I'd like your advice on wood expansion

[Dick Snyder]

I am making a cover from teak to cover the mantle on my fireplace. The current mantle is really ugly piece of blue stone. The teak will match a teak entertainment center I built a year ago. The mantle will be covered on all sides. The mantle is 74 1/2". This is in a vacation home in New Hampshire. It will be down to about 55 degrees in the winter and maybe 80 degrees and humid in the summer.

OK, that was the long slow windup. Here comes the pitch. How much room would you leave for expansion? The side pieces will match up to some trim where the chimney and the wall meet so I can't just make it as wide as I want.

Your advice would be greatly appreciated.

Dick Snyder

[alexy]

Not enough information. Look at

how to estimate

[Leon]

Relative no length expansion and or thickness expansion. The only expansion that you will notice will be in solid board widths. Leave yourself a bit of wiggle for the boards to expand and contract in width. On a 12" wide board I would suggest as much as 1/4" wiggle room. This may not be an issue if the width/edges of the board are not between two fixes surfaces. If one edge is not confined there should be no issue.

[Dick Snyder]

Thanks. The widest board will be 7" x 74 1/2". I was most worred about length but I do have room on width as long at I place the two end pieces, which will be at a 90 degree angle to the long boards, with screws in oversized holes so the long pieces can move.

[Larry Blanchard]

Movement along the length is almost non-existent. Your end pieces are "breadboard ends", lots of info out there on those. Depending on the finish, 1/4" per 12" may or may not be enough.

Dewaxed shellac or oil based polyurethane do the best job at slowing water vapor from moving in or out of the wood, but nothing will stop it.

[Doug Miller]

"Dick Snyder" wrote in news:t9SdnSE9WvUFIBTNnZ2dnUVZ [e-mail]:

On a 7-inch-wide board, you might see as much as 1/8" difference in width; thickness changes at about half the rate that width changes, so if the board is 3/4" thick, you'll need precision tools to measure the change in thickness. And the change in length is effectively zero.

[Swingman]

Every woodworker needs to keep a copy of the following in the shop:

you will read, not only is the species of importance when selecting woods based on their reaction to moisture/seasonal changes, but also the cut off the log (quarter sawn, flat sawn, etc).

As a general rule, and for most species, if you want to reduce expansion and contraction across your board's face, try to select quarter or rift sawn stock for those areas/components which may be subject to dimensional instability due to moisture/seasonal changes.

(NOTE: these tables come in extra handy when you are faced with veneering/laminating different species of wood)

[Dick Snyder]

Thanks Larry. I will just be using teak oil on this project so it matches the entertainment center I made.

I think the breadboard ends idea will work well. Of course this isn't exactly a breadboard with an end piece attached to the main breadboard. My breadboard will be two pieces of teak sandwiched over a piece of bluestone. The breadboard end will be just over 3" high and will have to be attached to the top and bottom boards of the sandwich with a tongue and groove. It will will allow me to hide the mechanical fasteners on the top and bottom of the boards that will hide the existing mantle. I can cut plugs so even the screw heads won't be seen easily. I suppose I could even make teak dowels but I think screw heads hidden by plugs should work well on this project.

[Larry Blanchard]

Thank you - excellent reference.

[Jim Weisgram]

Woodworkers may find this tool handy as well:

are iOS and Android versions for $4 as well as a free web version.

[JayPique]

Does that hold true for flat, quartered and rift sawn boards - or just flat/plainsawn? I haven't heard that before.

JP

[Doug Miller]

JayPique wrote in news: [e-mail]:

It depends on the species, of course -- 1/8" over 7" is an average estimate for plainsawn lumber. Quartersawn should be about half that much, and riftsawn in between.