Question regarding humidity affecting wood

[Aaron Broomhead]

My question is to anyone living in a humid area. I am going to be starting a project soon for a friend who lives in Florida. I live in Utah and am concerned about a project going from a dry area like Utah to a humid area like Florida. I quite possibly am over analyzing this and it may not be as big an issue as I think it might be. I have never had to deal with high levels of humidity so this is very new to me.

Any suggestions on construction, type of glue etc. Really any suggestions or information would be helpful.

[Carl Beckett]

My experience is, that yes its an issue to consider. (have done a number of pieces that go from high humidity areas to low humidity areas)

Things like gaps, drawer slides (if you make your own), clearances, panel movement, and even panel or top flatness are all affected.

The only thing I know to do is to consider the fact that wood moves when you are building it. Dont just glue and screw things down. Make sure the gaps around the drawers are consistent and the drawers work smooth (and since you are going to higher humidity, maybe make drawers or door gaps slightly larger than you would otherwise. Slightly)

Consider breadboard ends if you have a top glueup (I dont think glue type will matter - good glue joints work well). Careful of attaching solid wood to plywood (if there is a bottom or inner structure) - especially across the grain, because the plywood wont move like the wood will.

Im sure there are other better recommendations here - give us an idea of the project and you will get some more specific recommendations of design detail to accommodate wood movement.

[Joe Angrisani]

Build "sloppy" and plan for the expansion between Utah and Florida. Drawer fronts and sides are going to get wider between Utah and Florida (perhaps 1/16"-3/32"), so make the openings bigger top-to-bottom. Solid wood door panels are going to get wider so give them plenty of room to grow inside their frames across the grain (not so much in the length). Breadboard ends should be slightly longer (in Utah) than the solid wood table top is wide. Stuff like that.

Remember... Wood expands and contracts across the grain. It's fairly stable with the grain, and quartersawn stock is more stable than flatsawn.

[Bill Davis]

" I quite possibly am over analyzing this and it may not be as big an issue as I think it might be."

Here's some help on 'over analyzing' it.

Find the average RH for your location. (Ideal situation would be to build the project with woods MC stabilized at avg 'equilibrium RH' in Fla)
Find the average RH for the Florida location. Also yearly RH swings. Indoor different than outdoor RH.
For the wood species you will use find the radial and tangential shrinking/swelling percent. (or pick a wood with low shrinkage values)
Know the MC of the wood you are working with. (moisture meter is oft forgotten but highly important shop tool)
Realize that kiln dried wood doesn't maintain that same, unknown MC. Wood's MC and therefore dimensions vary with ambient RH. Plan for it.
Select grain direction of the wood for parts of the project that might be problematic if expansion occurs. (radial shrinkage is 'about' half that of tangential.)
Select a finish that will minimize moisture adsorption/desorption. None will eliminate it - only slow it down.
Make wood joints with matches grain direction where possible.

It is worth considering the effects of moisture on wood in any project. It has been said that over 90% of all problems with wood are related to moisture so learn the effects of of the two and design/build with them in mind. Don't fight city hall - er I mean mother nature. Work with it wisely.

"In summary, learn to live with the dimensional properties of wood by following some guidelines.
First, season lumber to the average moisture it will have in use before working it.
Second, provide the finished work with the most impervious finish consistent with its intended use.
Third, Design the piece to allow normal dimensional change to take place. (Even if you don't think it necessary, it's a nice "failsafe.")
Finally, think about mechanical restraints and chemical stabilizers only when instability still remains unresolved."
Quote from R. Bruce Hoadley, Understanding Wood, pg 141 (A dynamite book, by the way.)

[Neil Brooks]

They're all -- as usual -- saying the right stuff.

Wallow out holes, where you screw -- example -- a table top to a cleat.

If you put T&G paneling in something, you can shoot a brad in the center of each panel, but don't glue the panels into a frame.

Ditto for a raised panel, or any panel/stile+rail door.

If you HAD the ability to get the wood to its EVENTUAL EMC BEFORE you built it, you'd pretty much solve the problem, but ... if you live in Utah ... why would you want to endure Florida humidity ;)

Good luck !

[John TenEyck]

You should read the sections in Bruce Hoadley's book that pertain to wood movement before you start this project. He not only talks about why wood moves but how to calculate how much it will move based on it's current MC and the humidity where it will be used. Following his calculations you will know, precisely, how much gap to leave around the drawer fronts or between doors, how to size floating panels, etc. With that knowledge you'll be able to design/build the project knowing you won't hear anything but praise from the owners. Good luck.

[Neil Brooks]

Since -- wisely -- it came up twice, lemme' just say that ... if anybody asked me to recommend the FIRST woodworking book they should read, I'm pretty sure I'd go with Hoadley's.

There's a saying in life, and ... I forgot it, and started banging boards together, when I first put up a shop:

You gotta' go through the steps, one by one, in pretty much anything you learn. If you SKIP a step, you'll inevitably wind up learning it the hard way.

Figuring out a few thing about this marvelous, magical, and COMPLICATED medium in which we all work ... was the step I skipped.

No disasters, but ... I'm vastly more comfortable doing what I'm doing now that I've spent some time with Hoadley :)

[Alan Schwabacher]

The chapter on water and wood in Hoadley is excellent. The same information is also available in the Forest Products Laboratory Wood Handbook. It does not read quite so easily as Hoadley, but it's free. Here's a link to the relevant chapter:
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr190/chapter_04.pdf

[Danny Hamsley]

In Georgia, the EMC inside my house in the summer (air conditioning) is right at 9.5 - 10%. That would probably be a pretty good number for a target for Florida if you can get the wood to that M% in Utah.