Roof coatings & sealing for flat and metal roofs

A roof coating is a liquid-applied membrane — usually silicone or acrylic — rolled or sprayed over an existing flat or metal roof to seal it, stop leaks and reflect heat. On a roof that’s still structurally sound, a coating can add many years of life for a fraction of what a tear-off costs. On a roof that’s already failed underneath, it only hides the problem for a while.

Where a coating makes sense

• Metal roofs on commercial and industrial buildings, pole barns and garages — once the rust is treated and the seams and fasteners are sealed.
• Mobile and manufactured homes. The metal roofs on single-wides and double-wides respond especially well to sealing and coating.
• Aging single-ply and modified bitumen roofs that are still watertight, with dry insulation underneath.
• Roofs you need to keep for a few more years — ahead of a sale, a renovation, or a planned replacement in the budget.

When it doesn’t

Be wary of anyone who says a coating fixes everything. It’s the wrong answer when:

• The insulation under a flat roof is wet. A coating seals moisture in, and the roof keeps rotting from below.
• A metal roof is rusted through across large areas rather than surface rust.
• Water ponds for days. Some coatings handle ponding better than others, but none fix poor drainage.
• The roof has already been patched and coated more than once and is still leaking.

A moisture check and a close look at the seams and fasteners tells you whether you’re a candidate before you spend anything.

How a coating job is done

1. Inspect and test. Look at every seam, fastener, flashing and penetration, and check for wet insulation on flat roofs.
2. Clean. The roof is power-washed so the coating bonds to the roof, not to dirt.
3. Repair. Failed seams are reinforced, loose or rusted fasteners replaced or sealed, flashings and penetrations repaired.
4. Prime where the product and the surface call for it — rusted metal and some older membranes need it.
5. Coat. Applied in one or more coats to the thickness the product requires. Thickness is what makes a coating last.
6. Check. A final walk to catch thin spots and make sure every detail is sealed.

Silicone or acrylic?

Both are common. Silicone generally holds up better where water sits and weathers slowly; acrylic is often less expensive and easy to recoat but doesn’t like ponding water. The right one depends on the roof underneath, how it drains, and the budget. Our guide to roof coatings for flat and metal roofs goes deeper.

Coatings are one of several options for a tired flat or metal roof — see flat roofing and commercial roofing for the others. Request a free estimate and we’ll tell you honestly whether your roof is a candidate.