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 it’s performance so when it’s not installed correctly, it can get expensive for the the client, contractor and the planet.
If you look only at spray foam as a commodity, you’re sadly mistaken. Comparing spray insulation to the board foam one buys at the big box store which is produced in a highly controlled factory, to exacting, repeatable standards and is tested for quality before it leaves the factory. Whereas spray foam is manufactured on the job site; so we’re banking on the person pulling the spray foam gun trigger knowing some foam chemistry and building science; 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 company 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. The job site had bit of everything in it: 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
Now that you’ve selected the right installer puling the trigger, know that spray foam can’t be installed too thick, or it ruins the foam. As a rule of thumb, most 2 pound or medium density spray foam should be installed no more than 2″ thick layers – often called a “pass” or “lift” – at one time. It should cool, then another layer or lift of 2″ can be added on top etc…
The chemical reaction of the two liquid components making spray foam is a very rapid, exothermic (heat producing) reaction and good foam has to be cooled quickly or it cracks and “chars”. If it’s too thick, the insulative properties of the spray foam means that it traps the reaction’s heat in the newly sprayed foam. In the video below (sorry I was a bit shell shocked and wasn’t talking properly unlike Mike Cerqua of CallRich Eco Services) you can see the foam’s defects without digging much:
This core taken from beneath the button pulled off in the video above shows the cellular structure o the cured foam. The foam was over 6″ thick in one pass, where the manufacturer recommends no more than 2″ in one pass. Signs that the foam is not good include colour. density and cell size/uniformity. Here the foam is beige in the middle of the core and smelly (see below). The elongated cells and cracks in the foam suggest the foam was applied too thick. It’s difficult to get an accurate foam density when the cell structure is so open because the water fills the voids on the sides, even still this sample didn’t meet the manufacturer’s specifications for density.
The colour change from the base (greenish) to the top which is more yellow/verging on toffee shows an inconsistency in the foam. The large fissures and cells, some over an inch long, 1/4″ in diameter mean the foam is out of the manufacturer’s specification for acceptable spray foam. Even after 2 weeks of curing, this spray foam plug smelled very strong when compared to the sample below.
This spray foam core sample had a uniform cell structure (small bubbles) and was consistent in colour throughout.
Clear the work area
Preparing the substrate is equally important. We want the spray foam to be applied in even coat(s) onto a solid, clean and uniform substrate that foam will stick to. Experienced sprayers who know the behavior of the product they are spraying well can repeatedly get the foam to cure in a nice even coat. Note to self, with each layer or “lift” of spray foam applied, the defects get amplified resulting in a bumpier finish.
A brilliant spray foam application, keep this sprayer’s name in your Rolodex and never let him/her go! Clean, even application of medium density spray foam. 10/10!
Blisters or voids happen for many reasons including electrical wires, plumbing pipes, framing creating “shadows” in the foam, poor access in a tight space or just spraying over a messy area.
Settle those wires! Get an electrician to tame the wires. Strap them down to the wood framing. Much like a flashlight spraying light in the dark night, wires, pipes and framing will cause “shadows” in the foam as it’s projected out the gun. These “shadows” cause defects in the spray foam that can cause blisters that connect the living space to the attic.
This is wasted foam, time and carelessness. The sprayer sprayed on bits of fiberglass bats, wires and clumped up 6 mil poly; it’s a mess and riddled with holes.
The red marker indicated places where we found air leakage passing through the newly installed spray foam. This is not good.
In the video below, we see an air leak in the transition between the attic floor where wires and wood framing made for a tight space to lay down the first coat of spray foam. For the record, the conditioned living space was being depressurised with a blower door while the following short videos were taken in the attic of a home being remediated for ice damming.
A good sprayer will also appreciate the fact that spray foam won’t stick to 6 mil polyethylene. So don’t expect a durable air seal if this is your air barrier system. In the video below, we see that the spray foam stick to the ink on the poly, but no the poly. See why polyethylene should not be a substrate for spray foam:
Letting it all go to pot
Finally, the pot lights. Some pot lights are encased in a metal box that’s IC (insulation contact) rated:
and others are not:
The difference between the two is that one may be spray foamed directly, the other may cause the pot light to overheat and shoudl 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.