A Crack in Fiberglass Is a Symptom With an Address

Look at the shape and where it starts. An impact crack radiates outward from a single point, often with a star or spider pattern, and there is usually a visible strike mark, a scuff or a dent at the centre. It stops when it runs out of energy.

A stress crack starts at a corner and runs. It begins at the corner of a window opening, a door frame, a slide opening, a compartment hatch or a mounting point for a ladder, an awning rail or a marker light. There is no strike mark. The crack is telling you that the panel is flexing more at that corner than the gelcoat can follow, which happens because the structure around the opening is moving.

The practical difference is what has to be done. An impact crack is repaired and it is finished. A stress crack repaired without addressing the flex reopens, usually within a season and usually within an inch of where it was. That means checking the opening for square, checking the frame or subframe behind it, and looking at whether a slide, a jack or a mounting point is loading the corner.

Punctures are simpler. A branch, a ladder, a gate post or a dock corner goes through the skin, and the question is only how much substrate went with it.

Fiberglass repair is not filling a hole. It is rebuilding the laminate so the finished panel has the same thickness and strength it had before.

1. Stop drill. A small hole at each crack tip removes the stress concentration so the crack cannot extend while the panel is worked.
2. Bevel and feather. The edges are ground to a long taper, roughly twelve times the panel thickness on each side, giving the new laminate a wide bonding surface. Butting a patch against a square edge is the single most common reason a home repair fails.
3. Backing. On a through hole, a backing layer goes in from behind where access allows, or a temporary form is used where it does not.
4. Layup. Glass is laid in successive plies, smallest first on the back side and progressively larger toward the surface, each wetted out fully and allowed to cure.
5. Fair and finish. Polyester filler over the cured laminate, blocked flat, primed, blocked again, sealed, then refinished with the colour blended into adjacent panels.

Body labor is $210 per hour with body supplies at $5 per body hour and paint supplies at $55 per paint hour. On a small repair the finishing stages carry more hours than the structural ones, which is normal on a curved panel where the shape has to come back exactly.

Curvature is the first driver. A crack on a flat sidewall is blocked flat with a straight board and the eye accepts the result. A crack across the compound curve of a front cap has to be faired to a shape that changes in two directions at once, and there is no board that does that for you.

Position is the second. A repair mid panel can be blended and disappears. A repair that crosses a body line, a seam, a rub rail or a graphic has to end up matching on both sides of that feature.

Access is the third. Punctures near a window frame, a compartment box or a slide opening may need the adjacent component removed to get a backing layer in, and that removal and reinstallation is often more time than the layup.

Finish is the fourth and the largest. A solid white cap is a fast refinish. A three stage pearl, a multi colour scheme or a decal crossing the repair pushes into spot repair and blend matching or into graphics recreation, and that is where a $900 repair becomes a $4,000 one.

Two things matter immediately, and they are both about keeping water out.

• Cover it. Tape and plastic over a through hole is not a repair but it stops water reaching the substrate. Wet luan is what turns a $900 patch into a substrate replacement.
• Do not seal it with silicone. Silicone contaminates the surface for a long distance around, and every trace of it has to be removed before any resin, filler or paint will bond. It reliably adds hours to the repair.
• Photograph it dry. Straight on and at a shallow angle, with something for scale.
• Check inside. Look at the interior wall behind the damage for staining, softness or a popped seam.
• Note the cause. If nothing hit it, that is important information, not a mystery to skip past.

Related work sits at RV and camper fiberglass repair for general laminate work and delamination repair where the surrounding area sounds hollow. Bands are on the price sheet.