Several years ago my dad was talked into spray foaming the ceiling of the attic with spray foam. Ever since there has been a tremendous amount of dust and bad smell. Lots of health problems have also occurred. We had foam tested and it was offgassing. Company finally came in and removed most of the foam. Unfortunately the house was built in 1920’s and has tongue and groove under sheet rock. There is still a bad smell. Dust is not so bad. Health issues include severe burning of lips, pain in gums and teeth , throat, and eyes. Stomach problems are not as bad as before. Vents were added to roof. What else can we do? Also we put sheep wool insulation in attic ceiling thus covering whatever residue is left. Is that a bad idea to cover the foam? Appreciate any input.

  • you did not exactly "cover" the foam, you only obstructed it from view
    – jsotola
    Nov 22, 2020 at 23:48

3 Answers 3


Where isocyanate comes from

Epoxy has 2 toxic halves that react with each other. When they do, the result is so non-toxic it's used to line food and soda cans. They are reacting to form a very long-chain molecule, which is very strong and tough.

The 2 parts "hold hands" like this: A-B-A-B-A-B-A-B-(repeat a lot)-A-B-A. They don't have to be infinitely long, just long enough to entangle.

Formed-in-place polyurethane works the same way. You have a toxic "A" part and "B" part that react to form a non-toxic long-chain molecule that is very strong and tough. (you're not interested in those properties in foam, but I work a lot with polyurethane paints, and if water contacts it before it cures, it will foam up).

If properly mixed, the isocyanates will be 100% consumed. The only way that doesn't happen is if

  • The person used too much B-part, either by accident or on purpose because of a misunderstanding of how polyurethane works.
  • The person didn't blend/mix enough, and so inside the bucket are zones too rich in B-part.

If the stuff is turning to powder, that raises some serious questions about whether it was mixed properly. It might be worth obtaining a small amount of it and intentionally mixing it with too much "B" part and see if that makes it behave like yours. If so, I'd consider lawyering up and going after the installer for the health problems.

What isocyanate does

Read the MSDS and the CDC page, but isocyanate is an immune system irritant that can cause anything from "allergy to isocyanates" to some real immune system damage if you get a major slug of it.

However, as the CDC page discusses, isocyanate is very chemically aggressive so it is also very short-lived in the environment. It really wants to hook onto "A-parts" and will grab almost anything, including water vapor. So the isocyanates should have entirely reacted within a week or so. It's not a vapor itself, so it won't waft down.

But if you were exposed to a lot of it due to improper mixing, that might have done some damage.

But otherwise, any long-term health problems must be caused by other chemicals - the isocyanate is gone now.

What to do about it

Don't fall into the trap of "doing what is easy instead of what is effective". If you want to stop being sick, you need to do what it takes. You alone must decide what your health is worth.

So it sounds like somebody chiseled out the bulk of the foam material. But I presume a lot of it was in direct contact with the wood, and I gather the part touching the wood is still there.

Well, that's not good enough. You will need to encapsulate it.

  • First, remove all the material you can. I would use a wire-brush or whatever else works. Use a shop-vac that has a HEPA filter so you aren't spreading it around even more. Wear a dust mask yourself, preferably an N95 if you can obtain one during the pandemic.
  • Then, with dust removed and after a water wipe-down and letting that dry, seal the surfaces with a primer. Now my favorite primer is - ironically - a 2-part epoxy, but it is VERY fumey. My second go-to is KILZ Original, but that is also quite fumey, being an alkyd primer. So to minimize environmental sensitivity I'd use KILZ 2 preferably in a low-VOC form.
  • Prime all surfaces that ever had foam. I recommend 2 coats, and in any case use all the paint. Never keep old latex paint around - now with the low-VOC requirements it is very susceptible to mold and fungus - and if you think you have problems now, try stopping the foul stench of moldy paint!

You'd be working in the attic a lot. I gather it doesn't have floorboards. Take some plywood sheets up there (cut them down as needed to bring up there) and screw them down temporarily so you have a comfortable work area and aren't having to play Spider-man across the joists carrying tools and vacuums.


Spray Polyurethane Foam (SPF) insulation systems used formaldehyde and other volatile chemicals called "isocyanates" that "cured" the foam once it was sprayed. In theory, the curing chemicals were supposed to become inert after a period of time, often listed as 24-48 hours from initial installation. Over the years this has been suspected of being wrong, and there is "outgassing" taking place for years.

That said, if the foam was removed, the small amount remaining would be unlikely to have significant amounts of outgassing taking place in a ventilated attic. The foam itself, expanded polyurethane, is considered inert; you have polyurethane on a lot of furniture, hardwood flooring, wall paneling, etc. etc. The only potentially bad stuff was the stuff that made the polyurethane get foamy.

What kind of smell is it? Formaldehyde has a vaguely pickle-like smell, isocyanates have a fruity odor to them (when strong). If what you are smelling is more like ammonia or urine, you may have rats in your attic or inside of your walls.

  • Isocyanates are part and parcel of polyurethane. They are not the foaming agent, they are half of the polyurethane - the "B" part specifically (it works like epoxy). I work a lot with isocyanate based paint, which does not foam at all (unless water contacts it, then oh yeah). If the 2 parts are mixed properly, the isocyanate is entirely consumed in the chemical reaction known as "curing". If you're heavy-handed with the B-part, or mix inadequately, cure can finish with isocyanate left over, and then, you've got a problem. Nov 23, 2020 at 1:43
  • Well, off gassing was legally proven. The smell at first was an extremely sweet old urine smell. Now it smells like old stinky paint, and it is a strong strong smell. But the health issues are the same. Lips blister like a burn, gums swell, breathing issues, extremely salty taste in mouth. No mice or rats. I recognize that smell. And have professionally treated property for rats and mice anyway. The house has also tested high for acetates. One builder told me that was from the spray foam.
    – Vhy
    Nov 24, 2020 at 0:31

We had sprayfoam done at our house, but the contractor messed up 4 ways for the installation that warranted removal of all the foam.

  1. mixed open cell and closed cell
  2. sprayed too thick
  3. sprayed pure resin
  4. delaminating from the substrates

We had an expert do the testing.

Currently we removed the foam ourselves but there still is fishy smell that lingers in the air on hot days or when we have the windows closed for too long. We will try priming using killz original to see if it will block the smell that might’ve gotten in the studs and wood. We will look into an ERV or whole house air exhanger.

Contractor has refused to do anything. Licensing agency has blacklisted contractor, but another agency gave him new membership.

  • HI this site does not work like a forum,. we expect only answers in this section. Jun 23, 2023 at 3:45

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