Posted by Sherman in Idaho [72.47.153.105] on Saturday, December 07, 2013 at 12:13:55 :
In Reply to: Pressure Treated Lumber? posted by CSCameron [174.26.77.215] on Saturday, December 07, 2013 at 11:01:45 :
There are several reasons I wouldn't do it. The lumber itself is usually a poor grade. At least here in the northwest, it call comes from one plant in western Washington. They start with #2 "hem-fir", which really means western hemlock. This is a weak softwood that rots easily. As long as the preservative coating, which only goes in 1/2" or so, is intact, it holds up okay, but for bed wood you'll need to cut grooves and drill holes, which will let the rot in. Because the lumber is a low #2 grade, you'll be dealing with warpage, knots, and pith. There seem to never be any particularly good pieces in the pile, so you can't even high-grade it.
You can paint the cut and drilled parts with preservative, but it will only penetrate a little way, and if you were going to rely on painted-on preservative, you could have started with good lumber and painted it all yourself.
The east coast people, of course, can just go down to their neighborhood sawmill and buy custom-cut white oak. Out west we don't have that luxury. If I was doing a bed here (N Idaho) I would get doug fir or tamarack (graded "D FIR-L" at the lumber yard), and probably not put preservative on it. The "inland empire" doug fir is almost a different species from what they grow on the coast, and it's easy to find good dense pieces. When I'm at the lumber yard, I always take a quick look and see if they have any especially good units that day, and often I can pull out some clears (at #2 prices) to put aside for future projects.
Good dense inland doug fir or tamarack/larch will hold up for many decades exposed to the weather so long as it can dry out (bridges, decks, etc). The issue with truck beds is leaves, needles, and trash accumulating in a truck left out in the weather, which makes compost out of the bed. Since you're going to the trouble of restoring the bed, you won't abuse it like that. Either doug fir or larch are tough enough to survive that kind of usage. I would just avoid "hem-fir" (hemlock or true fir), cedar, or redwood. A coating of preservative can't hurt, but it doesn't penetrate far and the stuff they sell nowadays is not very toxic and it leaches out over time.
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