Recent EPA legislation has resulted in the introduction of new, low GWP (Global Warming Potential) blowing agents in gas-filled cellular plastic insulations – Closed Cell Spray Applied Polyurethane Foam (ccSPF) among them. This article will identify the formulation changes, strategic and application impacts, and considerations that applicator/contractors must be aware of in order to make an informed chemical system purchasing decision.
We all know in the spray foam industry, the chemical reaction between A-side and B-side produces heat and the heat of reaction causes the blowing agent to evaporate and become trapped in the cells of the foam plastic. Because we manufacture an insulation, the heat that builds up in the core of the foam takes time to cool. If the recommended single pass thickness is exceeded, the heat of reaction may result in scorched or thermally decomposed foam material. We’ve all seen that slightly brown layer through the core of a thick pass. That’s the reason manufacturers state a "maximum single pass thickness" (MSPT) in their application guides and technical data sheets. The maximum single pass thickness is formulation specific, and each applicator must be aware of the MSPT thickness. Remember, scorched foam is not acceptable and is more likely to produce a pungent odor.
With the introduction of Low GWP blowing agents, formulators went back to the drawing board and developed new formulations which are less likely to scorch when applied at single pass thicknesses greater than 2 inches. This was a response to contractors who have historically wanted "thick pass" foams – and "high Lift" foams were created. High Lift foams are formulation specific, and the technical and application guidelines vary from manufacturer to manufacturer. Read and understand the application and technical guides provided by the manufacturer for the specific formulation you are processing. Because we are applying ccSPF in thicker sections, they are more sensitive to the environment and the recommended MSPT may vary depending on ambient temperature and relative humidity.
As installers, you manufacture the foam on-site every time you pull the trigger and its important to understand the properties of these high-lift foams. From an exotherm standpoint, these formulations are more tolerant of thick passes and resistant to scorch at thicker single passes, which allows applicators to install greater R-values in a single pass and therefore increase productivity.
Let’s look at overall and core density. From top to bottom of a single pass, the density will vary. The contact surface (first ½ inch) will be a higher density than the core, and the top ¾ inch will also be slightly higher density foam than the core. In a two-inch single pass that variance is minimal, around 0.1 – 0.2 lb/ft3. With high-lift formulations, that variance can be more pronounced. The core density of a high lift formulation may be as low as 1.7 – 1.8 lb./ft3. At that density, the polymer structure may not be able to tolerate the stress of cooling resulting in cracking or the stress of cooling that large mass of foam may result in a loss of adhesion of the foam to the substrate. The stress of cooling is mass related (how much foam we apply) and the ability to withstand the force of cooling is density related.
Recent advances in formulations and application techniques now reflect a "two stage" approach to the application of high-lift foams. Many manufacturers now recommend a "2+2 inch" or a "2+3 inch" application. The application of the second pass is made after the first pass is allowed to cool to the specified temperature, whether surface or internal. This allows the installer to stay in position and apply the full thickness (R-value) of foam as required before relocating the scaffold or work platform – maintaining the productivity advantage of high-lift foams.
As manufacturers and installers become more familiar with low GWP blowing agents, contractors will become more familiar with the economic advantages these formulations provide. Read and understand the technical and installation guides from your system manufacturer. The SPFA also provides a TechTip on the subject TechTip 1-7 entitled "High-Lift Closed-Cell SPF Insulation" is available on-line to SPFA members.