Allowing for extreme humidity changes...

[David Rose]

I've about finished the "reading room" book shelves. See Terry! I can do something in less than 2 years. :D

The "reading room" is used about once a morning for taking a shower. No, it isn't out in the rain. It is a small room with a ventilator which runs during showers. Not rain, but forced water type. Oh, just ask Doc Zack. He will gladly elaborate. :D

The shelves are SPF. The tongue and groove boards for the back are 5" wide each. I allowed 1/8" clearance for expansion per board. Everything is cut. THEN I ran pine through the Wood Movement Calculator. Ugh! Going from 25% present shop humidity to 95% potential bath humidity shows a 5" board to move over a 1/4"!

I think I'm OK as the shower runs for only a few minutes a day and finish (probably flat varnish over shellac) should slow the movement way down. Also the ventilator should draw off much of the moisture. Did I goof?

Nothing is glued yet, but I'm ready.

David, who still needs to learn to "measure" *everything* twice before cutting

[Dr. Zack Jennings]

I don't know much 'bout humididity but it seems to me that that big old stack of magazines will block some of it. Did you ever git enough knee room figgered out on this deal?

I can't tell you how many sleepless nites I've spent worryin' 'bout yer condition, David. I hope everythin' works out fer ya....



<center> Sincerely Concerned in Arkansas
(signed)

[Steve Schoene]

What matters is really the AVERAGE humidity in the, dare we say it, bathroom. It may only reach 95% for less than an hour a day, but especially with your exhause fan, will average a lot less than that.

Shellac is about the best there is at slowing moisture vaper transfer. (Dewaxed shellac is better than shellac with wax--either mix your own, or buy SealCoat from Zinsser--SealCoat is the ONLY dewaxed shellac in a can.) With the shellac protected by varnish from liquid water the moisture transfer rate should be slowed significantly. The wood will still reach the AVERAGE moisture level of the bath, but shouldn't do major daily swings. Just be contentious in running the exhaust fan.

[David Rose]

Don't lose any sleep. They sell prune juice over here too.

And yeah, I found a decent way to get the leg room. I narrowed the shelves and extended the back a few inches. That gave me a "corner" to add short shelves kind of like a corner "whatnot" shelf in one unit with the shelves. The bottom "whatnot" shelf is above the knee. Make sense?

David

[David Rose]

But the calculator numbers blew me away. ;-) And I'm right at the point where I could still cut a couple of boards and regroove for the extra space without too much trouble. I decided to get more experienced opinions.

I'm mixing my shellac from flakes. I love the stuff generally.

Thanks!

David

[Jamie Buxton]

David, re the calculator numbers... Do you have any other woodwork in the room, like mitered casing around a door or window? What would be happening to those miters if the wood was expanding and contracting as much as you've calculated? The point is that the wood responds to the long-term average of the humidity. A short shower once a day makes the bathroom average somewhat higher than the rest of the house, but not by a great deal.

[David Rose]

Good point, Jamie! Thanks.