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Old 05-12-2012, 07:49 PM   #1
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Can PT lumber rot?


This pair of below-grade PT 4x4s say...YES!


This weekend's project. The posts were installed 15 years ago. Every once in a while, I see someone defend the practice of sinking deck posts below grade. You end up with a stronger post. You don't have to spend money on a connector. Great, but here's what you end up with eventually. No thanks.
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Old 05-12-2012, 08:37 PM   #2
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Can PT lumber rot?


A lot of things have changed since those old post were installed. There not even treated with the same stuff anymore.

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Old 05-12-2012, 08:52 PM   #3
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Can PT lumber rot?


Quote:
Originally Posted by joecaption View Post
A lot of things have changed since those old post were installed. There not even treated with the same stuff anymore.
Yeah. They've removed the arsenic, for health reasons. I'm not aware that the new stuff (ACQ or CAB) is more effective than the old stuff (CCA).
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Old 05-12-2012, 09:03 PM   #4
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Can PT lumber rot?


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Originally Posted by cortell View Post
Yeah. They've removed the arsenic, for health reasons. I'm not aware that the new stuff (ACQ or CAB) is more effective than the old stuff (CCA).
Yea the new PT is worse, I think you'll see more of this soon.
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Old 05-12-2012, 09:47 PM   #5
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Can PT lumber rot?


ANY lumber will rot when it comes in contact with the ground,that includes PT,i thought everyone knew that.
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Old 05-12-2012, 11:00 PM   #6
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Can PT lumber rot?


yes it will rot, it just depends on what you do to slow down the process. if you plan on putting the wood into the ground you have to change the type of treatment, marine grade has the greatest rot resistance. its used for warf applications
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Old 05-12-2012, 11:32 PM   #7
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Can PT lumber rot?


PT wood intended for ground contact is treated with more chemical than PT for above ground. However, it is impossible to get PT rated for ground contact at most big box stores and has to be special ordered most real lumberyards. So most PT posts are actually not properly rated for ground contact.
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Old 05-12-2012, 11:37 PM   #8
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Can PT lumber rot?


It's very simple. No one should bury pt posts in the ground. Another thing that is simple common sense.
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Old 05-13-2012, 02:57 AM   #9
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Can PT lumber rot?


To be honest I thik its impossible!
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Old 05-13-2012, 07:45 AM   #10
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Can PT lumber rot?


The highest levels of chemicals(CCA) for pressure treating 15 yrs ago guaranteed rot free, 40 yrs above ground, 20 yrs below grade. The usual grades available were not the highest. You had to look for the good stuff.
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Old 05-13-2012, 09:02 AM   #11
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Can PT lumber rot?


Quote:
Originally Posted by jogr View Post
PT wood intended for ground contact is treated with more chemical than PT for above ground. However, it is impossible to get PT rated for ground contact at most big box stores and has to be special ordered most real lumberyards. So most PT posts are actually not properly rated for ground contact.
Agreed…ACQ must have a chemical content of .40 pcf for ground contact and .15 pcf for above ground.

Most ACQ lumber easily available today has a chemical content of .06 pcf for 2X stock and .15 pcf for 4X, neither of which are suitable for ground contact.

Look at the tag stapled on the end of all treated lumber, it will show the pcf of chemical in the wood. If it’s less than .40 pcf then it’s not suitable for a fence post.
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Old 05-13-2012, 09:21 AM   #12
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Can PT lumber rot?


Quote:
Originally Posted by kwikfishron View Post
not suitable for a fence post.
Set them in concrete?
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Old 05-13-2012, 10:02 AM   #13
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Can PT lumber rot?


There are also different rating levels of PT.

A lot of the PT products on the market 15 years ago, were .25 PCF rated (rated for "above" ground water contact).

.40 & .60 PCF rating is the rating "for" ground water contact, and it is all we have been using since we educated ourselves on the difference.
Most Lumber Supply companies have routinely carried .40 & .60 rated PT.

Many of the Big Box stores only switched-over to it, about 3 years ago, from the lower rated PT.

Example:
Quote:
For waterborne preservatives, the following levels of preservative retention applies: 0.25 (lbs./ft³) – this is the minimum level for low exposure above ground contact elements; .40 – for ground contact elements such as fence posts and deck supports; and, 0.60 – for permanent ground burial such as wood foundations.
- http://www.schultzinspect.com/html/treated_lumber.html



(I see I missed that kwikfishron also covered this point)
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Old 05-13-2012, 10:36 AM   #14
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Can PT lumber rot?


what do you guys use for fence posts then ???
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Old 05-13-2012, 10:41 AM   #15
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Can PT lumber rot?


Thanks, everyone. This was very educational. My neighbor told me he had asked the builder during construction if those posts were rated for below ground, and the builder told him yes. Perhaps he was lied to.

That said, check out a tag I took from a PT 4x6 at Home Depot this morning. Apparently, a paltry .15 PCF is considered suitable for ground contact by HD. Wow.
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