Roof coatings
A coating is a service-life decision, not a way to avoid one
Coatings are oversold and genuinely useful, which is an awkward combination. On a structurally sound, dry roof with its details repaired first, a coating extends service life and drops the surface temperature. On a wet assembly it is paint over a problem, and the problem carries on underneath it.
What a coating actually does
- Seamless surface
- It cures into one continuous film across the field and up over flashings and curbs, so the laps and terminations that leak on an aging membrane are covered as one piece rather than patched individually.
- Reflectivity
- A white coating reflects a large share of the solar load. The membrane under it runs cooler, which slows how fast it ages, and less heat reaches the space below.
- Ultraviolet protection
- It takes the sun so the membrane beneath it stops doing so. On this coast that is the mechanism that matters most, because ultraviolet exposure is what is ending that roof.
- A warranty on a system, not a miracle
- Coating manufacturers warrant systems installed at a specified thickness over a prepared and approved substrate. The preparation and the thickness are the whole job, and they are what gets cut when a price is being beaten.
The chemistries, plainly
| Type | Where it suits | What to know |
|---|---|---|
| Silicone | Roofs that pond, and single-ply or modified bitumen in reasonable condition | Handles standing water better than the alternatives and holds reflectivity reasonably well. It holds dirt, and it is slippery when wet, which matters on a roof people walk |
| Acrylic | Sloped roofs that drain properly, and metal | Economical, recoatable and breathable. It is water-based, so it needs a dry window to cure and it erodes over time where water stands on it |
| Urethane | Roofs with real foot traffic, and as a tough base coat under a reflective top coat | The most impact and abrasion resistant of the three, and usually specified as part of a two-coat system rather than alone |
| Metal roof systems | Through-fastened metal roofs with fastener and seam leaks | Fasteners, seams and laps are treated individually with tape or detail coat first. The field coating is the last step, not the repair |
Which roofs are candidates
- The insulation under it is dry. This is the condition that decides everything else, and the only way to know is core cuts or a moisture survey. Coating over wet insulation traps it, and the deck below carries on corroding.
- The membrane is aged but sound, with its seams intact and its failures local rather than systemic.
- The details have been repaired first. Curbs, pitch pockets, drains, terminations and edge metal are repaired as roofing work before any coating is applied over them.
- It drains. Ponding rules out some chemistries entirely and shortens the life of the rest, and it is a drainage defect worth correcting rather than coating over.
- Somebody can recoat it later. The service-life argument for a coating depends on a maintenance recoat at the right time, which means it has to stay in the roof file.
A coating does not restart the clock on a roof. It extends the service life of an assembly that still has one, and the honest version of the conversation states how many years it is expected to buy, what has to happen at the end of them, and what it would cost in service life to skip the preparation.
How a coating job goes wrong
| What happened | Why it failed | What was needed |
|---|---|---|
| Applied over wet insulation | The moisture had nowhere to go and the deck kept corroding under a roof that looked new | Core cuts first, and a tear-off of the wet areas |
| Applied too thin | Coating systems are specified by cured thickness; under-application is invisible on the day and shows up as early failure | A stated mil thickness, and a way of verifying what went on |
| Substrate not cleaned or primed | Adhesion failed, and the coating released in sheets | Power washing, repairs, and the primer the system actually specifies |
| Details coated rather than repaired | The coating followed the defect and split at the same place | Roofing repairs first, detail coat and reinforcing fabric at every transition |
| Sold as a new roof | Expectations set for a replacement and met with a maintenance system | A written statement of what it is, what it does, and how long it is expected to do it |
The test question for any coating proposal is simple: ask what evidence there is that the insulation is dry. If the answer is not core cuts or a moisture scan, nobody knows, and a coating is a bet on the most expensive variable in the building.
Have an aging flat roof and want to know whether it is a coating candidate or a replacement?
Talk to us about the buildingIs a coating cheaper than a replacement?
It is a different kind of spend with a different service life, and this site does not publish figures for either. The useful framing is that a coating over a sound, dry roof defers a capital project and a coating over a wet one wastes the money and the years. Which of those you have is a survey question.
How long does a roof coating last?
It depends on the chemistry, the thickness actually applied, the substrate and whether the roof ponds. What is consistent is that the systems are designed to be recoated: a coating that is maintained and recoated on schedule is a strategy, and one that is applied and forgotten is a delay.
Will a coating stop my roof leaking?
Only if the leak is the aging surface itself. Leaks at curbs, drains, terminations and penetrations are repaired as roofing work first; a coating applied over an unrepaired detail fails at that detail. Anyone offering to spray a leak away has skipped the part that matters.
Does a white coating really reduce cooling costs?
A reflective surface lowers the roof temperature substantially in this sun, and some of that heat was reaching the space below. How much it is worth depends on the insulation under the membrane and what the building does; on a poorly insulated building over a Gulf Coast summer it is noticeable.
Can a coating go over any membrane?
No. Compatibility between the coating chemistry and the existing surface is a real constraint, and so is the condition of that surface. Establishing what is up there — system, age, layers and moisture — comes before anybody chooses a product.
All work is performed by insured local roofing professionals. Texas does not license roofing contractors at state level, so insurance, references and a written scope are what there is to check.