When is it OK to use PT lumber?

A friend asked me to make him a sliding barn door for his shed, and he wants it to match the 1x8 PT on the barn now. I was able to find enough decent 1x8 x 8' PT at a Home Depot, but as usual they are very wet. I've had it stickered in my garage for a week now, and my moisture meter still pegs at 55% on a few pieces, but a few are down to around 20%. This will be a standard barn door, just a simple "Z" of wood stiffeners across the back to hold the shape, no edge treatments. I was gonna leave about 1/4" between each piece to match the shed siding. The wettest pieces are about 7-5/8" wide, but the driest ones are a little less than 7-3/8" wide.

So, my concern is if I build the door now (using screws), will the additional wood shrinkage cause the wetter pieces to split down the middle as they dry out?

I would not use it. No telling what it will do, it’s like watching clowns , the old time really wacky ones . I would use a lot of plywood
and cover it with glued on canvas , then paint . A Proven method used on porches, boats ,sheds , and a lot of other stuff.

Thanks, but plywood is not an option. I'm just wondering if I should wait longer for it to dry, or will it be OK the way it is.

You really need the wood to be down to at least air dried before building a door with it that's nailed together. In my area that's about 12%. I'd want it even lower if using true joinery. You'll likely need to wait several months for it to get that dry. My experience with PT is that it almost always bows, twists, cups, etc when it dries unless it's nailed down. What you have may be unusable by the time it's dry enough to use. All things considered, I'd return the PT and look for something else. Air dried white pine, cedar, hemlock, Douglas fir, even cottonwood, all would be good choices.

John

If it really needs to be PT, you might want to see if you can get KDAT (kiln dried after treatment) lumber in your area. It starts out at <20% from the mill. I'd still sticker and weight it for as long as you can.

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Originally Posted by Ken Flesher

will the additional wood shrinkage cause the wetter pieces to split down the middle as they dry out?

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From my experience only a few out of many will split down the middle. Cupping, warping, and end checks will happen for sure. If you can let the boards dry you will know which ones not to use and have a better end result. I have made lots of barn doors, basement doors and screen doors from P.T. I use the 5/4 premium decking. I select the very best boards, looking for no pith, no big knots and quarter or rift grain. It is a tedious search. Dry them in a homemade kiln or attic. Another option is to use a better grade of kiln dried lumber and treat it yourself with copper green wood preservative. This is a stinky and tedious undertaking but it works. I treat tongue and grove car siding and use it to make old fashioned cellar doors. Several around town are going on 30 years and holding up nicely. If I ever get back to MO I will take some pictures...

I keep a good sized Stache of it drying all the time. Any time I walk through a building supply and see clear boards with no wild grain on top of any of the treated stacks, they go home with me. I like to keep them in a shed at least a year. I don't sticker them, but stand them straight up with air circulation around them. The ones that want to move will, and the ones that stay straight will stay straight. I end up cutting shorter parts out of the ones that move.

Here is one such dry 2x12. The cupola was made completely out of dry treated wood cut from short crooked, but dry pieces, including the sash. Even when I was building new houses, if a porch was getting a treated porch floor, the wood dried for 6 to 9 months before being fastened down. Often it was just left laying in place with no fasteners. Dry treated wood holds paint fine, but not dry not so good. Steps into 1828 museum house.

No KDAT around here.

Guessing that you may decide 'damn the torpedoes, full steam ahead' ;

The wood will dry at a reckless rate once hung up in the sunshine. Expect movement, end checks, surface checks, warp, twist and bow, but probably no boards will split thru.

1/4" gap to match the existing siding? Does snow blow thru into the shed, and bees?

"A simple Z across the back"; the horizontal stiffeners could hold the assembly kinda straight while it dries. Make sure those are the best pieces you have and put them on the inside and outside.

Screws may let you replace any really troublesome boards next year.

I would store longer if no other wood is an option. Get some air movement and maybe dehumidification going in the garage. Watch the cup when putting it together Maybe seal the endgrain before it hits the sun.

There is a critter called KDAT - Kiln-Dried After Treating.

The wood goes through the normal pressure treating cycle, and then dried in a kiln, same as newly sawn lumber

It is not as widely available as normal PT. You'll need to check specialty builder's yards. Be aware - after treating-restack and sticker - kiln dry - restack and desticker. All are cost items that show up in the higher sales price.

But, IMO, it is well worth it. You know what the dimensions are and will be.