You Cannot Coat a Wet Roof. Full Stop.

Roof Riffs is presented by Division 7 Sales, Inc. — independent Karnak manufacturers representative since 1990. Visit division7sales.com or subscribe to the Roof Riffs newsletter for industry insights delivered straight to your inbox.

Q: What happens when you apply roof coating over a wet roof?
A: Coating over a wet roof causes the system to fail. Moisture trapped in the insulation prevents proper adhesion, causing the coating to peel, blister, or delaminate. No liquid-applied coating system can perform as intended over saturated insulation. A moisture survey — infrared, nuclear, or core sampling — must be conducted before any roof restoration project begins. Wet areas must be cut out and replaced before coating.

John McDermott has been in the commercial roofing industry since 1987. In that time, he’s seen projects at every stage — from stack to finished surface to warranty claim. And when we asked him to pull from the vault and share the worst coating failures he’s ever encountered, the first story out of the gate involved a gymnasium.

The owner called. The coating system was coming off in sheets. The manufacturer who applied it wasn’t returning calls. Would John come take a look?

He did. And when he got there, he looked up at the underside of the gymnasium ceiling and saw everything he needed to know: wet insulation, destroyed ceiling tiles, moisture damage running through the whole system. Long before anyone applied a coating, this roof had been leaking. Nobody had done a moisture survey. Nobody had assessed whether the roof was in restorable condition. They just coated it.

It failed. Of course it failed.

The most important question in roof restoration

Before any coating system goes on a commercial roof, one question has to be answered: is this roof in restorable condition?

That’s not a visual assessment. You cannot look at a low-slope roof and know whether the insulation beneath it is wet. You have to conduct a moisture survey — whether that’s infrared, nuclear, or core sampling. If moisture is present in the insulation, no coating system will adhere and perform as intended. The wet areas have to be cut out and replaced before any restoration work begins.

John puts it plainly: “We can’t put anything over a wet roof. Selecting the roof that’s actually in restorable condition is so important.”

The contractor who said it was “liquid TPO”

Danny Bryson, founder of Division 7 Sales and an independent Karnak rep since 1990, added another one from his own experience. He was called to walk a roof that was, in his words, not a contestant for a coating at all. Someone had nailed ice and water shield to the deck — without even pulling the release liner off the back — and that was the roofing membrane. A contractor had come before him and proposed silicone coating, telling the building owner it was essentially liquid TPO with a 50-year leak-free warranty.

Danny’s response: “I couldn’t get off the roof fast enough.”

They reroofed it with metal a year later.

The desire to get the order

This is where Danny lands on the systemic issue: “The biggest thing I see is roofing salespeople whose desire to get the order is greater than their desire to do it right.”

Sometimes that means not understanding what they’re getting into. Sometimes it means knowingly moving forward on a job that shouldn’t be coated because the sale is there. Either way, the result is the same — a failed project, an angry building owner, and a warranty claim that goes nowhere because the underlying condition was never restorable to begin with.

The most valuable skill in roof restoration, John and Danny both agree, is knowing when to say no.

Division 7 Sales has represented Karnak Liquid Applied Roofing Solutions since 1990. If you’re evaluating a roof for a restoration coating and want a second set of eyes before you commit, reach out at division7sales.com. We’d rather help you walk away from the wrong job than watch you inherit a warranty claim.

Listen to the full conversation on Episode 1 of Roof Riffs, here or wherever you get your podcasts.

What are the most common commercial roof coating failures?  The most common preventable failures in commercial roof restoration are:
(1) coating over a wet roof without a moisture survey,
(2) inadequate surface cleaning before application,
(3) using expired coating material,
(4) choosing a system based on warranty rather than performance, and
(5) using the wrong equipment for the job.
According to John McDermott, VP of Sales at Karnak Liquid Applied Roofing Solutions, 100% of these failure modes are preventable.