Justin Fink’s Canned Spray Foam Tip
Have a spray bottle handy, so you can mist the area with water before using the spray foam
I've been paying attention to energy-efficiency and air-sealing tips for many years, but I still learn something new every week. This week, I learned a very useful tip from my fellow Fine Homebuilding editor, Justin Fink.
Justin wrote a great article on canned spray foam, “You Don't Know Foam,” that appeared in the current issue of Fine Homebuilding.
I've known for years that one-component spray foam (unlike two-component spray foam) is moisture-cured. I've also known that freshly installed foam pulls moisture from the air to cure, and that builders working in very dry climates (like Nevada, New Mexico, and Arizona) know that it helps to mist a little water on surfaces before using one-component canned spray foam.
I didn't realize, however, that misting water before using canned spray foam can make a significant difference in New England. Nor did I realize that misting water can double the yield from a can of spray foam.
Quotes from Justin’s article
Here is what Justin wrote:
“Polyurethane cures by reacting with the moisture in the air. If very little or no moisture is available, the light and fluffy foam will collapse into itself as it cures. A light spray of water applied to surfaces before filling voids with foam will go a long way toward getting foam to cure properly.
“This is especially important when working in areas of low humidity, but it’s also best practice when filling deep voids. In the case of deep voids, apply the foam in layers, misting lightly between them. It only takes an ounce of water to cure an entire can of polyurethane foam, so think in terms of a spray bottle, not a garden hose.
“Manufacturers of some cans of foam, both straw-dispensed and gun-dispensed, recommend misting water either into the cavity to be foamed or onto the uncured foam itself. Polyurethane is a moisture-curing resin, and the water is said to help speed up the curing process.
“I was interested to see if a light mist of water sprayed into the footing tubes before applying each layer of foam would help the foam to cure more fully and thereby eliminate the uncured pockets from the first experiment. Indeed, just two spritzes from a spray bottle before each layer of foam yielded foam that was firmer, that cured in minutes rather than hours, that expanded to roughly twice the yield of the cans in the first test, and that left hardly any voids.”
Justin's full article, “You Don't Know Foam,” is available on the Green Building Advisor web site as well as the Fine Homebuilding website.
Subscribers to the Fine Homebuilding website can read the article by clicking here.
Subscribers to the GBAGreenBuildingAdvisor.com website can read the article by clicking here.
Martin Holladay’s previous blog: “Twenty Below and Off the Grid.”
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