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Old 07-25-2009, 09:56 PM   #16
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PT lumber and ground contact


Look on the tag on the end of your lumber and see if it is .40 retention. If it is, it can touch the ground. I'd personally advise digging down so it doesn't...It'll rot sooner regardless of being treated. .60 is for direct burial, .25 isn't good for your application. If there's no tag then call the yard you bought it from and ask what retention the material you bought is treated to.

Plastic would help, but plastic also holds water and allows condensation...So it isn't a cure.

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Old 07-25-2009, 10:07 PM   #17
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Great information. How far down is sufficient to protect the wood? What is the degree of separation that is required?
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Old 07-26-2009, 01:19 AM   #18
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That's a judgement call. I'd suggest a couple inches just to be safe.
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Old 07-26-2009, 04:11 AM   #19
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PT lumber and ground contact


About 19 years ago, I had a deck built that used 6 by 6 inch supports and back then they were allowed to be installed in the ground. About 4 years ago, I noticed the base of one of the supports had some of its paint flake off and it appeared wet. I got a screwdriver and press it into the wood and it went in easily about 1-1/2 inches. It was dryrotting. It was an accident waiting to happen. I imediantly called a contractor to have both supports replaced. Our city now requires that supports be mounted above ground level on a cement pillar with a galvanized steel bracket. If you have inground supports, check yearly for dryrot at the base of it.
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Old 08-21-2011, 08:54 AM   #20
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PT lumber and ground contact


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ACQ (and CCA back in the good old days) lumber's use is classified based on the retention it is treated to. ACQ and CCA, as well as ACZA, copper azole, and a lot of proprietary names like wolmanized and yellawood are water-based treatments covered under AWPA standard C22. The treatment is carried in water and is forced into the wood under high pressure. The .25/.40/.60 etc is the retention weight in pounds per cubic foot of wood. So, a .40 treated board has .40 pounds of treatment per cubic foot of wood, by volume.

.25 retention is above ground use only. .40 retention is ground contact. That means it can touch the ground like a landscape timber would, but doesn't necessarily make it a good product for burial. .60 is for direct burial. If you have a wood foundation, it has to be .60. There are higher retentions available by special order for use in submersed or very wet applications like dock piers.

There is a lot of discussion about whether it is good practice to bury .40 ACQ for deck posts, etc. Personally, I think it is bad practice.

When dealing with treated wood, there's a huge difference between a piece of wood that is used on the ground or above the ground and a piece of wood that is completely buried in the ground. If the wood cannot expel moisture that is absorbed through its end grain, it had better have one hell of a good treatment (high retention) through its entire thickness if it is going to last long at all. The wood DM found in the forest had the ability to "breathe" which prolonged its life. Plus, it was probably CCA, which makes it a heck of a lot better than ACQ in my opinion.

If you build a treated deck, I strongly suggest using KDAT (kiln dried after treatment) lumber for the decking and handrails at least. Moisture content of undried treated wood can exceed 40%...That's why it is so heavy. That's also why it shrinks and generally freaks out as it dries. KDAT lumber is dried to 19% or lower moisture content, making it much much much more predictable. It won't shrink much, and is less prone to twisting, cupping, and bending. Southern Yellow Pine is a squirelly species to begin with, and KDAT lumber is definately worth the small price increase. Box stores don't keep KDAT...Gotta go to a GOOD lumber yard that sells to builders and commercial construction in most cases.
You seem very knowledgeable about this subject and was hoping you're still around to answer a question. I am building a polebarn in a fairly wet area of bottom land. I was thinking about painting the post with the new bedliner that they have available. What do you think about this?
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Old 08-21-2011, 09:21 AM   #21
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PT lumber and ground contact


Mark, Termite hasn't been around much lately. The twins, you know.
However, you should start a new thread asking your question in Building and Construction section.
Interesting thought though, I wonder what responses you'll get?

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Old 08-21-2011, 09:29 AM   #22
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Mark, Termite hasn't been around much lately. The twins, you know.
However, you should start a new thread asking your question in Building and Construction section.
Interesting thought though, I wonder what responses you'll get?

DM
Will do. Thanks.

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