Which term describes the underlying surface material being repaired or painted?

• A. Topcoat
• B. Primer
• C. Substrate
• D. Sealer

Answer: (C)

The underlying surface material being repaired or painted is the substrate. It’s the actual body material under the finish—steel, aluminum, plastic, or fiberglass—that coats are applied to. Knowing this helps you plan the steps: you repair the substrate first, then you may apply a primer to improve adhesion and corrosion resistance, possibly use a sealer to address porosity or create a uniform base, and finally apply the topcoat for color and protection. The other terms refer to coatings applied on top of the substrate: the topcoat is the visible color layer, primer helps the finish adhere to the substrate, and sealer prepares or seals the substrate surface before color.