Yes, a top coat is strictly necessary. The Rust-Oleum Home system is a 2-step process where Step 1 (the Base Coat, such as Charcoal Gray) provides the color, and Step 2 (the Rust-Oleum Home Top Coat) is required to seal the surface and deliver scratch, scuff, and stain resistance. Leaving the base coat without a top coat will leave the floor unprotected and prone to rapid wear.