What aspect of the substrate is particularly critical before applying fireproofing?

Before applying fireproofing, the cleanliness of the substrate is particularly critical because the effectiveness of the fireproofing material depends heavily on proper adhesion. A clean surface ensures that the fireproofing material can bond effectively to the substrate, which is essential for its performance in providing fire resistance. Contaminants such as dust, grease, oil, or previous coatings can inhibit adhesion, lead to improper coverage, and ultimately compromise the integrity of the fireproofing application.

While factors like temperature and humidity can also influence the application and curing of fireproofing materials, they do not have the same immediate impact on adhesion as cleanliness. Similarly, color of the substrate is not a determining factor for the effectiveness of fireproofing materials.