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Old 02-17-2009, 06:25 AM   #1
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PT lumber and ground contact


upon reading many threads where people are using PT lumber, wrong...i think some of the more knowing guys here should explain in simple english what the difference is between pressure treated and foundation grade for ground contact. i found a piece of the latter in the woods that has to have been there at least 20 years, and it looked like it was just left there the day before, after i dried the mud and cleaned it off. PT lumber would have been dust by then. NOT ALL TREATED WOOD IS FOR GROUND OR CONCRETE CONTACT! enjoy the thread, pro or con....

DM

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Old 02-17-2009, 07:02 AM   #2
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PT lumber and ground contact


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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Old 02-17-2009, 08:04 AM   #3
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PT lumber and ground contact


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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Old 02-17-2009, 08:19 AM   #4
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PT lumber and ground contact


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)

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Old 02-17-2009, 09:29 AM   #5
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PT lumber and ground contact


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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Old 02-17-2009, 09:55 AM   #6
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PT lumber and ground contact


Quote:
Originally Posted by DangerMouse View Post
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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Old 02-17-2009, 10:06 AM   #7
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PT lumber and ground contact


Quote:
Originally Posted by gma2rjc View Post
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......

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Old 02-17-2009, 12:03 PM   #8
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PT lumber and ground contact


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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Old 02-17-2009, 12:07 PM   #9
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PT lumber and ground contact


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

http://www.buildingproductsplus.com/...Treated300.pdf
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Old 02-17-2009, 05:34 PM   #10
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PT lumber and ground contact


I always put cement down
I never bury the posts in the ground
Just makes sense long term
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Old 02-18-2009, 10:40 AM   #11
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PT lumber and ground contact


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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Old 02-18-2009, 11:16 AM   #12
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PT lumber and ground contact


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

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Old 07-25-2009, 09:47 PM   #13
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PT lumber and 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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Old 07-25-2009, 09:49 PM   #14
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PT lumber and ground contact


Where are you located? Frost line/snow?
What are you using for support posts/concrete into the ground?
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Old 07-25-2009, 10:21 PM   #15
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PT lumber and ground contact


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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Last edited by mkliethe; 07-25-2009 at 10:25 PM. Reason: more info
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