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Community and Q&A

Vapor Barrier for Wood Post in Concrete Patio

bigslothjim | Posted in Building Code Questions on

What is the proper way to protect the pt wood if the area in red is to be fixed with new concrete.  The column will be covered with a stone veneer.

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  1. GBA Editor
    Martin Holladay | | #1

    Is that a concrete patio? If so, the level of your concrete patio should never be above the bottom of your wood framing. You're asking for rot.

  2. bigslothjim | | #2

    it is a concrete patio. The wood is a column for a deck above that patio. The contractor cut the corner of the existing patio to accommodate the 6x6 post and column framing.

  3. Expert Member


    Martin is spot on. A very poor second-best solution is to cover the bottom of the post from the footing to 8" above the patio with a peel & stick waterproof membrane.

  4. Expert Member
    BILL WICHERS | | #4

    If you try to seal the sides of that post/column, you'll probably end up trapping water that will get in there either from the bottom or through the sides above the waterproofing. Water proofing goes both ways, do while it might keep water out in some areas, it might hold water in in others.

    Would it be possible to pour a small concrete pier on top of whatever that post is resting on to bring the masonry/wood interface up above the level of the patio at least an inch or two? If there is an existing concrete pier already there, you can drill in some anchors on top of it to pin the new concrete to the old. This way you keep the end of that woodend column up higher than the patio so that it won't ever potentially be sitting in water.

    Another option I've seen (but I don't really like), is to set a steel post into the lower masonry, then weld a flange on top of the steel post to support the wooden column. I don't really like this because it usually requires steel fabrication in the field, and the steel column can rust out in the same way that the wood clumn can rot away -- it just usually takes longer for the steel to fail compared to wood.


  5. bigslothjim | | #5

    What if they removed 3 sides of the pt wood and built around the 6x6 with cement block (the sides facing the existing patio)?

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