Insulation Foams Outside

Words: Steve SayersUrethane foams are also a two-part mixture, like urea-formaldehyde foams for concrete blocks, except they're very adhesive and they expand. Polymaster Foam, Knoxville, Tenn., markets both foams. The company reports that when urethane comes out of the gun, it goes on like thick paint but then "grows" very quickly and sets almost immediately.

The company explains that there are various densities of foam from half-pound foam — very fluffy and resilient — up to three- and four-pound foams that are used in roofing. The two-pound foam can be sprayed on the exterior of concrete blocks to a thickness of one inch. This provides an R-7 insulation value while creating a vapor barrier at the same time.

Standard building design calls for a wythe cavity, or air space between concrete blocks and the brick veneer of the structure. This space allows wind driven rain or condensation to escape the wall before it reaches the block. With conventional wall designs, it is always recommended that the block wall be damp-proofed as an added precaution. With sprayed on urethane foam however, the product insulates and waterproofs in one step.

In the Northeast, for example, where bad storms come ashore and sometimes water gets up where the wall meets the roof structure, when they spray the urethane on the outside, they spray the overlap as well, so nothing is going to get through.

PolyMaster describes two-pound foam as a 100 percent closed cell product that water simply will not penetrate. The company cautions that only foams two-pound and higher can be regarded as vapor barriers. The result is a wall that, as one observer commented, "looks like a cocoon." Or as another says, "They have added a couple of points to the R-value, they've got a one-step process to waterproof the wall, and when the building is finished being sprayed, it looks like a refrigerator — totally sealed."

A more common approach to insulation in the wythe cavity is the use of foam board, often referred to generically as "blue board." Sold under a variety of brand names, this product is generally one inch thick, yielding an R-5 rating. Hung in sheets or panels, there are gaps through which water can seep and heat can escape. As PolyMaster points out, you've got a much tighter structure with the urethane. And since masons are paid to lay brick and block, they generally hate hanging blue board. Just like with foamed-in-place insulation in the block cavities, masons build their building and walk away from it.

Incylthane 2000, the urethane foam that Polymaster markets, is a 2.0 lb/cu. ft. density, closed-cell foam. Trained applicators apply it as a spray to the masonry block wall, the foam reacts, expands and cures in-place, forming a seamless insulating and waterproofing membrane. Incylthane has a superior R-value, as well, yielding R-7 per inch of material, two points higher than "blue board."

The cost of urethane spray foam versus blue board will vary from place-to-place. "On average," Steve Sayers, president of PolyMaster claims, "urethane foam will cost about 25 cents more per square foot. On the other hand, that extra money buys you an easier to use and more thorough insulating product."

Insulation Foams Outside

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