# Fiberglass Damage Triage: Repair, Section or Replace > How to read composite damage on an RV shell and decide between gelcoat repair, laminate patching, core replacement and cap replacement. Source: https://ocrv.info/resources/guides/fiberglass-damage-triage Fiberglass damage triage is the process of classifying damage to an RV composite shell by depth and structural consequence, then matching each class to the correct fix: gelcoat repair, a laminate patch with a tapered scarf, core replacement and re-skin, or full molded cap replacement. Depth, not surface area, drives the decision. Composite damage lies about itself. A crack the width of a hair in a rear cap can sit above eight square feet of separated laminate, and a fist sized hole in a sidewall can be the entire extent of the problem. Triage exists to close the gap between what the eye reports and what the panel is actually doing. The estimating and structural departments at our Yorba Linda shop work through a fixed sequence of tests before anyone reaches for a grinder, because grinding into the wrong repair plan wastes material, hours and the owner's patience. Owners arriving from Eastvale usually come in after one of three events: a low speed contact with a post or a garage opening, a road debris strike at highway speed, or slow water intrusion that finally announced itself as a soft spot underfoot. Each leaves a different signature. Impact damage radiates outward from a point and tends to be sharply bounded. Debris strikes punch through and leave a star pattern with fiber blown outward on the back side. Water damage has no clean edge at all, and mapping its boundary is most of the work in the first hour. Nothing in this guide requires exotic tooling to begin. A coin, a bright work light held at a low angle, a pin type moisture meter and a straightedge will tell you most of what you need to know. What the shop adds is the ability to act on the finding: controlled removal, resin selection matched to the existing substrate, vacuum consolidation, and a refinish department that can carry gelcoat or paint back across the repaired area so the seam does not read from ten feet away in direct sun. ## Why a laminated sidewall and a molded cap are not the same repair Start with how the two parts were built. A modern RV sidewall is a sandwich panel. A thin outer skin, often a filon style fiberglass reinforced panel around 0.040 to 0.090 inch thick, is bonded to a lauan plywood facer. Behind that sits block foam or fiberglass batt insulation packed between aluminum tube or welded steel framing, and behind that a thin interior wall panel. The whole stack is pressed or roller laminated with urethane or contact adhesive and cured under pressure. Its stiffness comes almost entirely from the skin staying glued to the core, not from the thickness of any single layer. A front or rear cap is a different animal entirely. It was sprayed with gelcoat into a female tool, then built up with chopped strand from a chopper gun or with hand laid mat and resin, sometimes with balsa or foam coring across the roof span and plywood backers buried where the ladder, the awning arm or the marker lights attach. Thickness inside one cap can vary from 3/32 inch in an open field to over half an inch at a tight radius. There is no adhesive bond line to fail, so a cap fails by breaking fibers rather than by letting go. That difference decides the whole repair plan. Sidewall trouble is usually a bond failure, so the fix is about re-establishing adhesion across a mapped area rather than adding laminate strength. Cap trouble is usually a fiber failure, so the fix is about rebuilding laminate to a thickness and fiber orientation that carries load again. Finish adds a second split. Caps are typically gelcoat, which can be ground, filled and buffed as a single material. Painted filon sidewalls need a refinish path with primer, base and clear, plus a blend that reaches a natural break line. ## What are the damage classes, and how do you tell them apart? Six classes cover nearly everything that rolls through the door. Surface crazing is a fine web in the gelcoat only, usually from ultraviolet exposure and thermal cycling, and it does not reach the laminate. Stress cracking radiates from a fastener, a corner radius or a window cutout and signals flex the part was never designed to absorb. Gelcoat fracture goes through the finish and into the first ply. Delamination is a bond release with the skin still intact. Core crush is compressed foam or lauan under a skin that still looks acceptable. Through-penetration is a hole with damaged fiber across the full section. The tap test separates them faster than anything else. A quarter held on edge, or better a small plastic tipped tap hammer, worked across the panel in a two inch grid produces two very different sounds. Sound laminate over a bonded core returns a sharp, high tick that dies immediately. A released or crushed area returns a dull, hollow thud with a longer tail. That dead sound means the skin is no longer transmitting energy into the substrate behind it. Mark every dull hit with chalk as you go, because nobody remembers a pattern of forty hits accurately. Boundary finding is where people get lazy and where repairs come back. Always tap from known good material inward toward the suspect zone, then repeat the sweep from four directions, because the transition point often lands a full inch apart depending on the approach. Cross-check with a pin type moisture meter at the lowest chalk line, since water tracks down and pools at the bottom of a released area. Finish by standing at a shallow angle with a work light and looking for the slight bulge or oil-canning that betrays a released skin carrying load it cannot share. - Surface crazing: sand, fill with gelcoat or refinish, no structural work required - Stress cracking: relieve the source of flex first, then repair, or the crack returns in a season - Gelcoat fracture: grind to sound laminate, replace one or two plies, refinish - Delamination: map the boundary, then inject resin or open the skin and re-bond - Core crush: the skin comes off, the crushed material comes out, new core goes in - Through-penetration: tapered scarf, full laminate rebuild, fair and finish ## Which resin and which reinforcement belong in the repair? Resin choice is a bonding question before it is a strength question. Orthophthalic and isophthalic polyester is what most RV caps were built from. It bonds beautifully to itself while still green, meaning within the same working session, and poorly to anything fully cured. Vinyl ester sits in the middle with better toughness, better water resistance and a real improvement in secondary adhesion. Epoxy has the best secondary bond of the three, sticks to cured polyester, to wood and to metal, and shrinks the least during cure. The trap is the reverse direction. Polyester and gelcoat do not bond reliably over cured epoxy. That single fact drives the sequencing of every job. If a cap is going to be finished in gelcoat, the structural laminate should stay in the polyester or vinyl ester family so the gelcoat has something it actually wants to grip. If the repair is going to be primed and painted instead, epoxy becomes attractive because it holds onto the old cured laminate far better. Reinforcement follows the same kind of logic. Chopped strand mat is held together with a styrene soluble binder, so it wets out properly in polyester and fights back against epoxy unless the mat was made without that binder. For the actual stack, biaxial stitched cloth does most of the useful work. It drapes into a radius without bridging, puts fiber in two deliberate directions instead of relying on random orientation, and prints through less than woven roving. Woven roving still earns a place where a flat area needs bulk and stiffness in a hurry, but it leaves a weave pattern that has to be filled and faired. Finish the outside with a light surfacing veil so the fairing stage removes material from a sacrificial layer rather than cutting into the structural plies underneath. - Polyester: matches most original cap laminate, accepts gelcoat, weak secondary bond to cured surfaces - Vinyl ester: better toughness and moisture resistance, still friendly to a gelcoat finish - Epoxy: strongest secondary adhesion and lowest shrink, but do not lay gelcoat over it - Chopped strand mat: polyester only, unless the binder is specified as epoxy compatible - Biaxial stitched cloth: best drape and directional strength for a structural patch - Surfacing veil: a sacrificial outer layer that keeps the fairing block off your structure ## How is a structural patch actually laid up? A butt joint in composite is a hinge waiting to happen. Load has to transfer through shear area, so the repair gets a tapered scarf instead. The working ratio is twelve to one: for laminate 1/4 inch thick, the taper extends three inches back from the hole edge on every side. Lay that out with a compass and a marker before touching a sander, because it is easy to under-taper and impossible to add material back once it is gone. Grind with 36 grit on a soft interface pad, keep the taper even, and stop when the ply layers show as clean concentric rings. Wipe the scarf with acetone, let it flash off, and lay up from the smallest patch outward so each successive ply overlaps the one below it by roughly one taper step. That order puts the largest ply on the outside where it locks the whole stack down against peel. Wet out on a clean board rather than on the part so you control resin content instead of flooding the repair. Peel ply over the top leaves a ready to bond texture without sanding. If the panel has a core, pull vacuum at partial pressure, around eight to twelve inches of mercury, because full vacuum crushes light foam. Delamination without a hole is a different procedure altogether. Drill 1/8 inch injection ports on a three to four inch grid inside the chalked boundary, vacuum the cavity clean, and push low viscosity epoxy or a two part panel bond adhesive through each port until it appears at the neighboring hole. Then clamp. Cauls made from plywood faced with closed cell foam spread the pressure without printing hard spots into the skin. Warm the area gently to lower viscosity before injection, not after. Cosmetic repairs skip this entire step, which is exactly why they lift again the following summer. ## When does replacing the cap cost less than saving it? Hours settle the argument before opinions do. Surface crazing on a panel typically lands in a two to four hour band. A gelcoat fracture with one or two damaged plies runs four to eight. A properly scarfed laminate patch under one square foot runs eight to sixteen. A mapped delamination runs twelve to forty depending on area and on whether the skin has to come off. Through-penetration with core replacement and refinish runs twenty to sixty. At the posted body and paint rate of $210 per hour, plus paint supplies at $55 per paint hour and body supplies at $5 per body hour, those bands separate very quickly. Cap replacement changes the arithmetic in a way that surprises people. A molded cap is a special order item, which means a 100 percent non refundable deposit at the time of ordering, and it arrives crated on a freight truck with a lead time that usually places the job in the extended tier of four to ten weeks. The labor, though, is bounded and predictable: cut the old cap loose, address the flange and attachment points, set and bond the new part, seal every penetration, then refinish. Twenty five predictable hours against sixty uncertain ones is a real argument. The honest recommendation tips toward replacement under a few specific conditions. Damage crossing more than two structural attachment points is one. A cap that has already been repaired twice in the same region is another, because each repair changes local stiffness and pushes the next crack somewhere new. Distortion in the molded shape, where the part no longer matches the profile of the roof or the sidewall it meets, is the clearest signal of all. Collision estimates at our shop are complimentary, and RV systems estimates run $150, credited back against an authorized repair. - Two to four hours: gelcoat crazing, sand, fill and buff - Four to eight hours: gelcoat fracture into the first plies - Eight to sixteen hours: scarfed laminate patch under one square foot - Twelve to forty hours: mapped delamination, injected or opened and re-bonded - Twenty to sixty hours: through-penetration with core replacement and refinish - Replacement triggers: damage across multiple attachment points, a twice repaired region, or a cap that no longer matches its mating profile ## Frequently asked questions ### Can I fill a spider cracked area with body filler and paint over it? You can, and it will look correct for a few months. Polyester filler is not flexible and it is not waterproof at the edges. If the crazing came from ultraviolet exposure and thermal cycling, the same movement continues underneath the filler and telegraphs a new crack pattern through the paint. If the crazing came from flex around a fastener or a corner, the filler adds a stiff island that concentrates stress at its perimeter. Grinding the gelcoat back to sound material and rebuilding in a compatible resin is the repair that holds. ### How do I know whether the wall behind a delaminated skin is wet? A pin type moisture meter read at the lowest point of the chalked boundary tells you more than a reading in the middle, because water migrates down and collects at the bottom edge of a released area. Compare against a reading taken on the same wall four feet away in known good material. A difference of several points, a musty odor at the nearest interior seam, or a stain line on the lauan when a small inspection cut is made all confirm it. Wet lauan has to come out, not dry in place. ### Will a repaired gelcoat area ever match the rest of the coach? Aged gelcoat has oxidized, chalked and shifted color for years, so a fresh mix of the original formula will never match straight from the can. The refinish department tints to the panel as it exists today rather than to the factory code, sprays a test card, and checks it in direct sun rather than under shop lighting. On a panel with a natural break line the blend disappears. On a large flat side with no break, the honest answer is that the panel gets finished corner to corner so there is no transition to see. ### Is a soft floor the same problem as a delaminated sidewall? They share a cause and not much else. Both usually start as water intrusion through a failed seal, but a floor is a horizontal structural panel carrying live load, while a sidewall skin is a stressed membrane. A soft floor means the plywood core has lost compressive strength and it must be cut out and replaced, often with the furniture and sometimes the slide out removed for access. A delaminated sidewall can frequently be re-bonded through injection ports without opening the interior at all. ### How long will fiberglass work keep my coach in the shop? It depends on which tier the scope falls into. A gelcoat fracture repair usually fits the short tier of three to eight days. A scarfed patch with refinish typically lands in the standard tier of two to four weeks, because resin cure, fairing, primer and clear each need their own time and none of it can be rushed without a visible result. Delamination work with core replacement, or a molded cap replacement with freight lead time, runs into the extended tier of four to ten weeks. --- OCRV Center. 23281 La Palma Ave, Yorba Linda, CA 92887. (949) 799-3387. info@ocrvcenter.com. Serving Eastvale, California in Riverside County, about 20 miles from the shop. All work is performed in shop at the Yorba Linda facility. No mobile, roadside or on-site service is offered. Scope is body, paint, structural, fiberglass, interior and vehicle systems work. Engine rebuilds, transmission rebuilds, drivetrain work, DOT inspections and emission testing are not performed.