Before anyone prices a gallon of silicone, one question has to be answered: is the roof underneath dry? Silicone is the coating that tolerates a pond, which makes it the usual answer for a sound membrane that holds water two days after a normal rain and whose owner would rather not tear it off. But the coating is only as good as the surface it bonds to, and it blisters over wet insulation just as surely as any other. A property manager considering silicone should ask for a moisture scan and an adhesion test first, and for a ruler on the pond second.
We apply silicone coating systems over sound low-slope roofs in the Bronx, NY, and when coating is the wrong spend, the written scope says that instead.
A Liquid That Cures to a Flexible Film
Silicone coating is rolled or sprayed on as a liquid and cures by reacting with moisture in the air, leaving a waterproof, flexible film. High-solids formulas build thickness in fewer passes. The film is stable in sunlight, does not chalk, and keeps its elasticity through hot and cold swings. Applied white, it reflects sun and lowers the roof surface temperature.
Its signature trait is its tolerance for standing water, which is where most acrylics soften. Because it goes on as a liquid, it flows into seams, around penetrations and over rough surfaces and leaves a continuous layer with no welding. What it does not do is rescue a failed roof. It extends one that is still sound, and the walk exists to tell the two apart.
Low, Flat Ground in the East Bronx
Parts of the East Bronx are built on marshland and valleys, and the neighborhoods show it. Morris Park, where the Albert Einstein College of Medicine and Jacobi Medical Center sit on the eastern edge, is low-lying and relatively flat, and Baychester is described the same way. Flat ground does not mean a flat roof drains badly, and we make no claim about any one building. It does mean the borough has plenty of owners asking where their water goes.
Ida's September 2021 storm brought 3.15 inches in one hour and 7.13 inches at Central Park overall. A pond that stays more than a day or two after rain also adds weight and ages the seams, so a dated pond log is part of the first visit. A roof that held that water showed its low spots, and silicone is the coating that can sit in them, although a slope that has dipped should still be corrected through ponding water roof repair.
Where Coating Jobs Go Wrong
Four things sink a silicone job. Wet insulation blisters the film from beneath. Dirt, oil or a clashing old coating prevents the bond, and the film peels. Thin coverage at edges and penetrations leaves the film stretched over a corner. And dirt pickup dulls a surface that silicone attracts, which lowers its reflectivity over time.
The freeze-thaw side is kinder. A winter that reaches the -15 F record at the Central Park station flexes any coating, and silicone follows the movement better than a stiff one. A clogged drain does more harm than winter, because it concentrates water on one corner and defeats the coating faster than weather.
The Walk Before the Quote
The walk has a short list, and any item can stop the job. We scan for moisture and confirm with cores. We apply a small patch, let it cure and pull it to test adhesion. We identify what the existing surface is, because not every old coating accepts silicone without primer. We look over seams, flashings and penetrations for repair needs. We check the drains.
Seam and flashing repairs come before any coating. Coat across an open seam and the film bridges it for a season and then splits on the same line. We cut out cracked flashing, re-weld or re-tape seams, reinforce corners with fabric and seal penetrations with a compatible mastic. The scope lists the repairs first, then the preparation, the coating thickness and the expected life. Thickness is a number and not an opinion: we state it in mils, check it with a gauge while the film goes on and record it again at closeout, so a competing bid can be compared on the same basis.
Silicone, Acrylic or a New Roof
A membrane that tests sound and dry is a good silicone candidate, and the roof coating restoration process runs on exactly that path. Widespread moisture points to a commercial roof replacement. On a roof that drains well with a tight budget, acrylic coatings are cheaper and may be enough. A recoat costs a fraction of the first coat because the base is already sealed, which is why the maintenance schedule matters.
Silicone also goes over spray foam and many metal roofs. Some asphalt-based surfaces need a primer first, so we test before committing. Cost follows roof area, repair scope, surface preparation, access and the number of penetrations. No tear-off and no haul-away is what keeps a coating under the price of replacement, and the gap widens on a large, plain roof with few curbs.
Application Days and Occupants
Coating wants dry, mild weather with the dew gone and no rain due until the film sets, so the window runs from late spring to early fall. We start once the dew clears and stop early enough for the film to set. With nothing torn out, dust and noise stay low and the building keeps operating.
Odor is mild, but fresh-air intakes are covered, and the superintendent is told ahead of time which days smell strongest. Near edges the crew rolls instead of spraying, and spraying happens only when the air is still. Rooftop units keep working. The crew coats around the curbs and up their sides, masks nameplates and vents, and when a unit must be lifted, the mechanical contractor sets the lift and the exposed area is coated that same day. Foot traffic stays off the roof for a day or more after the last coat.
Records and Reflectivity
A white silicone finish doubles as a cool roof installation, which can matter on a top floor that runs warm. We record the product, thickness and dates and read the membrane manufacturer's terms before the proposal is written, since some warranties require approved coatings. The Department of Buildings distributes the 2022 NYC Construction Codes. Filings go there.
After cure we photograph every edge and penetration and send thickness readings. The maintenance calendar gets a recoat date, and a commercial roof inspection once the first winter has passed shows whether the film survived freeze and thaw.
Commercial Roofing Questions
Why pick silicone over acrylic on a roof that ponds?
Many acrylics soften or wash out under standing water, and silicone does not. Correcting the low spot remains the lasting cure, and the coating holds the line until that work is scheduled.
Can a roof that has leaked before be coated?
Yes, once the wet insulation has been found and removed. A thermal scan and cores locate the soaked sections, which are cut out and replaced before one continuous coat covers old and new alike.
Does silicone get dirty?
It tends to hold dirt, which dulls the surface and cuts reflectivity. Washing it once a year brings most of that back, and a roof under trees or near exhaust may need more frequent cleaning.
How thick is the coat?
The product and the roof set the number, the proposal states it, and we check it during application. Edges and penetrations get extra, since thicker film lasts longer.
Will a coating void my roof warranty?
It can change the terms. The membrane manufacturer writes them, and we read them before the scope is final.
Send the Surface and the Ponding Spots
Tell us the building type, the roof age, what the surface is now and where water sits. We will scan for moisture, test adhesion and write up whether silicone fits.
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