I have several questions about the accursed wood movement problem due to changes in humidity.
If a board is completely finished on all sides with lacquer or polyurethane or whatever, how does moisture from the air penetrate into the wood?
How quickly does movement start on a thoroughly finished piece once the humidity level changes and how soon is it noticable? Will it start to swell up like a baseball player on steroids as soon as it goes from a dry shop to a muggy living room or does it take a while? And if so, how long before it becomes noticable?
How much of a humidity change does it take to really have an effect?
I understand that if you build something in Chicago in the summer and ship it to Arizona, bad things can happen to good wood. But what about staying within your own environment? Are the seasonal humidity variances in an adequatey heated and air conditioned shop, home, office, etc. enough to create problems?
Thanks in advance for your responses.
Replies
wooddood
To the best of my knowledge there is no finish that will stop all movement of moisture in the way you mean.
A finish can slow down the transfer of moisture, even to the point of the moisture popping the finish. (big bubbles in the latex house paint as an extreme example).
Some finishes are better at controlling moisture movement than others. You can find discussions on this subject in most of the woodworking/finishing message boards of hobbyist and commercial woodworker alike.
The amount of movement and time required for it to happen depends mostly on the difference in relative moisture content (difference between the air and the wood), but also on the ambient temperature and finish, type of wood etc.
As for how much of a change in humidity does it take to make a noticeable change? Here in the Coastal Washington State area from winter to summer (Wet to Dry) I've noticed as much as 1/16" change in Madrone per 12" . (finished or not!) Other woods are similar, some more some less.
An Oak dining table that my parents bought from a local high end furniture store was moved to Klamath Falls, Oregon, a high desert area (about 4000 ft and average precipitation of about 7" a year). The table is about a 4'x8' oval with a continuous 2 1/2" edgeband developed 3 - 3/8" to 5/8" cracks after about 2-3 years. After being moved back closer to the coast, the cracks have almost closed up again after 3 years.
As for potential problems, wood moves and you need to plan for it, engineer so that it can move without causing it to selfdestruct, allow greater clearance around solid wood doors, etc. if needed.
Wood movement pertains primarily to solid wood and mostly across the grain. Most plywoods etc. are more stable at least across the grain.
Some movement problems are due to wood that was not at an optimum moisture content to begin with (shrinkage).
Now that i've blabbed like a know-it-all, as long as your shop and the new enviornment are close you shouldn't have too many problems
To get a good idea of the potential for movement there is a good web site: http://www.woodbin.com/calcs/shrinkulator.htm where you can plug in various moisture levels (either as % of water in wood or as relative humidity in the air.)
While you won't see instantaneous change, several days or a week can certainly have a noticeable effect, depending on the wood, the finish, and how big the humidity difference is. Situation where moisture can become unbalanced, such as laying an unfinished board on a workbench when the board isn't at the equilibrium moisture for the humidity in the air can give you a warp overnight.
If you are talking about kitchen cabinets that will never leave the air conditioned room they are installed in, then you can probably ignore the rules for dealing with wood movement.
If the furniture is freestanding, and likely to outlast you, or be sold, then the piece should be designed for any and all climates because you will have no control over where it ends up.
It isn't that difficult to design furniture to accommodate for wood movement and doing so is one of the fundamental skills that separates hackers from cabinetmakers.
John White, Shop Manager, Fine Woodworking Magazine
John , can you point me to some articles and desing methods your magazine has had on the subject.
Thank you
Rich
You should remember the First and Second Rules of Woodworking:
1. All wood moves, period
2. All woodworkers disagree as the how much, reasons for, and repercussions and prevention of wood movement.
Seriously, there are so many variables that it easily surpasses applied science and gets in to preventative design and engineering.
Hoadley's book Understanding Wood has an excellent discussion of movement.
And the statement that Kitchen "cabinets in the same environment can ignore wood movement" - not likely. What happens in Winter when cousin Randy and his family come to help you paint the house? All that water based paint evaporating into the closed house, and since Randy insists on staying close by, he and his are showering once or twice a day, adding even more water. The first time I ever noticed wood move was in a kitchen while we were canning tomatoes - lots of heat and humidity, and all the cabinet door rails telegraphed beyond flush with the stiles. A couple of weeks later, they were flush again. That was 40 yrs ago, and those rails are still moving around a bit from season to season.
Dave S
No finish that I'm aware of is a complete vapor barrier, and that's what you would need to totally eliminate moisture changes. As has been previously stated, it will change the rate at which wood can pick up moisture but never eliminate it. The type of finish and the finish thickness will have a great influence on how fast the moisture can change.
There is no substitute for good design, don't ask me how I know this. Ok, I'll tell you. Back when I was a teenager and just starting out woodworking I made several projects from pictures in magazines, not really good pictures either. So I made a lot of errors in how the pieces actually went together. All of these pieces have cracked or split or self distructed in some way. Regardless of how they were finished.
The following is an excellent article on wood and wood movement:
http://www.woodmagazine.com/wood/story.jhtml?storyid=/templatedata/wood/story/data/250.xml&catref=wd22
There is also a chart of the water and watervapor resistance of various finishes.
last week i sent a message that was not replied to by anyone. perhaps i did not post correctly---any way my problem is that i moved to flagstaff az. from roseburg ore. i brought wit me a beautiful quilted and fiddle backed table that i built in or. my table has warped terribly--it is a slide leaf table the top and both ends have cupped. nay idaes from anyone about a cure or remedy for my lacquer finished on all sides table. jacj d
Jack,
How long ago did you move? If it is only a short time ago, then I would take the top off and store it vertically insuring that it gets air circulation all sides. If it doesn't flatten by the fall when the monsoon season is over and the air is drier then you could try stripping the lacquer and see if this will let the wood stabilize.
Doug
doug, thanks for your reply. i have put the table flat and placed bar clamps across the table upon some scraps of 3/4 wood. i then clamped the top to the bar, tightening until i pulled the table a little more than flat to the bar. i will leave this until the monsoon season is over and see what happens. will let you know the results---jack
Jack,
Unless this is caused by uneven finishing, which doesn't seem to be the case if I understand your post correctly, the problem is almost certainly being caused by a design that didn't take into consideration wood movement and/or choosing wood for the piece that wasn't appropriate for the design. If this is the case, then there is no simple solution, the piece would have to be disassembled and then rebuilt with the salvaged wood, if possible, but with the original flaws corrected.
If you could give a detailed description of the table's construction it shouldn't be too hard to figure out what went wrong. Clamping down the top will not solve the problem.
John White, Shop Manager, Fine Woodworking Magazine
"Wood will do what wood wants to do". I don't know who said that, but it is so true. My only advice is to work with it and don't fight it. You won't win.
I agree with John that no amount of clamping will change what is occurring with the table top. If equally sealing the top and the bottom or removing all of the finish doesn't cause the top to flatten then the problem is probably in the way the boards were grain-oriented when they were glued up. The only recourse at that point is to re-rip at the glue joints and re-orient based on matching end-grain direction.
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