Ponding water
Silicone shrugs it off — it’s the reason we spec it on slow-draining roofs. Acrylic re-emulsifies under standing water and thins out at the low spots. If water sits past 48 hours, acrylic is off the table.
Ponding water on flat roofsSilicone vs Acrylic, at a glance
Silicone cures with moisture, tolerates standing water and holds up where a St. Louis roof drains slowly. Acrylic cures by evaporation, costs less, reflects well and re-coats easily — but it softens and washes off under ponding. Either one only works over a dry, sound substrate, so a moisture scan and core samples come first. John Beal Roofing prices both. Call (314) 429-6000.
A coating is not a roof. It’s a monolithic membrane sprayed or rolled over one you already have, and it buys you ten to twenty years if the roof underneath is dry and structurally fine. If the insulation is wet, a coating traps that water and you’ve spent real money making the tear-off worse.
So the first question isn’t silicone or acrylic. It’s whether this roof is a coating candidate at all. Once it is, the choice mostly comes down to how your roof drains and how much you want to spend.
The Real Differences
Six Things That Actually Separate Them
How they cure
Silicone is moisture-cure, so Missouri humidity actually helps it. Acrylic is evaporative — it needs 50°F and rising, low dew point and a dry night behind it. A surprise thunderstorm four hours after an acrylic pass can wash it into the parking lot.
Mil thickness
Silicone typically goes on at 20 to 25 dry mils in one or two passes. Acrylic wants 25 to 30 dry mils, usually in two or three. We record wet mil readings as the crew works, not just at the end.
Dirt pickup
Silicone stays slick and grabs dirt, so that bright white fades toward gray within a couple seasons and reflectivity drops. Acrylic stays cleaner and keeps more of its solar reflectance.
Re-coating later
Acrylic re-coats easily — wash it, prime the failed spots, spray again. Silicone only bonds to silicone, so a silicone roof is a silicone roof from then on. That matters for a building you’ll own for thirty years.
Cost per square
Acrylic material runs cheaper per gallon and you can put it down faster. Silicone costs more up front and needs fewer coats. On a dry, well-drained roof acrylic usually wins on price; on a wet-sitting roof silicone wins on not failing.
Commercial roof coatings
Before Anyone Sprays
The Work That Happens First
We scan the roof for wet insulation and we pull cores. A coating over saturated polyiso is money burned — the water has nowhere to go and the deck keeps corroding under a sealed lid. Any wet area gets cut out and replaced with matching-thickness board before a drop of coating goes down.
Then the roof gets cleaned. Power wash, sometimes with a cleaner for grease near kitchen exhaust, and it has to be dry before primer. Grease and silt are the two most common reasons a coating peels in year two, and both are preventable with an extra day of prep.
Every seam, curb, drain and penetration gets reinforced — polyester fabric embedded in a base pass, then coated over. That detail work is most of the labor on a coating job and it’s the first thing a cheap bid cuts.
We also run an adhesion test patch on aged membrane. EPDM in particular needs the right primer, and a weathered TPO surface has to be scrubbed back. A 10x10 test square and a pull test beats guessing on 40,000 square feet.
Which One We’d Spec On Your Building
Slow drains, tapered insulation that never quite worked, birdbaths that hold after a storm — silicone. A well-pitched roof with clean drains, a tight budget and a plan to re-coat in twelve years — acrylic. A roof with heavy kitchen grease anywhere near the exhaust fans — usually neither, until we’ve solved the grease. And a roof with more than about twenty-five percent wet insulation isn’t a coating job at all, it’s a tear-off.
Warranty Terms And What Voids Them
Manufacturers write coating warranties at 10, 15 and 20 years, and the term is tied directly to how many dry mils you put down. Skimp on thickness and the warranty drops or disappears. The common exclusions in Missouri are unrepaired ponding, foot traffic without walk pads, and new penetrations cut in by an HVAC contractor who never told anybody. Keep a maintenance file and keep other trades off the roof without notice.
Weather Windows Here
Our coating season realistically runs April into October. Acrylic is the fussier of the two — we watch the dew point, not just the daytime high, because a cool September night can leave film that never fully cures. Silicone gives us a wider window and can handle an early-morning dew that would ruin an acrylic pass. On a tight schedule that flexibility is worth the price difference by itself.
Related: ponding water on flat roofs, tear-off vs recover and spray foam roofing.
Common Questions
How long does a roof coating last?
Ten to twenty years depending on the system, the mil thickness and how the roof drains. The warranty term follows the thickness, so a 20-year coating is a thicker coating, not a different bucket.
Can you coat a roof that ponds water?
Silicone, yes. Acrylic, no. But if the ponding comes from crushed insulation or a failed drain, we’d rather fix the drainage than coat around it.
Will a coating stop an active leak?
Only if we find and repair the source first. Coating is a restoration system, not a leak repair, and spraying over a wet roof seals the water in.
Is a coating cheaper than replacing the roof?
Usually a fraction of a tear-off, and it can often be expensed rather than capitalized. Ask your accountant — that treatment is why a lot of owners choose it.
Do you offer free inspections before recommending one?
Yes. We’ll scan for wet insulation, pull cores if needed and tell you honestly if the roof is past the point where coating makes sense.
Free Roof Coating Evaluation
Tell us about the property and a dispatcher will call to schedule. No cost, no obligation.