Last week we started to discuss some of the key components of SPF application in SPF Application, Part I and today we will continue that discussion.
Thickness is a critical factor in every application of spray foam insulation because the thickness has an impact on the insulation’s physical properties, including R-value, air barrier performance and vapor permeance qualities. However, possibly even more important for the SPF contractor and applicator, the applied thickness of spray foam insulation will have a direct effect on the quality of the finished product.
All SPF materials are created by a series of timed chemical reactions, some of which create heat and others that are temperature dependent. You probably understand that as more liquid material is applied in a single-pass, the final thickness will be greater. There is also another correlation, the more liquid material applied in a single pass results in more heat being created by the reacting materials.
Thickness per Pass
In the case of open-cell foam, most of the time there is not a maximum thickness per pass; because they are water-blown the excess heat is released by the creation of steam in the blowing reaction and the heat will not damage the physical properties of the open-cell foam. They can typically be sprayed as thick as desired, in a single pass, but be careful not to blow the rising foam off the wall. While it is not often necessary, given most applications, an average applicator can typically spray 6” to 8” in a single pass and I have seen skilled applicators spray 10”+ in a single pass. On the other hand, open-cell foam generally has a minimum thickness per pass, typically around 2” to 4” minimum, depending on the specific open-cell formula. It stands to reason, that if the amount of heat created by the chemical reaction is affected by the amount of liquid material applied, then if there is not enough liquid material, there may not be enough heat to complete the reactions and fully evolve the open-cell foam application, resulting in poor quality foam.
When it comes to closed-cell foam, thickness limitations are driven by internal heat generation as well. Maximum thicknesses per pass are generally 2” to 4” and minimum thicknesses per pass are generally ¾” to 1”. If too much closed-cell foam is sprayed per pass, the internal temperatures could increase significantly, resulting in poor quality foam and possibly fire hazard (combustion of the foam caused by excessively high temperatures). To apply greater thicknesses in an application, allow the previous pass to cool down before subsequent passes are applied. While, the surface temperature may be near ambient, the inside temperature of the foam mass could remain much higher and it is advisable to use a thermometer to check the internal temperature before applying an additional pass.
Application temperature and applied thickness can impact the effective yield of a spray foam product. Make sure to refer to the manufacturer’s guidelines for their specific minimum and maximum thicknesses per pass and recommended cool down time between passes.
Join us next week as we continue to discuss SPF Application, Part III
Subscribe here to get your FREE copy of 25 Spray Foam Insulation Frequently Asked Questions from Spray Foam Advisor.
