When spray foam goes bad, it’s hard not to feel a bit sick. Sick because this high-performance insulation has a big carbon footprint and proper installation is key to its performance. When it’s not installed correctly, it can get expensive for the client, the contractor, and the planet.
If you look at spray foam as just a commodity, you’re sadly mistaken. The rigid foam that you buy at the big box store is produced in a highly controlled factory setting to exacting, repeatable standards and is tested for quality before it leaves the factory. Spray foam, on the other hand, is manufactured on the job site, so we’re banking on the person pulling the application gun’s trigger to know some foam chemistry and building science. That’s a rare combination, made rarer still if we expect that person to lay a lot of foam down quickly, cleanly, and uniformly.
The first rule with spray foam is “hire the installer spraying the foam, not the foam manufacturer or the foam brand.” By this I mean, the installer’s brain is the most valuable asset in selecting who will do the job. All else is secondary.
I was reminded of this a few weeks back when I visited a job site with terribly applied spray foam. It had every problem you could imagine: fire hazards created by the spray foam, charred foam, air leakage through the newly installed spray foam and missing foam. All in a day’s work!
Laying it on too thick
To install spray foam too thick is to ruin it. As a rule of thumb, most 2-pound spray foam or medium-density spray foam should be installed in layers no more than 2 inches thick. Each “pass” or “lift” should be allowed to cool before another layer is added.
This foam was sprayed in too thick a layer.
When the two liquid components of spray foam come together, there is a very rapid exothermic (heat-producing) chemical reaction. Good foam has to be cooled quickly or it cracks and chars. If it’s too thick, the insulating properties of the spray foam trap the heat. In the video above, I’m talking with Mike Cerqua of CallRich Eco Services, our go-to expert spray foamer who was called in to clean up this job. As we discover, defects in the foam become obvious without digging very far.
In this core, the color changes from a greenish hue at the base to a more yellow, toffee color at the top. The foam is inconsistent, and it had a very strong odor even after curing for two weeks.
This spray foam core sample had a uniform cell structure (small bubbles) and was consistent in color throughout.
Preparing the substrate is equally important. We want the foam to be applied in even coat(s) on a solid, clean and uniform substrate the foam can stick to. Experienced sprayers who know the behavior of the product can repeatedly get the foam to cure in a nice even coat.
Note to self: With each layer of foam applied, defects get amplified, resulting in a bumpier finish.
Blisters or voids are caused by a number of things — including electrical wires, plumbing pipes, framing that creates shadows in the foam, poor access in a tight space, or just spraying over a messy area.
A good sprayer also will appreciate the fact that spray foam won’t stick to 6-mil polyethylene. So don’t expect a durable air seal if you are using polyethylene as your air barrier system.
Get an electrician to tame the wires by attaching them to the wood framing. Wires, pipes and framing will cause “shadows” in the foam as it’s projected out the gun, much like a flashlight will cause shadows in the dark. These shadows cause defects in the foam.
The difference between the two is that one may be spray-foamed directly, while spraying the other one may cause the pot light to overheat and should be considered a very serious fire hazard. Either way, if the pot light is installed through your air barrier, it’s going to leak air.
The moral of this tale: if you invest in spray foam, hire a good installer, And if the foam is part of the air barrier system, test it for air leakage.
Greg Labbé is an energy and building consultant in Toronto. This blog originally appeared at the website of his company BlueGreen Consulting Group.
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