Technical Abstract: Sodium bentonite (SB) gel and foam coatings were tested for their ability to suppress the rate of heat increase at the surface of commercial lap siding. Starch was added to some treatments to determine whether it stabilized the coating and prevented vertical slumping. A commercial fire protection gel coating was included in the study for comparison. Coatings containing starch and the SB gel sample had negligible slumping during burn tests while the commercial gel and the SB foam slumped severely during the test. In rheological tests, samples containing starch had higher G’, G”, and higher yield stress. The commercial gel had the lowest G’, G”, yield stress, and compressive stress. Surprisingly, the samples containing starch heated more slowly than samples without starch. This could be explained, in part, by the char residue that formed during the burn test that shielded the substrate surface from direct heat exposure. Drying tests were performed at 44°C to determine how long the coatings could remain hydrated under severe conditions. The SB gel coatings remained hydrated longer than the SB foam samples. Starch prolonged the drying time for both the SB foam and gel samples.