By Joevel Faustino, TopCo Roofing
Your flat roof is getting old. There’s a stain on a ceiling tile, the membrane looks chalky, and the replacement quotes on your desk run to five or six figures.
Then someone suggests a coating. Roll a liquid membrane over the roof you already have, skip the tear-off, and buy yourself another decade.
Sometimes that’s exactly the right call. Sometimes it’s money poured over a problem that keeps growing underneath.
The difference comes down to what’s happening inside the roof, not on top of it. Here’s how to tell which one you have before you sign anything.
Table of Contents
What a Roof Coating Actually Does
A roof coating is a liquid-applied layer, usually silicone, acrylic or polyurethane, that cures into a seamless skin over an existing low-slope roof.
It’s a restoration, not a new roof system. It renews the waterproofing surface. It doesn’t add insulation, doesn’t stiffen a sagging deck, and doesn’t dry out anything that’s already wet.
In a light color, it also reflects sun. The U.S. Environmental Protection Agency lists liquid-applied coatings in light or cool colors among its low-slope cool roof products, and notes that high reflectance and high thermal emittance together lower temperatures on the roof, inside the building and in the air around it.
The Numbers Behind the Decision
Cost is why coatings get a look at all.
TopCo Roofing, which coats and replaces commercial roofs across South Mississippi, prices a full replacement at $8 to $15 or more per square foot and a commercial roof coating at $2 to $4. On a 10,000-square-foot roof, that’s $80,000 to $150,000 against $20,000 to $40,000.
A properly applied system, in their experience, adds 10 to 15 years of service life. The work usually takes two to five days, with no tear-off.
That gap is real. But it only holds if the roof underneath is sound enough to coat. The next four checks tell you whether yours is.
Check 1: Is the Insulation Dry?
This is the question that decides everything.
Commercial roof failures tend to follow the same path. Minor membrane damage lets water in. The water saturates the insulation. Wet insulation leads to a deteriorating deck. Left long enough, the system fails.
A coating can stop that process at the first stage. It can’t undo the later ones.
That’s why wet insulation, along with structural damage and severe deterioration, takes a roof off the coating list. Wet areas have to be found and repaired before any coating goes down.
You won’t find them from the ground or from the top of a ladder. Before you accept a coating quote, ask for a moisture survey: readings taken across the roof with moisture detection equipment, with the wet areas marked on a plan and photographed.
If a contractor quotes a coating without one, you don’t know what you’re coating over.
Check 2: Where Does Water Sit After Rain?
Ponding is water still standing on the roof 48 hours or more after it stops raining.
Go up (or send someone) two days after a good rain. Note every spot that’s still wet, and roughly how big each one is.
Some ponding can be handled with the right product. Silicone is the usual choice for areas that hold water.
Severe ponding is a different problem. If whole sections hold water for days, the drainage needs to be improved before a coating goes on. A coating doesn’t change where water goes.
Check 3: How Bad Is the Membrane?
Scattered, repairable defects are normal on a roof that’s a good coating candidate. Widespread failure is not.
Walk the roof and look for:
- Splits, cracks, blisters and punctures in the membrane
- Seams pulling apart on TPO, PVC or EPDM roofs
- Flashing separating at walls, penetrations and rooftop equipment
- Damage around HVAC units and the paths technicians use to reach them
- Clogged drains, which cause ponding of their own
- Soft areas underfoot or visible sagging, which point to deck trouble
Count and photograph what you find. If the list is a handful of local repairs, you’re in coating territory. If the membrane is failing everywhere, or the deck is soft, you’re shopping for a replacement.
Check 4: Has the Roof Been Coated Before?
If your roof was coated by a previous owner or during an earlier repair, that changes the job.
A new coat can go over an old one only if the existing coating is still well adhered and in good condition. Ask how the contractor will check adhesion before relying on it, and make sure the answer is in the scope.
Matching the Coating to the Roof
There isn’t one right coating for every roof. Different products suit different areas:
- Silicone for areas that pond
- Acrylic for areas with slope that shed water
- Polyurethane for high-traffic zones, such as walkways to rooftop equipment
A roof with both ponding areas and busy service paths may need more than one. Your quote should say which product goes where.
If energy savings are part of the reason you’re coating, keep the surface clean. The EPA notes that low-slope cool roofs in particular may need periodic cleaning to hold their reflectance.
What a Good Coating Quote Should Spell Out
This is where good jobs and cheap jobs separate. Before you sign, make sure the quote covers:
- Power washing to remove dirt and biological growth
- Repairs to every damaged area, listed by location
- How ponding areas will be handled
- Confirmation the surface will be completely dry before application
- Primer, if the coating system calls for one
- The product and coating type for each area of the roof
- The dry film thickness, and how it will be measured and recorded
- The manufacturer warranty, which typically runs 10 to 20 years
Pay the most attention to thickness. Manufacturers typically specify a minimum dry film thickness of 20 to 30 mils, depending on the system, for the warranty to apply.
Some applicators go on at 10 to 15 mils to save material. Those jobs fail early, sometimes in two or three years, and can void the manufacturer’s warranty. When a coating fails that fast, the cause is usually the prep or the thickness, not coatings as a category.
Keep It on a Schedule
A coated roof still needs looking after.
Inspect it at least twice a year, in spring and fall. Most commercial roof failures develop over 12 to 24 months before anyone sees them from inside the building, so a scheduled inspection is how you catch the small repair before it becomes the big one.
The Bottom Line
A coating is a good deal on a roof that’s dry, drains properly and is mostly intact. It’s a poor one on a roof that’s wet underneath.
Get the moisture survey first. Then compare the coating quote against replacement, line by line.
About the author
Joevel Faustino works with TopCo Roofing, a Hattiesburg, Mississippi roofing contractor that repairs and replaces roofs for homeowners and businesses across South Mississippi.
