Spray foam is a great tool for insulating and weatherizing. It can be applied to horizontal and vertical surfaces, can be the air barrier and vapor and thermal control layers once cured (at least for closed cell foam) and provides some of the highest R-values per inch available. It slices! It dices! It makes great sushi!
Well…it does have some drawbacks. The green benefits are hotly debated being a fossil fuel derived product. The tremendous utility comes at a price as well as all flavors of spray foam are costly relative to other insulations. Citing reactions to the product, some customers have filed a class action suit against the foam manufacturers. Lastly, the actual application of the product is tricky, subject to many factors.
Thermoset Polymers and You
Spray foam insulation is a thermoset polymer. For those of you without an advanced chemisty degree (or like me haven’t yet read Wikipedia), a thermoset polymer is a heat activated plastic polymer. It usually starts in a liquid or malleable solid form which through chemical curing assumes a solid form.
Spray foam insulation of the sort we’re discussing are two chemical components which when mixed rapidly heat up and cure into a solid form. This seemingly straightforward process can be problematic in real life application, particularly in the cold.
Spray Foam Shrinkage and Other Fun
The manufacturers of spray foam are a pretty meticulous bunch. The technical specs are pretty clear about proper temperature ranges and substrate conditions (that’d be the surface being sprayed). And most installers are top notch but there can be issues. Cold weather can play hell with foam applications, leading to the most common problems: shrinkage and poor adhesion to the substrate.
Spray foam is a two part polymer with the two components referred to as the ‘A’ and ‘B’ components. Improperly mixed foam is a common problem but one that could occur in any climate. We’re looking at challenges specific to a cold climate.
The surface onto which the foam is sprayed needs to be within the manufacturer’s specified range. An important note here is that we’re talking about the substrate surface temperature, not the ambient air temperature. Most spray foams spec a surface temperature range between 60 F and 80 F. An uninsulated wood sill on a very cold January day could easily get below 60 F. Hell, it would probably get below 45 F.
This problem can easily be sussed out with a simple laser thermometer, testing the actual temperature of the spray surface. When applied to an overly cold surface, the final foam cure can be gummy and shrink away from the edges.
Spray foam rigs are large temperature controlled trailers. The two part component tanks are stored in these trailers, sustaining an appropriate warm temp. The components have a spec’ed temperature range just like the application surface.
When one or both components are off temp, the mix can be off and affect the final foam set. The application may end up not adhering well or be ‘A’ rich (which ends up crunchy and fibrous) or ‘B’ rich (gummy and pliable). None of this is good.
Ice on Substrate
XPS foam board may be an option with modern formed concrete foundations. But older rubble or brick foundations would need to be spray foamed. Heavy moisture levels and freezing is an all too common occurrence with these foundations. If ice had formed on the spray surface and then were sprayed over, no connection would be made with the substrate. Once the ice melts, the foam could pull off the surface. Another not good.
Spray foam is one tool an insulator or auditor can use to address house problems. Just be aware of the effects that cold weather can have on it.