Fiberglass Repair for West Covina Owners

How RV fiberglass is actually built

Fiberglass on an RV is not one material, it is a stack. On a molded cap you typically have gelcoat sprayed into the mold first, then chopped strand and woven glass laid into resin, sometimes with a core material in flat areas for stiffness. On a laminated sidewall you have a thin filon or fiberglass skin, then adhesive, then a foam or azdel core, aluminum framing at the studs, and an interior panel, all bonded under vacuum into a single structural sandwich.

That difference matters for repair. A molded cap has real laminate thickness and can be ground, rebuilt and refinished almost anywhere on the part. A laminated sidewall skin is often thinner than a business card is thick, and its strength comes from the bond to the core rather than from the glass itself. You can repair a hole in it, but if the bond around the hole has failed, patching the hole alone accomplishes nothing.

Gelcoat is the third layer to understand. It is a pigmented resin surface, not paint, and it is typically a fraction of a millimeter thick. Many newer coaches are painted over the gelcoat instead, which changes the repair entirely: a painted cap is refinished with automotive materials, while a gelcoat cap can be repaired with color matched gelcoat and buffed rather than sprayed.

• Molded cap: gelcoat over structural laminate, repairable across most of the part
• Laminated sidewall: thin skin bonded to core and framing, strength comes from the bond
• Filon: a thin fiberglass reinforced panel used as a sidewall skin on many units
• Azdel: a composite core substrate used in place of luan on better built walls
• Luan: thin plywood substrate that swells and delaminates once it gets wet
• Gelcoat: pigmented resin surface layer, repaired and buffed rather than sprayed

Gelcoat cracks, stress cracks and spider webbing

Not every crack means damage underneath. Gelcoat is harder and more brittle than the laminate below it, and it cracks under flex that the structure absorbs without trouble. Fine cracking around a screw hole, at a tight radius or where a bumper mounts is usually gelcoat only, and it can be ground out and refilled without touching the glass.

Stress cracks tell a different story. When cracks radiate from a single point in a star pattern, something struck that point. When they run in a straight line for a distance, something below is flexing along that line, usually a structural joint or a support that has come loose. Repairing the crack without finding the flex source means it will return, generally within a season of Southern California temperature cycling.

The diagnostic step is straightforward. Cracks get ground open to see whether they stop in the gelcoat or continue into the laminate. A gelcoat only crack has a clean white laminate under it. A structural crack shows fractured fibers, and often a slight step where the two sides of the crack no longer sit flush. That second condition means the repair has to rebuild the laminate, not just the surface.

Age plays into it as well. Gelcoat becomes more brittle every year it sits in Southern California sun, so a coach that flexed the same way for a decade without complaint will start crazing once the surface layer has lost its flexibility. Fine crazing spread evenly across a whole panel is usually that, and it points toward a restoration or a refinish decision rather than a structural one. Cracks concentrated in a few specific places point the other direction.

Delamination: what a soft spot really means

Delamination is bond failure between the skin and the core. It presents as a soft area, a hollow sound when tapped, a visible bubble or a wave in the sidewall that shows up in low sun and grows on hot afternoons as trapped air expands. Owners often describe it as the wall having a bump that comes and goes, and that description is accurate.

The cause is almost always water. A leak at a window frame, an awning rail, a slide flange or a marker light lets water into the wall, where it sits between the skin and the core. On walls built over luan the plywood swells and turns to pulp. On azdel walls the substrate survives but the adhesive bond does not. Either way the panel loses the stiffness it was designed to have and starts flexing as a loose skin.

Heat drives the visible progression. A wall that is delaminated but not obviously bubbled in February will bubble in July, because the trapped moisture turns to vapor and pushes the skin outward. That is why so many delamination jobs arrive between June and September. The damage did not start then. It just became impossible to ignore.

Patching a hole versus replacing a panel

Repairing a hole in fiberglass properly means removing far more material than the hole itself. The damaged area is ground back to sound laminate with a long taper, typically twelve to one or better, so the new glass has enough bonded area to carry load across the repair. A patch cut to the size of the hole and bonded flat has almost no strength and will telegraph a ring through the finish.

Backing matters as much as the patch. Where the reverse side can be reached, the repair is laminated from behind first, which gives a clean face and a strong joint. Where it cannot, a temporary backer is bonded in place through the opening, the laminate is built up in layers from the front, and the surface is filled and faired only after the structure is restored.

Replacement takes over when the damaged area is too large to taper into, when the panel is thin skin over failed core across a wide area, or when the part is a molded cap that has cracked through its structure. On a laminated sidewall a section of skin can be replaced between features, though the seam has to be planned so it falls at a natural break rather than in the middle of a blank wall where it will always be visible under raking light.

Color matching gelcoat and painted fiberglass

Matching gelcoat is a different craft from matching paint. Gelcoat is tinted, applied thick, then sanded and buffed to a finish rather than sprayed to a gloss. Matching an aged gelcoat means tinting against the actual panel in daylight and accepting that the surrounding area may need polishing to bring it back toward the repair rather than the other way around.

Painted fiberglass follows the automotive process: prep, sealer chosen for the substrate, base to a matched sprayout card, then clear, with a blend into the adjacent surface. Fiberglass introduces one extra concern, which is porosity. A repaired laminate that has not been sealed properly absorbs solvent unevenly and produces dieback, where the gloss drops in the repaired area days after the vehicle looked perfect.

The other consideration is heat. A dark painted cap in the Southern California sun runs hot, and a repair that was not fully cured before finish will show print through as the resin continues to shrink. That is why cure schedules on structural laminate repairs are not compressed regardless of how tight the calendar looks. Waiting is part of the process.

Fiberglass on campers, truck bodies and slide faces

The same materials show up well beyond motorhome caps. Truck campers use molded fiberglass shells that crack at the corners where they load against the bed rails. Slide out faces are often laminated panels with a fiberglass skin, and they delaminate as readily as sidewalls do, usually starting at the top where the topper drains onto the face.

Commercial bodies use composites too. Reefer bodies and insulated boxes are fiberglass skins over foam core, and their failure modes are identical to an RV sidewall: impact damage that breaks the skin, then water intrusion, then a growing delaminated area. Repair follows the same logic of tapering back to sound material and restoring the bond across the whole repair area.

Food trucks and mobile business builds are the third category we see regularly. Those bodies take constant service door contact, equipment loads and pressure washing, and their fiberglass panels tend to crack at fastener locations. Restoring those areas properly usually means adding a backing plate or spreading the load rather than repeating the original fastening pattern that caused the crack.

Keeping the next fiberglass failure from happening

Almost every delamination job starts with a seal that was neglected. The prevention list is short and boring, and it works. Inspect every roof to wall seam, window frame, awning rail, slide flange and marker light annually, and reseal anything where the bead has shrunk, cracked or pulled away. Dicor and Eternabond products handle most of that work, matched to the substrate.

The second item is dealing with small breaches immediately. A cracked gelcoat area that has opened to the laminate will wick water along the fibers, and it does not need much of an opening to do it. Sealing that crack the week it appears is a small job. Repairing the delaminated area it produces two years later is not.

The third is sun management. Ultraviolet exposure is what turns gelcoat chalky and brittle, and brittle gelcoat cracks under flex it used to absorb. Covered storage, or an annual polish and protectant on a coach that lives outdoors, meaningfully extends how long the finish stays serviceable. West Covina summers are hard on an RV parked on a driveway all year.