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Old 11-12-2010, 04:15 PM   #1
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PT Wood Shims on Stone Patio


O.K., pretty mundane question here but it's been bugging me a bit so I thought I'd see if I could bug someone else with it, if only for a minute.

Trying to stay on top of a outdoor kitchen being built on our existing stone patio and noticed that our contractor shimmed some of the galvanized tracks that frame out the bottom of the island with pressure treated wood. I figure any tracks that are actually raised off the stone in this manner is probably a a good thing, but I had heard elsewhere that some type of composite board (Trex, etc.) should be used for such shims to avoid eventual rotting. Does anyone think this is true to the extent that I should try to swap out the PT shims before the granite countertops are added? The face of the island is already covered in cultured stone so I'm not sure how easy this would be but by the same token, I'd really like to avoid unneccesary issues down the road (even if it's 5 years from now).

Thanks in advance!

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Old 11-12-2010, 04:57 PM   #2
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PT Wood Shims on Stone Patio


Pressure treated wood comes in various grades. So far as I know, most PT wood uses alkaline quaternary copper (ACQ) treatment, however the amount of copper varies depending on whether you want above grade (low copper) or ground contact (highest copper) PT lumber. For your application, you almost certainly want the ground contact variety of PT, and you should check to make sure that is what they used, else it is subject to rot. I do not know the life expectancy of Trex or similar plastic/wood composite materials, so I don't know if they are better than ground contact rated PT lumber.

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Old 11-12-2010, 07:40 PM   #3
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PT Wood Shims on Stone Patio


Thanks, Daniel. I believe you're right - we're talking about ACQ-treated wood but I'm not sure what level. I'm trying to figure out if it makes sense to try to re-shim (if that's even possible) and what the down-side is to not doing so. I suppose the wood shims could rot over a period of years and gradually cause the island to get out of level, but hopefully if that happens we could simply re-shim at that point.

Does this even make sense or do you think I'm missing something more critical here?
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Old 11-12-2010, 08:20 PM   #4
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PT Wood Shims on Stone Patio


He should have shimmed it with stone or plastic shims.
Ron
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Old 11-13-2010, 06:10 PM   #5
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PT Wood Shims on Stone Patio


I agree with Ron. P.t. wood is treated against fungi and insect rot, not water. You can purchase it specifically water treated by special order. It's not waterproof: http://www.greenbuildingadvisor.com/...-building-code

Composite decking is worse as it's made with 60% wood, more or less (secret recipe), that will rot and mold. Main requirement for 6" air space under composite decking.... http://www.deckmagazine.com/article/80.html

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Old 11-13-2010, 08:40 PM   #6
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PT Wood Shims on Stone Patio


Quote:
Originally Posted by GBR in WA
I agree with Ron. P.t. wood is treated against fungi and insect rot, not water. You can purchase it specifically water treated by special order. It's not waterproof: http://www.greenbuildingadvisor.com/...-building-code

Composite decking is worse as it's made with 60% wood, more or less (secret recipe), that will rot and mold. Main requirement for 6" air space under composite decking.... http://www.deckmagazine.com/article/80.html

Gary
Acctually just against termites and other wood ingesting, not ants.
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Old 11-13-2010, 11:22 PM   #7
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PT Wood Shims on Stone Patio


Thanks, guys. Good reading, GBR - I appreciate it.

I think I'll try to at least get some plastic (or composite, with minimal wood content) shims to insert alongside the existing ones if that makes any sense. I have a feeling my first suggestion to replace the existing PT shims won't go over so well.
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Old 11-29-2010, 03:29 PM   #8
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PT Wood Shims on Stone Patio


Also, take a look at Timbersil...no need to worry about it rotting, and it is completely non-toxic.

-WG
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Old 11-29-2010, 05:07 PM   #9
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Are you concerned about the rot or the chemical interaction with the metal? I think, as Ron and GBR have mentioned, plastic shims would work better
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Old 11-30-2010, 12:38 PM   #10
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PT Wood Shims on Stone Patio


Primarily the eventual rot. I understood that the galvanization of the studs mitigated most of the potential issues from ACQ in the pressure-treated wood. I ended up just putting some composite wood shims (available in packs at our local big-box store) alongside the original PT ones for peace of mind.

Thanks again guys for all of your help!

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