Fiberglass-backed polyiso got wet, now moldy on surface: to keep or not to keep? Remediation?
A few months ago I chatted back an forth with Mr. Martin Holladay about my project… I have progressed on it since then, but have ran into an unforeseen problem. Let me bring you up to speed:
I am building an apartment underneath a lean-to roof coming off of a post-frame shop building in climate 3. I purchased some used poly-iso foam boards to use as insulation on the underside of the existing metal roof. At this time I have reached this point (Layers shown from top to bottom):
Metal roof
2×4 purlins (with subsequent 1.5″ air gap)
radiant barrier foil (stapled to underside of purlins)
3″ fiberglass backed poly-iso board with joints filled with expanding foam and taped (tape didn’t stick well though)
2.5″ fiberglass backed poly-iso board with joints filled with expanding foam (didn’t bother with tape because it wasn’t working)
The next step is to install smart vapor retarder sheeting on the underside with taped seams (I have already purchased the materials).
Now here’s my issue: While it was sitting in a big stack awaiting application, some of my poly-iso at the bottom of the stack was exposed to some wind-driven rain and subsequently has some moldy patches on the backing. I discovered this while we were already in the middle of a big push to get the boards up and had a lot of volunteer laborers ready to go. We broomed off the fungi and continued installing it, thinking it will dry out and be okay, but it has since been eating at my brain wondering if that is indeed the case. This is only on the second layer mind you. The first layer was fine.
My question is, well,… how big of a problem is this? Is it possible to, I dunno,… sand off, scrape off, the mold and fiberglass backing that’s still visible on the underside of the exposed poly-iso sheets and go on down the road? Will it be a problem if we continue to put up the vapor retarder and ceiling finishes allergy-wise? Naturally the last thing I want to do is create a health hazard for myself or loved ones.
And when you answer, please put yourself in my shoes and answer with the understanding of the money and work hours that have already gone into the project – what I mean by that is, it’s easy for anyone to say “Just rip it out and start over!” But if it was your personal project and “just ripping it out” would involve losing $2500 in materials along with countless hours of labor, what would you do?
Many thanks!
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Replies
John,
I wouldn't worry about the mold -- but I would worry if the polyiso felt damp. You don't want to trap moisture between layers of rigid foam; ideally, the rigid foam would be dry when it is installed.
Moisture trapped between two layers of rigid foam isn't going to have much of an opportunity to dry out.
-- Martin Holladay
Thank you for your prompt reply Martin, and sorry for misspelling your last name on the first attempt.
The good news is that the rigid foam was indeed dry when we installed it. The bad(?) news is I can still see fungi of various colors on the underside of the panels. Not thick or growing mind you, but just... there. Like I said we brushed the panels off before installation, but there's still evidence of its existence.
Would you mind elaborating a bit as to why you wouldn't worry? My wife and I both suffer from mold allergies, myself more than her, and yet she is the one primarily concerned about this - It would help a great deal if I could give her a sound reason to not worry ;-)
John,
Most people aren't bothered by signs of mold on building materials, especially if the materials are dry (meaning that the mold is not growing) and encapsulated (usually behind drywall).
If you and your wife have mold allergies, I can't give you advice. It's time to talk to your doctor. I don't give medical advice.
Good luck.
-- Martin Holladay