Painting a garage door is a cost-effective way to refresh a home’s exterior, but the durability and final appearance of the finish rest almost entirely on the quality of the preparation. A poorly prepped surface will cause even the highest quality paint to blister, flake, or peel prematurely. Proper surface preparation is a sequential process that ensures the new coating can form a reliable mechanical and chemical bond with the substrate. Taking the time to execute each preparatory step guarantees a long-lasting, smooth, and professional result.
Deep Cleaning the Surface
The first step in any exterior painting project is eliminating all surface contaminants that interfere with paint adhesion. Garage doors accumulate grime, oil, and atmospheric dirt that a simple rinse cannot fully remove. Using a heavy-duty cleaner like trisodium phosphate (TSP) or a specialized TSP substitute is necessary to effectively de-grease the surface and strip away chalking from old, oxidized paint. A common dilution for a general cleaning solution is approximately one-half cup of TSP powder dissolved in two gallons of warm water.
For areas affected by mildew, a slightly stronger solution incorporating bleach, such as one cup of TSP mixed with three quarts of warm water and one quart of bleach, should be applied. The cleaning solution must be worked into the door’s surface with a stiff brush or sponge, paying attention to recessed panels and grooves. After scrubbing, the door must be rinsed thoroughly with clean water to remove all detergent residue. Allowing the garage door to dry completely is a final, non-negotiable step; moisture trapped beneath the new coating will cause bubbling and eventual failure.
Repairing Flaws and Ensuring Adhesion
Once the door is clean, the surface must be corrected for imperfections and textured to accept the new paint layer. Any existing loose or peeling paint must be removed with a scraper or putty knife, and the edges of the remaining old paint should be feathered with sandpaper to create a smooth transition. This process eliminates weak points where the new paint could lift and ensures a uniform final appearance. After scraping, the entire door surface should be lightly sanded to create a mechanical profile for the paint to grip.
A fine-grit sandpaper, such as 220-grit, is used to lightly scuff the surface without creating deep scratches. On metal doors, any visible rust must be loosened with a wire brush and completely removed. These areas should then be spot-treated with a rust converter or a specialized rust-inhibiting primer to neutralize any remaining corrosion and prevent its spread. Dents and deep scratches should be filled with an exterior-grade filler—such as Bondo for metal or wood filler for wood doors—and sanded flush with the surrounding surface once cured.
Masking and Protecting Hardware
The final preparatory step involves protecting any areas that are not intended to be painted from splatter and overspray. This measure ensures clean, sharp paint lines and prevents paint from binding surfaces that need to remain flexible or operational. High-quality painter’s tape should be used to carefully outline the edges of the trim, windows, and weather stripping.
Hardware such as hinges, handles, and locks must be covered with a combination of painter’s tape and plastic wrap. For the surrounding areas, plastic sheeting or drop cloths should be secured to the driveway and any adjacent walls or siding to guard against accidental overspray. Press the tape firmly along its edges, especially where it meets the door surface, to create a tight seal that prevents paint from bleeding underneath.