I have just had built a small (8x14) free standing storage shed. All of the exterior siding and trim is pressure treated. I am wondering just how good pressure treated wood is. I was told by the builders that since it was all pressure treated, I could leave the natural wood look or I could prime and paint it. I like the natural wood look and don't want to paint it. But I want to know if I should apply Thompson's Water Seal or similar or if it is okay just leaving the pressure treated lumber as is.
If you don't coat it eventually it will turn gray. I put up a fence last year with the new pressure treated wood (ACQ?) but did not apply anything and it still looks good, but looking at neighbor's old fences I know it won't be long before it starts to discolor.
My treated landscape timbers lasted about 15 years before they started to rot. They last longer than standard, untreated wood, but do not last forever. Use Thompsons.
Protective finishes do (at least) two things: stabilize moisture content of wood and block damaging uv radiation. Thompson's does little to none of either. Either a pigmented penetrating oil or paint would preserve the wood.
Since CCA-treated PT wood arrives saturated with moisture, you might want to hold off until the wood moisture-content stabilizes at reasonable level. If it's the green stuff.
Be aware that the older type of pressure treated wood, CCA, was available in at least 2 concentrations of preservative, .20, and .40. It should indicate this on the tag normally stapled to the end of the board. I think the .40 is good for direct burial in soil for up to 30 years, supposedly. The .20 is good above ground, but I have traditionally used the .40 for both posts and flooring on the decks I've built. Some pressure treated wood is available with Thompson water seal already impregnated into it. It is called Thompsonized by one company. I had a 25 X 40 deck at my previous house, and it required pressure washing every few years to get rid of the grey to renew it's look. I haven't tried any of the chemical deck washes out on the market now, nor any of the newer type treated wood, so I have no input on those.
Thats right, Pressure treated wood will not rot but it will still absorb water and can still warp under moist conditions. Sealing the wood will prevent this.
Sealing will also stabalize the color and look longer. And finally, sealing (especially paint) will seal in the preservatives which some people believe can be harmful to people and pets.
Thing I don't like about pressure treated (especially 2x4 and 4x4) is the little grooves cut in the surface to identify it as PT. this kind of ruins it for exposed work since you shouldn't sand this wood extensively. This would not be done to siding of course.
Depending on the manufacturer, depending on the size of the lumber, the mill will "slash" the face of the lumber so the PT will soak in better. It's not "identifying it as PT", but an aid to getting better soak of the preservative in shorter time. Manufacturing codes require that the preservative soaks in a given amount, and if the wood type/thickness doesn't allow it in a reasonable time, they slash the lumber to improve penetration.
Here, 6x6's and larger are always slashed. 4x4s sometimes. I don't remember ever seeing slashed 2x lumber - at least not PT suitable for decking or hand rails.
["High grade" PT rated for direct immersion might always be slashed even in 2x, but that tends to be the underside of docks, so who cares? ;-)]
Here, the slashes look like a series of 3/4-1" long, very narrow, slice marks aligned with the length of the board. Sort of like someone did a lot of stabbing at it with a very thin jack knife in a surprisingly regular pattern ;-)
Not at _all_ like planer scallop.
We use opaque stains for uprights, and transparent for horizontals. Only large posts (uprights) are slashed (if any). Given the relative thickness of opaque stains, and the fact that the posts seldom get much human contact, the slashes don't present a problem (either to the touch or in appearance). Indeed, the opaque stain tends to make the slashes disappear.
The decking, which is 2x material, isn't slashed, so it isn't an issue.
If you're stuck with slashed 2x PT lumber, look elsewhere, someone will have the unslashed type.
When you use treated wood , it is just treated wood to protect it to last longer than unpainted but does not bullet proof it for life. Treated wood is a good answer to making wood last longer in wet conditions but not the over all super dooper answer to protecting it without paint or other wood water treatments.
And Yes it will turn dim grey color in just a year or so. I would protect it in another way besides just the treatment from the manufactor.
The grooves are not to identify the wood as PT per se, but are cut into some species of wood to allow the treatment to penetrate sufficently. Southern yellow pine is very common for PT lumber because it is one of the species that does NOT require this "incising" or "slitting" to accept the pressure treatment.
Thanks. I had no idea what in the hell they were talking about. But being in the south, the only PT wood I've ever seen is SYP and you comment explains why I've never seen "grooves" in my lumber.
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