Coating metal roofing with a sealant is an effective way to help prevent common leaks, forestall rust, and extend the life of an aging roof. Some products are also recommended for additional protection on newly installed metal roofing. Most roof coatings are applied similarly to paint and are elastomeric, meaning they remain flexible enough to stretch and shrink with the normal expansion and contraction of metal roofing. Preparation and application methods vary, so be sure to follow the product instructions carefully. Many seal-coat systems involve multiple stages and may include sealing joints and other vulnerable areas with compatible caulk or sealant, followed by a primer and one or more topcoats of sealer.
Inspect the Roof
Clean the entire roof thoroughly with a garden hose and nozzle, or pressure washer, to remove dirt, dust, leaves and other plant debris. Let the roof dry completely.
Carefully inspect the roof for damage, extensive rust, or other problems that may warrant replacing roofing panels and other materials, such as flashing and trim pieces. If roof leaks have been persistent, also inspect the wood framing of the roof structure for rot and other signs of potential weakness
Replace damaged and deteriorated roofing materials, if necessary, following the manufacturer's instructions. Consult a qualified building professional to inspect and assess any problems with the roof structure.
Prepare the Roof
Replace all loose or missing screws or nails securing the roofing to the underlying structure. Use the same type of fastener as the originals to prevent galvanic action, which is corrosion due to contact between dissimilar or incompatible metals. Replace fasteners with badly deteriorated rubber (neoprene) washers, if applicable.
Remove rust from metal roofing materials with a wire brush. Areas with extensive corrosion, particularly red rust on galvanized steel roofing, may have to be replaced. Clean all dust and debris from treated areas.
Seal joints between roofing panels, along flashing and trim, and around fastener heads, as directed by the sealant manufacturer. Some systems call for sealing seams with roofing tape and a compatible adhesive/sealant.
Apply the Coating
Apply a coat of primer or base coat to the entire roof, if applicable, using a paintbrush, roller or spray equipment, following the manufacturer's instructions. Let the primer coat dry as directed.
Seal the roof with a topcoat of sealant, again using a brush or other paint applicator. With some sealant systems, you apply the topcoat perpendicularly to the base coat. Let the sealant dry as directed.
Apply the second topcoat of sealant, if applicable, and let it dry as directed.