How does moisture content in the substrate affect fireproofing application?

• A. It can impair color matching
• B. It can enhance the coating properties when moisture is low
• C. It can weaken adhesion, hinder curing, cause washout, and lead to delamination
• D. It has no effect on performance

Answer: (C)

Moisture in the substrate directly affects how well a fireproofing coating bonds and cures. A damp surface prevents the coating from forming a solid interfacial bond, weakening adhesion. Water in the substrate also slows or stops the hydration and curing of cementitious binders, so the coating may not develop its intended strength and durability. If water is carried into the fresh coating, washout can occur, washing away fine material and leaving a weak, porous surface. Any trapped moisture behind the coating during curing can generate steam, causing blisters and potentially leading to delamination from the substrate. For these reasons, moisture content can weaken adhesion, hinder curing, cause washout, and lead to delamination. Color matching or the claim of no effect aren’t the primary concerns and don’t reflect these critical performance issues.