Avoiding Problems, Images 7-14

To keep a continuous eye on foam quality, it's a good idea to cut samples of material from each day's work, marking them with the date, location, and a dimensional measurement.

Smaller test pieces of the cured material can then be "thermally shocked" in a refrigerator or freezer to test for shrinkage. Note the straight-edged cuts between the smaller segments of foam.

After being chilled, the test pieces show obvious distortion. The shrinkage visible in the top sample, which had been left in a freezer overnight, is more pronounced than that in the sample at bottom, which had been refrigerated.

The obvious "hourglassing" in this larger chunk of foam indicates that the center of the freshly applied material was allowed to grow too hot. Though it was apparently stable for months after application, the onset of cold weather caused the foam to shrink and break apart.

The closed-cell foam on the stone foundation wall at right has been extended a foot or so onto the interior concrete wall at rear to reduce conductive heat loss; the concrete wall was masked before spraying to provide a neat termination. Depending on soils, climate, and other factors, such below-grade applications are sometimes limited to the above-grade portion of the wall — or graduated in thickness, with a thinner layer below grade — to reduce the danger of freezing the footing.

The rainscreen wall system in this commercial project uses a layer of closed-cell foam and an outer layer of brick veneer, separated by an air space. The outer skin of the foam serves as the drainage plane, while its inner face — sprayed against fiberglass-reinforced gypsum board on steel studs — acts as a vapor barrier.

Depending on the R-value required, open-cell foam can be applied to a depth greater than the framing before being trimmed back flush.

Denser closed-cell foam is much more difficult to trim. By allowing the foam to extend beyond the plane of the framing, this installer has created a major headache for the drywall crew. The author's tool of choice for trimming limited areas of closed-cell foam is an angle grinder fitted with a coarse 6-inch steel cup brush.

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