Thermal Checking Repair

Q: How long does a thermal checking repair take?

It is a multi-stage fiberglass and paint job with cure time between stages. Full sidewall repairs are measured in weeks, not days. A schedule is provided with the estimate.

Q: Will thermal checking come back after the repair?

A proper fiberglass repair removes the cracked laminate so the wall starts fresh. Lightening the darkest colors, keeping the coach waxed, and shading the sun side reduce recurrence. Repairs carry a 5-year thermal checking warranty with an annual wax and inspection.

Fiberglass repair

Thermal checking repair for dark-color motorhomes and coaches

A web of fine cracks spreading across a dark fiberglass sidewall is thermal checking. It is not a paint failure — the fiberglass laminate itself has cracked from years of heat cycling in the sun. We repair the fiberglass first, then repaint, so the cracks don't come back through the new finish.

Why it happens

Dark paint absorbs far more solar heat than light paint. A dark sidewall runs much hotter than the air on a summer afternoon, then cools completely overnight. Every cycle makes the fiberglass expand and contract against the framing and backer it's bonded to. Over thousands of cycles the resin fatigues and cracks — always worst on the sunny side and on the darkest sections of the scheme.

Why paint alone doesn't fix it

Filling the cracks and repainting covers the symptom. The fractured laminate is still underneath, and the first hot season moves it again — the same pattern telegraphs through the new paint, usually within months. If a thermal checking estimate is essentially a repaint, expect to do it twice.

How we spot it vs. other problems

Thermal checking: fine branching cracks, worse on dark colors and the sun side.
Delamination: soft spots, bubbles, skin lifting from the wall — a different substrate repair.
Clear coat failure: dull, chalky or peeling finish with no cracks in the fiberglass — that one is a paint job.
Stress cracks: single long cracks at seams, windows or corners — check the framing.

Close-up of thermal checking: fine web of cracks in a dark blue fiberglass motorhome sidewall — What thermal checking looks like up close — cracking in the fiberglass under a dark color.

Dark-color diesel pusher motorhome in the shop for fiberglass thermal checking repair on both sidewalls — Diesel pusher in for thermal checking on both sidewalls — full wall repair, then repaint with painted graphics.

Our repair process

Grind the wall back to sound fiberglass — the cracked laminate is removed, not filled.
Lay new fiberglass to rebuild a continuous, uncracked skin.
Fair and block the wall straight so the repair disappears in the finish.
Prime, seal and repaint, including painted graphics if the coach has them.

Checking is rarely isolated, so we usually repair the whole wall. Plan on weeks in the shop, not days.

Keeping it from coming back

Lighten the darkest sections when you repaint — the most effective single change.
Keep it waxed or sealed. A protected surface runs cooler and sheds UV.
Shade the sun side — covered storage or orientation adds years.

Our thermal checking repairs carry a 5-year thermal checking warranty, maintained through an annual wax-and-inspection visit.

Not sure what you're looking at? Send a photo.

Text pictures of the cracking and we'll tell you whether it's thermal checking, delamination or a paint issue — and what the repair looks like. Free estimates. Chino, CA — serving the Inland Empire, Los Angeles, Orange County and San Diego County.

Text photos to (909) 287-5280 Call (562) 254-0721

Thermal checking questions

What is thermal checking on an RV?

Thermal checking is a pattern of fine, branching cracks in a fiberglass sidewall caused by repeated heat expansion and contraction. It is most common on dark-colored motorhomes and coaches and shows up first on the side that gets the most sun.

Can thermal checking be fixed by repainting?

No. The cracks are in the fiberglass laminate, not the paint. Filling and repainting hides them briefly, but the cracking telegraphs back through the new finish once the wall heats up again. The laminate has to be ground back and re-glassed first.

Why do dark-colored RVs get thermal checking?

Dark paint absorbs much more solar heat, so the fiberglass cycles through a wider temperature range every day. Over years, that fatigue cracks the resin in the laminate. Lighter sections of the same wall are usually unaffected.

How long does a thermal checking repair take?

It is a multi-stage fiberglass and paint job — grinding, re-glassing, fairing, priming and repainting — with cure time between stages. Full sidewall repairs are measured in weeks, not days. We'll give you a schedule with the estimate.

Will it come back after the repair?

A proper fiberglass repair removes the cracked laminate, so the repaired wall starts fresh. Lightening the darkest colors, keeping the coach waxed, and shading the sun side all reduce the chance of recurrence, and our repairs carry a 5-year thermal checking warranty with an annual wax and inspection.