Seams, Fasteners and Penetrations Before the First Coat
A coating is a skin, and a skin bridges only what is beneath it. Open seams, backed-out fasteners, split pitch pockets and cracked flashings do not heal under a coat of silicone. They show through it, and then they leak. So every seam gets sealed or taped with reinforcing fabric, every fastener head is reseated or covered, and every curb, pipe and drain base is detailed before the field coat goes on. On a metal roof this includes the laps, the ridge cap and the screw heads, which expand and contract more than any other part of the panel.
The sheet metal gets the same attention. Counterflashing is reset into the reglet, cracked sealant joints are cut out and tooled again, and parapet copings are repaired or rebuilt so water cannot run behind the new surface. A silicone coating over failing flashing details is a roof that looks new for a year and leaks in the first winter storm.
Cleaning, Primer and Dry Mil Thickness
The application starts with a thorough wash and a dry, clear forecast. Silicone cures by moisture in the air, so it tolerates a humid morning better than most coatings, but it cannot go onto a wet surface or take rain before it has set. We choose the primer for the substrate in front of us, then apply the coating in the thickness that the manufacturer specifies, measured in dry mils with a gauge, not judged by eye. A coat that is too thin costs more later than the material it saved.
Spray covers large open fields quickly, while rollers and brushes work edges and tight spots. We check thickness as we go and walk the finished surface for pinholes before we leave. On an occupied building the roof stays in service the whole time, with no tear-off debris and no open deck over the tenants.
Dirt Pickup and Recoating
Silicone has one habit owners should know about: it is slightly tacky on the surface and attracts dirt. A bright white roof grows dull over time as dust, soot and pollen settle into it, and the reflectivity that earned its cool roof value slowly drops. Washing the roof once or twice a year puts much of that brightness back, and we build that cleaning into maintenance visits.
When the coating finally thins, the recoat is a wash and a fresh layer of silicone, and it bonds to itself well. That is the case for choosing silicone carefully on day one, because it commits the roof to silicone for good. For owners weighing whether coating makes more sense than a new membrane, the comparison belongs on the actual roof, which is where coating restoration begins, and on a foam roof silicone is the usual protective topcoat over spray polyurethane foam.
Ponding Water, Winter Rain and Cool Roof Rules
Pasadena roofs are asked to handle two extremes in the same year. A recorded June high of 113 degrees shows how hard the sun can bake a dark membrane until the seams crawl, and the San Gabriel Mountains give the city about six inches a year beyond what downtown Los Angeles gets, with February the wettest month, so water can lie in every low spot after a winter storm. Silicone copes with both. A white surface can reflect sunlight, and a product specified for ponding may be an option where water cannot be fully redirected. That makes it a common choice on flat roofs with ponding water that cannot be fixed with new slope.
The state's cool roof numbers are measured after aging, and a new roof or qualifying alteration may need to meet them. We select a white silicone only when its published aged values meet the applicable threshold, and cool roof installation has to allow for how far the reading falls as the surface collects dirt. Where a roof sits in a mapped fire hazard zone, we confirm the Class A assembly before we coat.
Commercial Roofing Questions
Why would a coating job fail on a roof that still looked good?
Usually because the roof underneath was wet, dirty or loose in places that could not be seen from the walkway. Wet insulation under the membrane, open seams and fasteners that have backed out all show through a new coating within a season or two. We survey the roof and cut test samples before coating, so the plan rests on what is actually under the surface.
Does a silicone coating make sense on an office roof on South Lake Avenue?
It does when the roof is still dry beneath and the deck is sound. Office buildings along Lake Avenue compete in the Burbank-Glendale-Pasadena Tri-Cities market, where vacancy stood at 26.1 percent in the last quarter of 2025, and an owner on South Lake Avenue in that market has reason to weigh a coating that extends a roof against the cost of replacing it. We tell owners when a roof is too far gone for it.
Can silicone go over a metal roof that is rusting?
Yes, once the rust is removed and the panel is primed with a rust-inhibiting coat. We scrape or wire-brush the worst spots, replace failed fasteners and treat the laps. A coating can preserve suitable panels when preparation and adhesion checks support that approach, and it can lead into a full metal roof retrofit later if the structure calls for it.
How slippery is a silicone roof, and is that a safety issue?
Silicone is slick when wet, which matters for any crew servicing rooftop equipment. We add walkway pads or granules along service routes and keep a clear path to each unit before the job is signed off.
What happens if the old roof has been coated with something else already?
The first step is finding out what is on it, and the test patch tells us. An old acrylic can be primed and coated with silicone if it passes adhesion tests, but a roof with several layers of unknown coatings may fail the test. When that happens we look at stripping the coating, recovering the roof or replacing it, and we put the options in writing.
