# PT lumber and ground contact



## Just Bill (Dec 21, 2008)

Correct, there were at least two different grades of chemical(CCA-no longer available) treatment. One was good for ground contact, one was not, and the labels attached to each piece reflected that. The one not rated for ground contact, would however, last much longer than untreated wood.


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## Maintenance 6 (Feb 26, 2008)

This isn't new. Even back in the CCA days there were different grades of pressure treated lumber, depending on the amount of treatment that was injected. Only .40 treatment was supposed to be used for ground contact. .25 was for above grade use.


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## DangerMouse (Jul 17, 2008)

not new news, no, but you'd be surprised how many ppl get hits for it and have to tear out and redo projects like decks.... like my neighbor.... 
just thought it might be a good idea to reshare this bit of general info to save anyone else my neighbor's headache. Po)

DM


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## gma2rjc (Nov 21, 2008)

I'm thinking about putting a low deck (just a few inches off the ground) out in the back yard either this summer or the next. Since the CCA is no longer sold, what's available now and is there still one that's good to use below ground level?

If there is, would I use the same kind for any boards that are going to be about 6" or less off the ground?


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## DIY_JC (May 20, 2008)

DangerMouse said:


> NOT ALL TREATED WOOD IS FOR GROUND OR CONCRETE CONTACT!


Thanks for pointing this out. I didn't know... and if I didn't read forums so much, I would have made a potentially expensive mistake at some point in the future. I knew there were differences between what was allowed a few years ago and what is allowed today. However, I did not know there were further distinctions with what is available today as far as ground/cement contact. Is there a 'grading' chart of the differences available?


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## DangerMouse (Jul 17, 2008)

gma2rjc said:


> would I use the same kind for any boards that are going to be about 6" or less off the ground?


yup, code here says min. 6". i'm doing 12"...ummmmm..... because i can... lol

check local lumber yards, some still have the better stuff around.

when placing orders on the phone for deliveries, be sure they understand you need foundation grade, or you'll end up sending it back for the right stuff like i had to one time. they sent me the right posts, but the wrong stringers......

DM


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## Termite (Apr 13, 2008)

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.


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## Termite (Apr 13, 2008)

Here's everything you ever wanted to know about treated lumber. Page 10 has a treatment retention guide.

http://www.buildingproductsplus.com/pdf/Pressure_Treated300.pdf


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## Scuba_Dave (Jan 16, 2009)

I always put cement down
I never bury the posts in the ground
Just makes sense long term


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## AndrewF (Dec 29, 2008)

This thread has me wondering all about the 27 6x6 posts we put in the ground for my 40x68 pole barn. All the posts sit on a combination of gravel and cement in the bottom of the holes, and then have 2 80lb bags around them, then backfilled with more gravel and dirt.

I bought it as a kit from the local contractor lumberyard, so I imagine they sold me the higher grade rated for direct burial...I hope.


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## DangerMouse (Jul 17, 2008)

they have a rep to think about, i'm pretty sure you can be confident they sold you the right product.

DM


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## mkliethe (Jul 26, 2009)

*what is the definition of ground contact?*

I have a variation on the discussion and wonder of someone can help. I am building a deck for grandma and want to avoid the inspector police.

As it turns out, the bottom of my beam will rest on the ground after I adjust for the final deck height, the joist height and the beam height.

I have three possible solutions.
1. Dig under the beam to open up some space and fill it with rock or some other drainable material.
2. Father says to cover the beam with plastic to prevent ground contact
3. I purchased the Copper based solution to treat the cut ends of the pressure treated lumber. Can i use this product to treat my beam for ground contact?

Thanks for your assistance. They did not teach me this stuff in pharmacy school.

mark


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## Scuba_Dave (Jan 16, 2009)

Where are you located? Frost line/snow?
What are you using for support posts/concrete into the ground?


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## mkliethe (Jul 26, 2009)

Short answer. Grandma is in East Lansing Michigan (go Blue). 
I have 42" deep holes with 25 inch diameter and 9 to 10 inch deep pads per the darn specs I received from East Lansing code enforcement dept. Posts will end up being right at ground level which allows (causes?) the bottom of the beams to be at ground level.

the posts are 6x6 inch ground treated lumber. 

hope this helps.


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## Termite (Apr 13, 2008)

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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## mkliethe (Jul 26, 2009)

Great information. How far down is sufficient to protect the wood? What is the degree of separation that is required?


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## Termite (Apr 13, 2008)

That's a judgement call. I'd suggest a couple inches just to be safe.


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## rjordan392 (Apr 28, 2005)

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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## markcrain (Aug 21, 2011)

Termite said:


> 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.
> 
> ...


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?
Mark


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## DangerMouse (Jul 17, 2008)

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


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## markcrain (Aug 21, 2011)

DangerMouse said:


> 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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