Painting a rusty metal roof can help restore and protect it, extending the roof’s lifespan. However, proper preparation and using compatible paint products designed for metal and rust is key to achieving long-lasting results. This comprehensive guide will walk you through all the steps for prepping, priming, and painting a rusty galvanized metal roof.
This guide will walk through all the key steps for prepping, cleaning, priming, and painting a rusted metal roof. We’ll also discuss common problems and solutions for dealing with badly rusted or leaking metal roofing. Let’s start by going over what supplies you’ll need.
Supplies Needed
Painting a metal roof requires having the right combination of tools, cleaners, primers, and paints on hand. Here’s an overview of the recommended supplies:
- Safety gear – goggles, gloves, mask/respirator
- Ladder – for safely reaching the roof
- Wire brush – for removing loose rust
- Sandpaper – 80-100 grit for sanding smooth rusted areas
- Paint scraper – for removing flaking paint
- Metal prep solutions – vinegar, TSP substitute, ammonia
- Rags & buckets – for cleaning roof surface
- Rust-inhibiting metal primer – compatible with galvanized or rusted roofs
- Elastomeric roof paint – top coat designed for metal roofing
- Paintbrushes – various sizes for cutting in edges
- Paint rollers & handles – for quickly coating large areas
- Paint trays – to hold primer and paint for rolling
- Drop cloths – for protecting vegetation or surfaces below
Remove Loose Rust and Flaking Paint
Before painting, it’s essential to remove any loose rust, paint, or corrosion from the roof surface. This allows the primer and paint to adhere properly.
Use a stiff wire brush to scrub off all loose rust and flakes of paint. Aim to get down to the bare metal substrate. Be sure to wear thick gloves and protective eyewear when wire brushing.
For smoother rusted areas, sandpaper (80-100 grit) can help thoroughly scuff and dull the surface. Also use a paint scraper to chip off any large pieces of peeling paint.
Removing all the loose material will promote better adhesion when you apply the primer. Thoroughly sweep or vacuum up any rust debris when finished brushing and scraping.
Clean and Degrease the Metal Roof
After removing all the loose rust and paint, the next step is to clean and degrease the roof surface. This removes oily residues and further prepares the metal for painting.
Use the following steps to properly clean and prep the metal:
- Vinegar: Wipe down the metal roof with a vinegar solution (1 part vinegar to 2 parts water). The mild acid in vinegar helps neutralize and remove remaining rust.
- TSP substitute: Mix a non-phosphate TSP substitute with water per label instructions. Scrub roof surface with this solution to degrease the metal.
- Ammonia: For heavily oxidized areas, use a 50/50 mix of ammonia and water. This helps etch the surface for better adhesion.
Be sure to thoroughly rinse the roof with clean water after degreasing. Allow the metal to fully dry before applying primer.
Proper cleaning removes oils, rust residues, and weathering that could interfere with paint bonding. It’s a critical step that helps ensure long-lasting results from your fresh paint job.
Apply Rust-Inhibiting Metal Primer
Once the metal roof surface is prepped, cleaned, and dry, it’s ready for a coat of primer. It’s crucial to use a primer specifically formulated for galvanized metal or rusted roofs. The right primer will provide a protective base layer and prevent future rust.
Look for these key features when selecting a primer:
- Rust-inhibitive – contains rust inhibitors and metal oxides to prevent corrosion under the paint.
- Etching primers – contain phosphoric acid to etch bare metal for better adhesion.
- Cured coating – dries into a tough, protective base layer over existing rust.
Popular metal primer brands include Rust-Oleum Stops Rust Protective Enamel and KILZ Adhesion High-Bonding Interior/Exterior Latex Primer.
Thoroughly stir the primer before using. Apply an even coat across the entire roof surface using a paintbrush, pad applicator, or paint sprayer. Work the primer into any pitted areas.
Allow the primer to fully dry per the manufacturer’s recommended dry time before applying any top coats (usually at least 24 hours). The primer should leave a slightly textured surface for the paint to grip.
Priming before painting provides maximum rust protection and prevents peeling. It helps the paint better withstand the roof’s movements and extreme weather.
Apply Elastomeric Roof Paint
Once the primer has fully cured, the final step is applying one or more coats of elastomeric roof paint. Elastomeric paints are thick, flexible coatings designed to expand and contract with metal roofing.
Look for paints that offer these key benefits:
- Rubber-like elasticity – allows the coating to stretch and move with the roof.
- UV-resistant – protects against sun damage and fading.
- Waterproofing – seals out rain and moisture to prevent rust.
- Reflective pigments – deflect heat to keep roofs cooler.
- Rust inhibitors – contain additives to prevent corrosion under the paint.
- Mildew resistance – prevents ugly black streaks from mold growth.
Quality elastomeric roof paint brands include KST Coatings and KARNAK. Be sure to use exterior-grade acrylic latex paints designed specifically for metal roofing.
As with priming, thoroughly mix the paint before using and make sure conditions are dry before applying. Use paintbrushes to “cut in” along edges and seams. Then quickly roll larger sections using a 3/4″ nap roller.
Apply 2-3 coats to achieve full coverage, allowing each coat to dry between applications fully. The drying time will depend on humidity and temperature.
Finish with angular roof granules sprinkled into the final coat to create an attractive, protective finish.
Alternative Paint Options for Metal Roofs
While elastomeric coatings are ideal for their rubber-like flexibility, several other commercial paint options work well for refinishing metal roofs:
- Aluminum-based paint – Contains aluminum pigments for metallic sheen and rust protection. Brands like Kool Seal save time with a reflective primer and paint in one.
- Urethane coatings – Offer a durable, industrial-grade finish like truck bedliners. Excellent moisture and rust resistance.
- Acrylic paint – Water-based acrylic latex paint provides good weather resistance when combined with a rust-inhibiting primer.
- Silicone paint – Based on silicone resins for flexibility and water resistance. Performs well but can be costlier.
- Epoxy paint – Two-part coatings offer extremely durable, protective finishes resistant to chemicals and corrosion. Require proper mix ratios and limited pot life.
Whichever paint you choose, be sure it’s specifically engineered to withstand outdoor weathering. Carefully follow all product instructions for proper application and drying times.
Solutions for Severely Rusted Roofs
For metal roofs suffering from extensive rust and deterioration, painting alone may not be enough. Severe corrosion can weaken and perforate the roof sheets, leading to leaks.
In cases of substantial rust-through, these added products and steps can help repair heavily rusted sections before priming and painting:
- Rust converters – Also called rust transformers, these chemically convert rust into a protective polymer coating. Rust-Oleum Rust Reformer or Loctite Extend Rust Neutralizer are top options. After converting the rust, prime and paint as usual.
- Rust encapsulators – Sealants like Clear Coat Rust Grip form a thick, flexible barrier over corroded areas. Helps bridge small holes or gaps from rust-through.
- Metal patches – For larger holes or leaks, welding or riveting metal patches provides a permanent repair. Seal edges with caulk before painting.
- Roof sealants – Elastomeric sealants like KST Coatings Rubr-Seal or Geocel 2300 help seal around fasteners, seams, and penetrations prone to leaks.
- Foam fillers – Gaps and holes under 3 inches wide can be filled with polyurethane roofing foam before coating. Provides insulation too.
Don’t just paint over substantial rust problems or the issues will continue. Make proper repairs first, then prime and paint for long-lasting protection.
When to Avoid Painting a Metal Roof
While painting a worn metal roof can preserve it, there are certain situations when a roof may be beyond restoring with paint. Avoid painting if you see these issues:
- Extensive rust-through – Holes and perforations from corrosion are too severe for paint to repair.
- Thick layers of rust – Years of rust buildup may require full roof replacement vs. painting.
- Brittle, damaged panels – Cracking, splits, and erosion from long-term weathering.
- Previous paint failure – If paint is heavily peeled, chipped, or delaminating due to improper surface prep.
- Poor original galvanizing – Zinc corrosion protection compromised at time of installation.
- Underlying moisture issues – Paint will fail if leaks causing rust are not properly addressed.
- Incompatible materials – Certain plastic and rubber membranes resist paint bonding.
If the roof shows signs of extreme deterioration instead of surface rusting, a full roof replacement may be needed. Contact a reputable roofer for an assessment.
Prep Tips for a Long-Lasting Paint Job
Proper prep work is the key to achieving great results from painting a rusty metal roof. Keep these best practices in mind:
- Thoroughly remove all loose rust and flaking paint so primers and paint can adhere.
- Properly clean and degrease the metal surface after wire brushing, sanding, and scraping.
- Allow sufficient drying time after cleaning and between paint coats. Damp metal prevents good bonding.
- Apply quality primers and paints designed for rust protection and metal roofing. Follow all product instructions.
- Address any significant rust-through patches or leaks before priming and painting.
- Paint on dry, clear days when temps are above 50°F to allow proper curing.
- Maintain a wet edge and work in sections to prevent lap marks in the finish coat.
Great prep establishes a sound foundation. Patiently following each step leads to optimal, long-lasting paint results.
Maintaining a Painted Metal Roof
Once your metal roof is properly prepped, primed, and painted, conduct annual inspections and maintenance to maximize its lifespan. Here are some metal roof care tips:
- Inspect for any new rust spots annually and wire brush them before they spread. Spot prime and paint as needed.
- Clean painted roofs yearly using a power washer on low pressure. Avoid abrasive cleaners.
- Check and reseal any fastener penetrations that allow moisture under the roofing.
- Watch for dented, warped, or perforated panels which indicate hail or wind damage.
- Remove debris and leaves from valley areas and drip edges where moisture collects.
- Recoat the roof every 3-5 years or when the paint surface appears dull and weathered.
- Address any exterior moisture sources like poorly draining gutters that accelerate roof rusting.
Staying on top of basic maintenance preserves your roof’s paint job and prevents costly rust damage.
Conclusion
Restoring an aging, rusty metal roof through proper prep and painting can add many extra years of life to the roof. Utilizing rust-inhibiting primers and coatings designed for metal substrate provides maximum rust protection and weather resistance.
However, the project’s success depends heavily on thorough surface cleaning and removal of all corrosion before painting. When done right, a fresh coat of protective paint can make a rusty roof look brand new while saving thousands of dollars compared to full roof replacement. Keep the tips in this guide in mind for top-quality, long-lasting paint results
