Does Kilz Kill Mold?
QUICK ANSWER
No, Kilz does not kill mold. According to the manufacturer, Kilz Mold & Mildew Primer is designed to prevent NEW mold and mildew from growing on the primer film, but does not kill existing mold. Remove the mold first using detergent and water, then apply Kilz to prevent return.
Kilz Mold & Mildew Primer is one of the most popular products for dealing with mold-prone areas, and one of the most misunderstood. Despite its marketing, it does not kill existing mold. The product description from Kilz itself is specific about what the primer does and does not do. Here is what the manufacturer actually says and how to use the product correctly.
Does Kilz actually kill mold?
No. Kilz, made by Masterchem Industries, states that Kilz Mold & Mildew Primer "is designed to prevent mold and/or mildew from forming and contaminating the primer film before topcoat is applied." The key phrase is "prevent forming," not "kill existing." The EPA-registered active ingredient in the primer creates a mold-resistant film that protects the primer itself from mold growth. It does not penetrate existing mold or kill mold cells already on the surface. Marketing language that implies otherwise has spread confusion among homeowners.
What does Kilz Mold & Mildew Primer do?
Two specific things. First, it creates a primer film containing an EPA-registered antimicrobial that resists mold growth on the painted surface afterward. Second, it acts as a stain blocker for the surface discoloration that mold leaves behind, keeping the stain from bleeding through the topcoat. The product is designed for surfaces in high-humidity environments (kitchens, bathrooms, laundry rooms) where mold could otherwise establish on the primer/paint film. It also blocks most stains including water stains, ink, grease, and tannin.
How do you properly use it?
The full process for a previously moldy surface: clean and dry the surface (remove all visible mold with detergent and water, dry completely), apply 1 to 2 coats of Kilz Mold & Mildew Primer per the label, let dry the recommended time (usually 1 hour between coats, 24 hours before topcoat), apply mold-resistant topcoat paint. The primer alone does not provide the full system. The topcoat (also containing mildewcides) completes the protection. Use on properly prepared surfaces, not directly over visible active mold.
What should you do before applying Kilz?
Address the moisture source first; even Kilz cannot prevent mold growth if water is constantly hitting the surface. Remove all visible mold using detergent and water on hard surfaces, or replacing affected drywall and porous materials. Fix any plumbing leaks, ventilation issues, or condensation problems. Let everything dry fully (at least 24 to 48 hours). Then apply Kilz to the cleaned and dried surface. Skipping the cleanup step is the most common mistake; the primer protects the new paint, but does nothing for the underlying mold issue if you skip cleanup.
Kilz does not kill mold despite popular belief. It prevents NEW mold from growing on the primer film but cannot kill existing mold. The right sequence is: remove visible mold, address moisture source, let dry, apply Kilz primer, finish with mold-resistant paint. Skipping the cleanup step is the most common mistake and explains why painted-over mold returns within months. The primer is part of a complete system, not a standalone solution.
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