wood you’re using,how it was cut(plain sawn or quarter sawn) and the intended use (indoor or out) as to what kind o problems you may o may not have with wood movement. Charles Neil compares wood to a piece of bread left on a counter top for a few minutes when you go to pick it up you notice the top has dried out but the bottom is still relatively moist. Wood does the same thing if left on a bench top without stickers even before we build causing cupping ,twisting bowing etc many times the defects are greatest the higher the moister content is that you start with.
If your building an outdoor bench nailing it together wood movement may have no consequence on your project but if your building a Bombe chest I think you better pay close attention to you wood’s moister content.joinry and where and how you construct you project

-- http://artisticwoodstudio.com Custom furniture

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