Since weather sealing Brooklyn brownstones is a large part of our business we are very into finding good products that seal all the cracks. The best solution on a practical level is Great Stuff Foam sealant by DOW Chemical.

We use a lot of it. We use it around windows, doors, and in pretty much any crack we think will let air pass between the outside and inside of the Brownstone.

This is a bittersweet thing because even though it does a great job it is still a very synthetic product made by a very large chemical company, two things our locally minded small ecological building company thinks is a problem for the earth’s environment.

So it is a trade off: great energy efficient weather sealing that lowers energy bills on the one hand and highly toxic chemicals by a multinational chemical producer on the other……

If you check the ingredients from the MSDS spec sheet it reads like a toxic nightmare. Here are the ingredient names and their percentage range of proportion:

Diphenylmethane Diisocyanate, isomers and homologues >= 15.0 – <= 40.0 % Polymethylenepolyphenyl polyisocyanate, polypropyleneglycol coopolymer >= 30.0 – <= 60.0 % Isocyanic acid, polymethylenepolyphenylene ester,p olymer with .alpha-1,2,3- propanetriyltris[.omega.-hydroxypoly >= 10.0 – <= 30.0 % Methyl ether >= 1.0 – <= 5.0 % Isobutane >= 5.0 – <= 10.0 % Propane >= 1.0 – <= 5.0 % Tris(1-chloro-2-propyl) phosphate >= 5.0 – <= 10.0 % Methylenediphenyl diisocyanate >= 10.0 – <= 30.0 % That's certainly not a shopping list for the health food store. I looks more like an ingredient list for agent orange. Methyl ether is nasty stuff. part of the paint thinner family your grandfather used while smoking a cigarette. Isobutane, propane, icocyanic acid....all great candidates for toxic pollution. Isn't Methylenediphenyl a meth amphetamine? Hell if I know. Some of the ingredients have given cancer to animals when exposed at high doses for long times. Which is not surprising. If you overload an animal with anything for long enough and it will cause a problem. Overload them with the above shopping list and you are pretty guaranteed it will cause problems for the poor fuzzy lab rat. The good news is that none of the ingredients are deemed harmful by California Proposition 65 (Safe Drinking Water and Toxic Enforcement Act of 1986). "This product contains no listed substances known to the State of California to cause cancer, birth defects or other reproductive harm, at levels which would require a warning under the statute." No birth deffects were caused by exposure to the product. Nor did the foam cause any harmful effects to marine life, according to the MSDS. The foam does have a pretty stable nature so it doesn't really mix with its surroundings, which is good. Long term, who knows. I suspect it does. Bottom line, we use the stuff. We know it is toxic. If we find something as amazingly effective that is healthier we will definitely switch.