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.
No matter what happens someone will find a way to take it too seriously.
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.
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.
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
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.
I have never seen any pressure treated lumber with grooves or any other
identifying marks cut into the wood.
Are you sure you aren't talking about the shallow scalloping that occurs,
from the planer blades, when rough lumber is sent through a planer too fast?
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
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.
Chris Lewis, Una confibula non set est
It's not just anyone who gets a Starship Cruiser class named after them.
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.
This is Turtle.
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.
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