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Crawl space joist painting…everything online is remidation, nothing is prevention?

Ryan_SLC | Posted in General Questions on

Hey all,

We have a new 100sq ft addition that is over it’s own crawl space with on wall being the house foundation that is a basement. No connection between the two. I’ve sealed off the venting and have poly on the floor. Walls have 2″ pink rigid foam.

I must be thinking something wrong. I want to do as iron tight as possible on the job. It seems mold prevention on the joists just makes good sense on this tiny area. Time and money being of no consequence.

I know the poly on the ground stops moisture coming up from the ground. Therefore, encapsaluated, I really have no issue with moisture rotting or molding the exposed joists…but why not add prevention through paint?

Through googling, the only thing that pops up about painting crawl space joists is about hiding or mold abatement. Nothing is on prevention.

Any insight on how wrong I’m thinking it that google can’t even find one example of this idea for prevention but it is a technique for remediation?

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  1. Expert Member
    BILL WICHERS | | #1

    As long as you keep moisture levels down, you won't have mold problems. If you do a good job sealing and insulating the crawlspace, and also make sure it can "communicate" with the rest of the structure (a fancy way to say that there needs to be some air movement between the now-encapsulated crawlspace and the living spaces), then you shouldn't have an issue with mold.

    If you want to put some preventative mold proofing on the wood, Zinsser makes a mold killing primer that works pretty well. I have usually used that primer as a preventative in areas where I've cleaned off mold, to help ensure the mold doesn't come back in the future, but it would work to prevent mold from growing in the first place too.


  2. Expert Member


    You won't find advice on protecting any new structural elements inside a building enclosure with paint because we aim to maintain conditions where moisture damage does not occur. A crawlspace that relies on coatings is build incorrectly and need remediating.

    Moisture problems come from two sources: Direct contact with wet materials, or contact with humid air. Both those threats are dealt with by following building codes. Wood is required to be separated from other materials like concrete by capillary breaks. An un-vented crawlspace has to be protected by vapour-barriers, and low humidity maintained by mechanical ventilation, connection with the continued spaces above, or de-humidification.

  3. Ryan_SLC | | #3

    So, honestly, if everything is sealed up right and good, it's not even a "belt and suspenders" idea?

    I can see why no one would want to do it, just was disappointed EVERYTHING online is an inspector asking why they see paint as a bad thing. Seems like an extra effort from an A+ student

    1. Expert Member
      MALCOLM TAYLOR | | #4


      Please take this in the spirit in which it is intended: What often distinguishes the work of DIYers when you tour their projects is the time spent on inconsequential things that really don't affect the longevity or quality of the build. That's fine if the important things are also done correctly.

      I don't think anyone would look at your addition and call it A+ work. At every stage you have had to make compromises, and do remedial work. Off the top of my head: You don't have a full rain-screen behind your siding. Your flashing has ended up as multiple layers. Your damp-proofing needs covering above grade. Your interior vapour-barrier is a patchwork of poly and tape. Your exterior trim may or may not meet your soffits. You don't appear to have a strategy to limit humidity in your enclosed crawlspace.

      None of these are insurmountable, but all were avoidable - and many seem to stem from you wandering off in odd directions, or completing a job without thinking through the next stage.

      A pretty good rule of thumb is if you don't see something being done, there is probably a good reason for that. The safest path for a novice builder (and it's one I follow too) is to replicate successful assemblies and sequences of construction. The result is both predictable and a lot less problem filled.

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