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Community and Q&A

Mold/Mildew and Painter’s Putty

craigcarter | Posted in GBA Pro Help on


I project manage for a remodeler that has been told by the client that each of the exterior remodels that have been done where post/columns and beams have been wrapped, prepped and painted the location of the nails where they have been filled with painter’s putty are showing dots of mold/mildew. See attached photos.


This is a large gated community where there are 3 – 5 different contractors work regularly and the client has record of who did which remodel and only those performed with this remodeler have been noted with the issue. There have been double digit remodels so this appears to be a large issue that has been brought to our attention more of a concern than anything. Additionally, it has been the same painter over the years for this remodeler.

The client said they were told we must not be using galvanized finish nails but common finishing nails…the shiny ones we were told which have been known to attract a fungus. Passing along what I’ve been told.

I am leaning towards the Painter’s Putty as we can scrape off the mold/mildew at the spot of each nail penetration that was filled and getting down toward the nail it is clean. The mold/mildew is just on the surface but only at the filled nail hole.

Has anyone experience this previously.

Here is what I’ve been told the steps the painter has been doing once the trim has been installed.

Treated post
Typical LVL or 2x for beams
All framing wrapped in PVC (brand not known likely Azek) and fastened using galvanized trim nails by nail gun
Painter fills nail holes with Crawford’s Painters Putty
Everything primed using an oil-based primer
Everything painted using latex paint

I’ve tried to call the tech department for Crawford’s Painters Putty – the brand the painter uses most. No answer and number disconnected.

I’ve called DAP to see about getting an answer too since they have a painters putty and they asked what was being filled and after I said nail holes they asked the material…which I replied PVC. To which they responded why would you use painters putty on PVC? I do think about product compatibility but never thought that painters putty is used for filling nail holes in wood only. By the way, the Crawford’s can said wood as well.

The DAP rep made a recommendation to use a vinyl spackle instead.

However, we still have the mold/mildew situation that based on the painters putty directions said to prime over using an oil-based primer and that is what the painter had done. So, why only the mold/mildew at the nail locations? Maybe the extended cure time of the painters putty is an issue? Or simply that the painters putty has organic properties that mold/mildew feed upon?

I decided to call Azek and they said some products can react with the PVC and they too only recommend a spackle for nail holes. Of course, I did learn that Azek has a filler crayon that fills nail holes and is completely compatible with their product…learn something new everyday.

Azek also said use either stainless fasteners or hot-dipped galvanized nails.

So, it sounds like there is product compatibility with PVC trim boards…

Painters Putty = NO
Galvanized Nails = NO
Priming PVC boards in oil = NO

Is this a case of using PVC with the painters putty, not using hot-dipped galvanized nails, putty not fully cured before painting, the oil primer on PVC (which Azek said no primer needed just acrylic latex paint) or a combination of all these things?

Of course, I now have been asked to write a standard for the trades…I think simply put follow product installation guidelines.

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  1. Expert Member
    BILL WICHERS | | #1

    Are you sure it's not RUST coming up from the bright nail? I've seen that happen before. Rust might look like "mold". If that's what's going on, galvanized or stainless nails should stop it.

    If you really have mold dots over each nail, the only thing I can think of is that the nail is doing something/enough to keep those spots ever so slightly cooler and thus a little more moist enough for the mold to grow there. That seems like a bit of a long shot to me, but it's all I can think of.

    You could try using a mold killing primer. Zinsser makes one that I've used before, and it seems to work OK. I've never used it for this nail/spackle problem though.

    I agree, following manufacturer's recommended installation instructions is a good idea.


  2. craigcarter | | #2

    Thanks Bill. I am going to go back and check with the carpenter's and see what nails they are using.

  3. Expert Member
    NICK KEENAN | | #3

    Crawford's Painter's Putty has a linseed oil base. In a humid climate linseed oil will mildew.

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