How to Paint Aluminum Siding

Understanding what causes the deterioration helps you address it correctly before painting.

• UV exposure breaks down the original factory finish and any previous paint layers, causing oxidation and chalking
• Humidity and temperature swings common in the Northeast cause the metal to expand and contract, which stresses paint bonds over time
• Improper surface prep on a previous paint job means new paint was applied over chalk or contamination, shortening its lifespan
• Use of the wrong paint type - oil-based or interior-grade products - which cannot flex with metal movement
• Physical damage from hail, debris, or ladders that chips through to bare aluminum, creating spots where moisture and rust can develop

Step 1: Choose the Right Day
Avoid painting in direct intense sunlight, when temperatures are below 50 degrees F or above 90 degrees F, or when rain is expected within 24 hours. Overcast, mild days with low humidity produce the best adhesion. Check the forecast for a two-day window of dry weather.

Step 2: Protect Surrounding Areas
Cover landscaping, walkways, windows, doors, and any trim you do not plan to paint with drop cloths and painter's tape. Remove or mask off light fixtures, shutters, and downspouts where possible.

Step 3: Wash the Siding Thoroughly
Mix TSP or a similar degreasing cleaner per the product label and scrub the entire surface with a stiff brush, working from top to bottom. A pressure washer set to a low or medium pressure can speed things up - avoid high pressure, which can dent or bend aluminum panels. Rinse completely and allow the surface to dry for at least 24 hours.

Step 4: Remove Chalk and Loose Paint
Rub a rag across the surface. If chalk transfers, you need to remove it. Sand chalky or oxidized areas with 80-to-120-grit sandpaper or a wire brush until the surface has some texture and transfers minimal residue. Wipe away dust with a damp cloth and let dry fully.

Step 5: Spot-Prime Any Bare Metal
Anywhere you can see raw aluminum, apply a metal bonding primer to seal the exposed area before priming the full surface. This prevents rust staining from bleeding through your topcoat.

Step 6: Apply a Full Coat of Bonding Primer
Using a roller for field areas and a brush for edges and joints, apply an even coat of bonding primer rated for aluminum or metal. Work in manageable sections and maintain a wet edge to avoid lap marks. Let the primer dry completely according to the manufacturer's drying time before moving on.

Step 7: Paint the First Topcoat
Apply 100% acrylic exterior paint using a roller, brush, or sprayer. Start at the top and work downward. Keep strokes consistent with the direction of the panels. Thin, even coats bond better than one thick coat and reduce the risk of drips or sagging.

Step 8: Apply the Second Topcoat
Allow the first coat to dry fully - typically four to six hours depending on conditions - then apply a second coat. Two coats give you even coverage, better color depth, and a more durable finish. Once dry, remove painter's tape carefully at a 45-degree angle to get a clean line.

• Homes built before 1978 may have lead paint. If you suspect lead, have the surface tested before sanding. Thermo-Seal is an EPA Lead-Safe Certified Firm, and for older homes, professional handling is often the safer call.
• Always set ladders on firm, level ground and have a second person nearby when working at height.
• Wear safety glasses and a respirator rated for paint vapors - not just a dust mask.
• Keep paint and primer away from drains and landscaping. TSP and paint runoff can harm plants and waterways.
• Do not use open flames or power tools that generate sparks near open cans of solvent-based primer.
• Never lean or reach too far from a ladder. Reposition it frequently rather than stretching.

Sometimes deteriorating paint is a symptom of an issue that goes beyond aesthetics. Watch for these red flags that suggest a professional assessment is needed:

• Dents, cracks, or buckled panels that will not hold paint evenly and may compromise moisture protection
• Widespread rust staining under peeling paint, which indicates long-term moisture infiltration
• Soft or rotted sheathing discovered when panels are temporarily lifted - a sign that water has been getting behind the siding
• Paint peeling repeatedly in the same spot after multiple repaints, which can point to air leakage or condensation issues behind the wall
• Damaged caulking around windows, doors, or penetrations allowing water to track behind the siding
• Significant gaps, nail pops, or loose sections that compromise the siding's ability to protect the structure