I am an air-sealing specialist, and I work with architects and contractors to help them make their buildings tighter. Air-sealing is a relatively new skill in the building world.
Currently, the most common go-to air-sealing material is canned, or gunned, foam. It’s fast and fun to use and it looks like it’s doing something. But it’s not the best product for air-sealing. The goal is not just visual evidence of air-sealing; the goal is comprehensive air-sealing that will last a long time.
Adhesion, flexibility, and durability are what we need in a good sealant material. Through years of testing and dissecting old foam seal work, I have found canned foam scores only “good” to “poor.” In terms of adhesion and elongation, canned foam and gunned foam do not perform as well as tapes or elastomeric compounds, caulk, and various sealants. The cellular structure of foam is full of potential holes. Probably worst of all, foam gives installers a false sense of “well done,” when in fact it is subject to poor installation.
As some readers may remember from my previous article (“Air-Sealing Without Foam,” May/13), I’ve been looking for an alternative to canned foam for a while. When I wrote that article, some tapes and caulks were the only available materials for creating an effective air seal—materials that would adhere well, stay flexible, and remain durable. But while tapes and caulks might perform better than canned foam, they can be labor intensive, costly, and slow.
Three years ago, I set out to find, or invent, an air sealant to match the speed of canned foam but with the reliable performance of other air sealants. My goal was to make a first-class air sealant suitable and affordable for any house in the U.S.
After years of messing around with different formulas and applicators, I came up with one system that will air-seal most leaks that come up in new or retrofit work. It is fast and nontoxic, works for all leak types, and emits no VOCs. It is a vapor-open (7.5 perms) rubberized latex (elastomeric) mixed with fibered granules that can be sprayed onto surfaces with a texture gun.
In this article, I’ll demonstrate how this new sealant works. On the particular job shown here, using entirely my formula, I’m air-sealing a classic 2,000-square-foot stucco ranch built in 1979 in climate zone 3.
Multiple Leakage Pathways
There are many ways air can leak in and out of a building. In this house, almost every switch and outlet box leaked air during a blower-door test, as did much of the baseboard and penetrations through the floor into the crawlspace. But the source of the greatest leakage was at the top and bottom plates.
The stucco was to remain, so we had limited access to seal the bottom-plate leaks at their source. Partial demo gave me insights into how the house leaked and ideas on how I might shut off the leaks. For example, along part of the exterior wall, we were able to slip a 16-gauge Simpson strap 7 inches behind the bottom plate shown in the photo above; it exited outdoors between the stucco and framing. This gap provided an easy path for air leakage. Elsewhere, a section of stucco was removed for a new door, revealing the exact pathway of this bottom plate leakage: air flowed behind the weep screed, between the building paper and the plate, and into the wall cavity.
In another area, I was able to slip a pruning saw under the bottom plate to reach the back of the stucco, which directly connected to the exterior. During a blower-door test, I held my hand 6 inches away from the outlet and the bottom plate and could feel air coming out.
The photos and captions in the two slideshows describe how I implemented what I put in the proposal, and what the owner agreed to pay for, to correct these and other leaks.
Delivery Machines
You can spray the elastomeric using a small hand-held hopper gun with an air hose attached. It delivers the material well, but the fluid will spill out of the hopper if it is tilted much more than 45 degrees. The hopper also has a limited volume capacity of less than two gallons.
I have used several full-size spray machines to deliver the elastomeric sealant. The Benron shown below (left) is a quiet workhorse. It is lightweight and portable (but requires a separate compressor), can handle a 100-foot garden hose, and can pump strongly until the cows come home. Benron is discontinuing this exact model but will soon come out with the Rotortex19- 245 Pro, available with or without a compressor. Davlin (davlincoatings.com) will be selling the Rotortex 245 setup the way it works best with my product. (Please note: I do not make money or commissions on what Davlin sells.)
The Graco RXT 1400 (below right; also available from Davlin) is light, noisy, and portable, and does a fine job. It is limited by its 25-foot hose but will fit through a 24-inch opening. Graco also makes the RTX 2000 (not shown), a heavier-duty rig that accepts a 50-foot hose.
Measurable Results
Successful air-sealing is first about access to the leaks, and second, about fastidious attention to detail. To ensure a successful job, you need to inform everyone on the crew what the goals are and how you are going to proceed, and you need to designate one person to be in charge and take responsibility of the entire air-sealing operation.
You get only one shot at air-sealing during retrofit or new work. After the stucco was originally installed on this house, access to the leaks was sealed up, and the leaks remained unaddressed for 38 years. We were able to significantly correct that, however. Before any work was done, we tested-in using a blower door with a whole-house air leakage of 11.2 ACH. The job tested-out near completion at 3.6 ACH.
The entire job took two people three days, and we used 24 gallons of elastomeric spray. Most of the work was in the attic, which took two guys one full day and 21 gallons of elastomeric. Because of the volume and throw of the material, we were able to cover potentially leaky areas in hard-to-reach places that typically never get fixed with other sealants. Actual spray seal time (covering the target) is very fast. What usually takes the most time in an attic is maneuvering around with the hose and gun. Another time factor is setup and cleanup.
