Is there a maximum thickness that foam can be sprayed?

Yes. There are also differences in the maximum amount that can be sprayed between low density (half pound) and medium density (2pound) foams. Low density foams can be applied to the maximum thickness in one pass, but there are limitations to what those maximums are depending on the application. Please refer to the manufacturer’s specifications or ICC-ES Evaluation Report for detailed information. Medium density foams cannot be sprayed in more than 2″ passes (50mm) according to manufacturers’ specifications. Additionally, once 4″ has been installed, you have to wait 4 hours before the next 2″ pass can be applied. If spray foam is not properly installed, you may not receive the R-value that you have paid to have installed and the foam may not cure properly.