Why use Silicone Waterproofing
It What it is
A silicone roof coating is a liquid-applied, moisture-curing elastomer that dries into a seamless, rubbery membrane over your existing roof. It’s typically bright white (highly reflective), but can be tinted. Unlike patch-by-patch fixes, it forms one continuous waterproof layer.
Where it’s used
Low-slope and flat roofs
Substrates: metal, modified bitumen/BUR (often with a bleed-block primer), single-ply (TPO, EPDM, PVC—usually needs a specific primer/adhesion promoter), and spray polyurethane foam (SPF)
Why people choose silicone
Excellent ponding-water resistance: Silicones tolerate standing water better than acrylics.
UV durability: Resists chalking and sun degradation; keeps flexibility for years.
Cool-roof performance: High reflectivity/emissivity can lower surface temps and cooling loads.
Seamless & flexible: Bridges small movement and thermal cycling.
Low VOC (high-solids systems): Many meet strict air-quality rules.
Limitations to know
Dirt pick-up: Silicone films can attract dust, which can dull reflectivity (cleaning helps).
Lower tear/abrasion resistance than urethanes: Not ideal for heavy foot-traffic areas unless reinforced and granulated.
Adhesion is substrate-specific: Single-plys, aged asphalt, or oily/contaminated surfaces often need primers; adhesion tests are important.
Slippery when wet: Walk pads or broadcast granules recommended along paths.
Repairs later usually require silicone again: Other coatings don’t stick well to cured silicone without special prep.
Moisture in the roof must be addressed first: Coatings aren’t for trapping wet insulation or structural leaks.+
When silicone is (and isn’t) a good fit
Great fit if: the roof is mostly dry and sound, you want strong ponding-water resistance and long UV life, and minimal disruption.
Less ideal if: constant heavy foot traffic, persistent oil/grease contamination (restaurants/industrial stacks) without added protection, or widespread saturated insulation that needs replacement.
Quick comparison with other coatings
Acrylic: cost-effective and very reflective, but dislikes ponding water; often needs positive drainage.
Urethane: tougher and more abrasion-resistant (good for traffic areas), but can be pricier and may yellow under UV; commonly used as a base with silicone topcoat.
SEBS/Asphaltic: good on certain bitumen roofs, but typically not as UV-stable as silicone.
The installation workflow (high level)
Assessment & testing
Inspect flashing, seams, fasteners, penetrations.
Perform a moisture survey (infrared, core cuts, or impedance) to locate wet insulation; replace wet areas.
Surface prep
Pressure-wash (commonly 2,500–3,500 psi) with detergent; remove rust and loose coatings.
Tighten/replace fasteners; repair blisters, splits, and rusted sections.
Detailing
Seal seams, laps, fasteners, and penetrations with silicone/urethane mastic.
Embed polyester fabric where movement or gaps are larger.
Priming (as required)
Use adhesion primers for single-ply membranes, and bleed-block primers over asphaltic roofs to prevent staining.
Coating application
Spray or roller-apply in two passes, typically cross-hatched (perpendicular) to reach target wet film thickness; verify with a wet-mil gauge.
Add walk pads or broadcast granules into the second coat where foot traffic is expected.
Cure & QA
Skins in ~1–3 hours; full cure often 8–24 hours (faster with humidity; it’s a moisture-cure chemistry).
Final inspection for pinholes/holidays; check adhesion and finished dry film thickness.
