Roof Coating and Restoration

A roof coating is a liquid applied in one or more coats over a roof surface, where it dries or cures into a thin, monolithic, fully adhered film. On low-slope roofs coatings are used both as the protective top layer of systems such as spray polyurethane foam, and as a "restoration" treatment that renews an ageing membrane or metal roof without tearing it off.

Purposes

• waterproofing and sealing minor defects on a structurally sound roof
• protecting the substrate from UV, heat, rain and hail
• creating a reflective cool roof that lowers surface temperature and cooling loads
• providing a wearing surface, sometimes with embedded granules

Coatings are not normally traffic-bearing; trafficked balconies and decks use dedicated deck-coating systems.

Main types

• Acrylic: water-based, economical, highly reflective; not usually warranted for ponding water.
• Silicone: high-solids, very UV-stable, tolerant of ponding in many products; dirt pick-up and recoat adhesion need attention.
• Polyurethane: tough and abrasion-resistant, aromatic and aliphatic grades.
• Polyurea, butyl, SBS/styrene-butadiene, PVDF.
• Asphalt and coal-tar based coatings for bituminous roofs.

Thickness

Dry film thickness ranges from about 0.075 mm (3 mils) to over 1 mm (40 mils). On SPF roofs typical coatings are 0.5-1.0 mm (20-40 mils).

Restoration process

A typical restoration includes a roof survey (often with moisture scanning to find wet insulation), removal of wet areas, cleaning, repairs to seams and flashings, primer where needed, reinforcing fabric at details, and coating applied to a specified thickness. Properly maintained coatings need periodic recoating; on SPF roofs this is usually every 10-20 years.

Limitations

Coatings cannot fix a roof with saturated insulation or structural problems. Coating asphalt shingles and some built-up roofs needs caution because of trapped moisture. Light-coloured coatings show dirt and biological growth more readily in warm, humid climates.