Bubbles, Pinholes and Fish Eyes on a New Silicone Roof Coating: Which Defects Are Cosmetic and Which One Points at the Roof

Most blemishes you will spot on a freshly coated silicone roof are cosmetic, and one of them is not. Fish eyes, pinholes and small craters are surface defects in the coating film itself: they come from contamination, trapped air or rain during application, and a compatible silicone patch fixes them in minutes. Blisters are different. A blister means moisture is trapped under the coating, and it is telling you something about the roof, not the paint job. Here is how to tell them apart on a walk-through, which ones your contractor owes you a repair on, and why a well-run job rarely produces any of them.

The four things you will see, and what each one means

A silicone roof coating goes down at roughly 20–30 dry mils across two coats, then cures by reacting with moisture in the air. Anything that interrupts that film while it is still wet leaves a mark. Industry guidance from the Roof Coatings Manufacturers Association breaks the marks into four types:

• Fish eyes — tiny unpopped bubbles, pencil-eraser size or smaller, with a shallow ring around them and a top so thin it looks clear. They are almost always contamination: oil, grease, residual cleaner, or a stray drop of a different silicone product on the substrate or in the spray rig. A crew that runs the wrong lubricant through its pump can seed fish eyes across a whole roof section.
• Pinholes — holes the width of a pin that go through one coat. Air whipped in during mixing, or air pockets in a textured substrate like granulated modified bitumen, escape as the film cures. They are mostly a thin-coat problem; a proper second coat covers nearly all of them, which is one reason single-coat “bargain” jobs fail early.
• Craters — small bowl-shaped dips, pencil-diameter or less. Either an early blister popped and cured open, or rain hit the coating before it was rain-safe and each drop pushed the wet material aside. The floor of a crater is very thin, so UV reaches the membrane below.
• Blisters — larger raised areas, thicker on top, sometimes soft when pressed. These are the ones to care about. The usual cause is coating applied over a wet or damp substrate. They may appear the same day or weeks later, when the first hot afternoon heats the trapped moisture and vapor pressure lifts the coating.

Blisters: the one defect that points at the roof, not the coating

Fish eyes, pinholes and craters are workmanship issues: annoying, fixable, and unrelated to whether the roof was a good coating candidate. A blister is evidence that water was present when the coating went on: dew or a shower the crew did not wait out, a wash-down that had not dried, or worst of all, insulation already saturated below the membrane.

That last case is why we insist on a moisture scan before any coating quote. An infrared or nuclear survey finds wet insulation the eye cannot see, and any area past roughly 25% wet is cut out and replaced before the first gallon opens; see why your silicone warranty depends on a moisture scan you will never see. A blister over a scanned, dried roof is a small isolated repair. A pattern of blisters over an unscanned roof can be a warranty denial, because the manufacturer’s inspector will read it as coating over wet insulation, which every silicone warranty excludes.

One thing blisters are not: proof that silicone was the wrong choice. Silicone tolerates ponding water for the life of the roof; it simply cannot go on a roof that is already wet underneath, and neither can anything else.

Cracking: mud cracks versus alligatoring

Surface cracking comes from the opposite mistake. Mud cracking, a network of fine splits like a dried puddle, happens when a coat goes on too thick in one pass and the surface skins over and shrinks faster than the material beneath it. It is why a certified crew checks wet mil thickness with a gauge every few minutes; see the five application mistakes that can void your warranty.

Alligatoring, the deep, scaly cracking that looks like reptile hide, is UV aging of an old asphalt roof or a worn acrylic coating. It is a reason to restore the roof, not a symptom of new silicone. If you see it today, that is the “before” photo.

How each defect is repaired, and who pays

The repair path is short, and on a legitimate job it is the contractor’s cost, not yours:

• Fish eyes and pinholes: solvent-wipe the area and brush on a spot coat of the same silicone, or a silicone sealant for a single hole. Twenty minutes for a typical cluster.
• Craters: the same spot recoat, brought back to specified thickness so the thin floor no longer exposes the membrane.
• Blisters: cut the blister out, probe the substrate for moisture, dry it or replace the wet insulation, then recoat with a fabric-reinforced silicone patch feathered into the field. The roof gets no weaker: fresh silicone bonds to cured silicone without primer.

Walk the roof with the crew at final inspection and again 30–60 days later, after a few hot days have had the chance to raise any blisters, and get anything you find onto the punch list before final payment. None of this shortens the coating’s life once corrected: a properly repaired roof carries the same 10–20 year manufacturer warranty, and the restoration still lands at $3–6 per square foot against $10–16 per square foot for a tear-off, a 50–70% saving done in 1–3 days instead of weeks. Our guide to how long a silicone roof coating lasts shows what the film should look like at year 10 and year 20.

The roof you should actually see after a coating job

The answer to “what should my new silicone roof look like?” is: boring. A uniform white field, slightly textured where granules were broadcast in the walkways, no shine differences between spray passes, and nothing that bubbles or gives underfoot. Fish eyes and pinholes mean a rushed crew or dirty equipment. Blisters mean a skipped moisture survey. Both are avoidable, and both are why the applicator matters as much as the product.

If you are weighing a coating for a flat or low-slope commercial roof, start with the numbers: run your square footage through our silicone roof coating savings calculator to see the coating-versus-replacement gap for your building. Warehouse and distribution owners can see what a large-roof project involves on our warehouse roof coating page, and Delaware owners can start on the Delaware silicone roof coating page. Then book a free commercial roof assessment. It includes the moisture scan, so the blister question is answered before anyone opens a pail, across Pennsylvania, New Jersey, Delaware, Maryland, Ohio and West Virginia.