Gelcoat Crack and Puncture Repair After an Impact
Written by Refinish Department Lead, Paint and Refinish Lead, OCRV Center. Reviewed by Structural Repair Lead
In shortA crack is a break in the laminate, not a scratch in the paint. It gets drilled at the ends, ground to a taper and rebuilt in layers. Most jobs land $600 to $5,500.
How is a crack or hole in RV fiberglass repaired?
Crack and puncture repair rebuilds broken laminate rather than covering it. We drill the crack ends to stop propagation, grind a long taper into sound material, lay in mat and woven roving, then gelcoat or refinish. Rancho Santa Margarita owners bring most of this work to our Yorba Linda shop after debris strikes.
- Drilling the crack tip is what stops it from running further
- Filler over a live crack always telegraphs back through within a season
- A repeating stress crack means something behind the panel is moving
- Punctures need backing support before any layup goes on the front
- Price range
- $600 to $5,5003 to 26 labor hours at $210 per hour
- Labor rate
- $210 per hourBody and paint department
- Typical turnaround
- 3 to 8 shop daysEach layup stage has to cure before the next one goes on
- Written estimate
- $150Credited in full against an authorized repair
- Common source
- SR-241 and 91 debris strikes, low branch contact off canyon roads, backing impacts in storage
Last verified
Something came off a truck ahead of you on the 241, you heard it hit, and there is now a white star about the size of a playing card on the front cap with four legs running out of it. Or a branch on a canyon road put a two inch hole through a compartment door. Either way the panel is broken, and broken laminate does not heal, settle down or stay the size it currently is.
This page is about localized structural damage: cracks, punctures and impact breaks in an otherwise healthy panel. It is not about a skin that has come unglued from its backing, which is a different failure with a different fix, and it is not about a whole panel being past saving. The work here is removing every fractured fiber and putting real glass and resin back in its place.
Reading a crack before anyone touches it
The first question is depth. A gelcoat only crack stops in the surface coat and does not reach the glass. A structural crack goes through into the laminate, and once fibers are broken the panel has lost strength there. Held under a light at a very low angle, the two look different: a surface craze scatters, a structural crack shows a defined dark line with a visible end point.
The second question is whether it is still moving. We measure a crack, mark both tips with a pencil and check it against any photographs the owner has. A crack that has grown since a storage lot photo from spring is active, and active cracks get treated more aggressively than dormant ones because the repair has to outlive whatever is driving it.
Impact cracks compared with stress cracks
An impact crack has an origin you can point at. Legs radiate from a single strike point, the pattern is roughly symmetrical, and there is often a small area of crushed gelcoat at the center. These are straightforward, in the sense that once you remove the broken material and rebuild it, the cause is in the past and it is not coming back.
A stress crack has no such center. It typically starts at a corner, a fastener or a change in panel thickness and it runs in one direction. The panel is being flexed by something: a bracket with no backing, a square cut opening that was never radiused, a slide rail bolted through skin, or a frame that has taken a hit somewhere else. Repairing the laminate without addressing that flex produces a repair that fails in the same place, which is the single most common repeat visit in fiberglass work.
- Impact crack: single origin, radiating legs, cause is historical
- Stress crack: starts at a corner or fastener, runs one direction, cause is ongoing
- A crack that returns after a good repair is always a stress crack
- Radiusing a square opening corner is often the actual fix
Drill stop, taper and layup schedule
The stop hole is the least impressive and most important step on this page. Drilling a small hole exactly at the tip of a crack converts a sharp stress riser into a round one, which is the difference between a fracture that keeps running and one that stops. Skip it and the crack frequently extends during grinding, which turns a one hour scarf into a three hour one.
Layup schedule then depends on what the panel needs to do. Mat conforms well and wets out easily, so it goes against the scarf first. Woven roving carries tensile load and goes on top. Where a crack has been recurring, stitched biaxial fabric is oriented deliberately across the crack line so the strength is added in the direction the panel was failing.
- Locate both true crack tips with a low angle light or dye
- Drill a stop hole at each tip
- Grind the full crack length open on a long shallow taper
- Wipe with solvent, dry under heat if any moisture is present
- Lay mat first, then roving or biaxial, rolling each layer out
- Cure fully, then fair, prime and finish
Punctures, through holes and backing support
A hole is a different problem from a crack because there is nothing left to lay up against. Something has to support the back of the repair, and what that something is depends on access. When the inside face is reachable, the layup is built from behind and the front only needs fairing. That is by far the better repair and it is why we ask about interior access before quoting a puncture.
With no rear access, a backing plate goes in through the hole itself, gets bonded or wired against the inside face, and the layup is built onto it from the front. It is a legitimate method used throughout the marine trade. What is not legitimate is packing a hole with filler and sanding it flush, which produces something that looks correct and carries no load at all.
Gelcoat finish compared with a painted refinish
If the surrounding surface is original gelcoat, patch gelcoat is usually the right finish. It is the same chemistry, it can be tinted to the panel, and it is thick enough to be cut and polished into the existing surface. Gelcoat needs surfacing wax added so it cures hard in open air, and it wants a warm bay, which in practice means the repair gets scheduled for a day when the shop is not opening bay doors every ten minutes.
If the unit is painted, or if the gelcoat around the repair is already too far gone to polish into, the repair gets sealed, based and cleared instead. That decision belongs to the paint side of the shop and it changes the estimate, because a painted finish has to be carried out to a break in the body rather than stopped at the edge of the patch.
What crack and puncture repair costs
This work bills at the body and paint rate. The number is driven far more by the finish than by the laminate. Rebuilding a two inch crack is a couple of hours of glass work. Making the repaired area invisible on a metallic painted sidewall can be four times that, because the refinish has to travel to a molding or a body line and the color has to be matched to a panel that has been in the sun for a decade.
Parts carry standard markup, sales tax applies to parts and materials, and labor is not taxed. Body and paint supplies are billed per hour of body and paint time, and a disposal charge applies because catalyzed resin is involved on every job of this type. A written estimate is $150, it documents the mapped fracture boundary, and it is credited in full against an authorized repair.
On cost
Ask what the refinish plan is, not just the repair plan. Two shops quoting the same crack can be a thousand dollars apart purely on how far the paint is carried, and the cheaper one is usually the one that stops at the patch.
Units that come in with impact damage most often
Anything with a large flat forward facing surface collects debris. Class A front caps take the worst of it because they are tall, vertical and the first thing to meet whatever came off the truck ahead. Class C units get hit on the cab over section, which is also the hardest area on the unit to reach from behind. Toy haulers pick up damage around ramp door openings, where the corners are square and already prone to cracking.
Working vehicles have their own pattern. A food truck collects impact damage at serving window corners and at the rear where equipment gets loaded and unloaded several times a week. Those units are usually on a schedule that will not tolerate a two week repair, so the layup sequence gets planned around service days and the unit goes back out between cure stages where that is practical.
Insurance on a road debris strike
A debris strike is normally a comprehensive claim rather than a collision claim, which usually means a different deductible and no at fault determination. Owners regularly pay out of pocket for damage that would have been covered because they assumed any road incident goes under collision. It is worth asking the carrier which coverage applies before deciding whether to file at all.
Documentation is straightforward on impact damage as long as it happens early. Photograph the panel the day it happens, note the road and the direction of travel, and keep any debris if it stayed with the unit. Where this gets difficult is a crack reported six months later, because by then the crack has grown and the carrier has a reasonable question about how much of it is from the reported event.
On the claim
Photograph a crack with a tape measure beside it on the day you find it. A dated image showing a four inch crack is what makes the eleven inch crack we grind out three months later provable rather than arguable.
What is included
- Crack tip location and stop drilling
- The true end of a crack is found with a dye or a low angle light and drilled, which is the step that stops it from running further during the repair.
- Tapered scarf back to sound laminate
- Material is removed on a long taper rather than a square cut, so the new layup has a wide bonding area instead of a butt joint.
- Layup in a planned schedule
- Mat, roving and where needed biaxial fabric go in as planned layers, each rolled to drive out air, rather than a single thick application.
- Backing support for through punctures
- Any hole gets structural support behind it before front side layup begins. Filling a hole from the front alone leaves a plug, not a repair.
- Fairing, priming and finish work
- Glazing putty and urethane surfacer are blocked flat, then the area is gelcoated or refinished depending on what the surrounding surface is.
- Load path correction on a repeat crackwhere applicable
- Where a crack has returned before, the bracket, fastener or opening corner responsible is addressed as part of the job.
How the work runs
Find the real ends of the crack
30 to 60 minutes
Cracks run further than they show. A dye penetrant or a light held nearly flat against the surface reveals the true tip. That point gets marked, because everything from here forward is measured out from it rather than from where the paint is open.
Stop drill and open the damage
1 to 3 hours
A small hole drilled at each crack tip removes the stress concentration that keeps the fracture moving. Then the damaged laminate is ground open along its full length so the true extent of the break is visible rather than assumed, and the owner gets photographs of what came out before anything goes back in.
Cut the scarf
1 to 5 hours
The opening is tapered outward at a shallow angle so the repair has a broad bonding surface. A short crack in a thick molded cap routinely produces a ground area several times the length of the crack itself, and that surprises owners more than any other step here.
Lay up and cure
2 to 8 hours
Mat goes in first against the scarf for conformability, then roving or biaxial fabric for strength, catalyzed at a ratio set to the bay temperature that day. Each stage is rolled out and allowed to cure before the next, and the final layer sits slightly proud for fairing.
Fair and finish
3 to 12 hours
Glazing putty fills the weave, a long board blocks it straight, and urethane surfacer goes on before final sanding. Gelcoated caps get patch gelcoat and are cut back. Painted surfaces are sealed, based and cleared out to a natural break.
What this costs
$600 to $5,500
3 to 26 labor hours at $210 per hour, body and paint.
- Paint supplies at $55 per paint hour.
- Body supplies at $5 per body hour.
- Hazmat and disposal $45 flat when chemicals, refrigerant or LP is involved.
- Parts at $100 or less carry 100 percent markup. Parts over $100 carry 35 percent. Special order parts require a full non refundable deposit at order.
- Sales tax of 7.75 percent applies to parts and materials. Labor is not taxed.
- A 50 percent deposit is taken at authorization on any job over $2,000, with an additional 25 percent when parts arrive on any job over $10,000. Final balance is due at pickup.
- A single short crack in an accessible flat area with a local blend sits at the bottom of this range.
- A multi leg star through a molded cap with backing work and a front refinish sits at the top.
- Repairs that also need a bracket relocated or an opening corner radiused add hours beyond the laminate work itself.
How estimating is billed
- Written repair estimate: $150, credited in full against an authorized repair.
- In depth diagnostic, scan and programming: $285 per hour, one hour minimum, credited in full against an authorized repair.
- In shop pre purchase inspection: $400 to $1,200 depending on unit size and systems count.
- Insurance walk ins are accepted during posted hours. All inspection and estimating work is performed in shop at the Yorba Linda facility.
What you will notice first
- A white star with legs running out of a single impact point
- A crack that gets measurably longer between one trip and the next
- A hole with the edges pushed inward and fibers standing up around it
- Hairline cracks reappearing in the same spot within months of a previous repair
- A crack running out of the corner of a compartment door opening
- Daylight visible from inside a storage bay where there should be none
- A chip that has opened into a line since the last time you washed the unit
- A dull grey halo around a crack, which is water that has already wicked into the mat
How this fails, and what we do about it
| Failure mode | How we diagnose it | The fix |
|---|---|---|
| Star crack from a point impact | Legs radiate from one center. Tapping around the star shows the fracture extends past where the gelcoat is visibly open, usually by an inch or more on each leg. | Drill a stop hole at each leg tip, grind the whole star to a tapered scarf past every drilled hole, then rebuild in mat and roving before fairing and refinishing. |
| Through puncture with no rear access | A hole with inward deformed edges in a panel you cannot reach from behind, such as a molded cap section or a closed sidewall cavity. | Insert a backing plate through the hole, wire or bond it against the inside face, then lay up onto that backing from the front and fair the front surface flat. |
| Recurring stress crack | The same crack returns after a cosmetic repair, often in the same length and direction. That is a load path problem, not a surface problem, and grinding it again will produce the same result. | Rebuild the laminate with directional fabric across the crack line, then remove the source of the flex with a backing plate, a bracket relocation or a radiused opening corner. |
| Water wicked into a cracked laminate | A grey or darkened halo surrounds the crack and the mat feels damp when the gelcoat is opened. Moisture travels along glass fibers for surprising distances. | Grind out the wet mat entirely and let the area dry under heat before layup. Resin will not bond to damp glass and a repair laid over wet mat will blister. |
Why it happened
- Road debris at highway speed, which delivers a concentrated point load and starts a star fracture even when it leaves very little mark
- Low branches on canyon roads off Santa Margarita Parkway, which drag along a sidewall and catch a rail, a light or an awning arm
- Corner contact while backing in a storage lot, where the impact point is a bollard and the panel has no support behind it
- Stress concentration at an opening corner, since any square cut opening in a laminate wants to crack diagonally out of its corners unless it was radiused
- Accessory brackets fastened through skin with no backing plate, which flex the laminate a fraction of a millimeter on every road input until it fractures
- An earlier repair done in filler, which is stiffer than the panel around it and simply moves the crack to the edge of the patch
Parts and brands we work with
- Polyester and vinylester laminating resin with MEKP catalyst measured to shop temperature
- 1.5 ounce chopped strand mat and 18 ounce woven roving
- 1708 stitched biaxial fabric for repairs that need directional strength
- Tinted and clear patch gelcoat with surfacing wax additive
- Polyester glazing putty and two component urethane primer surfacer
- Aluminum and fiberglass backing plates for punctures with no rear access
What not to try yourself
- Running a bead of sealant along a crack to keep water out until you can get to it. Sealant contaminates the surface and every bit of it has to be ground away before resin will bond.
- Skipping the stop drill because the crack looks stable. A crack tip is a stress riser, and grinding around it without relieving it usually extends the fracture during the repair.
- Filling a hole with expanding foam and glassing over the top. Foam moves with temperature, and the patch above it will crack along its perimeter within a year.
- Laying up over damp mat to save a day of drying. Resin will not wet out wet glass, and the repair will blister at the first stretch of hot weather.
Which vehicles we do this on
Vehicles we perform Cracks and Holes on
Diesel PusherDiesel pusher repair means working on a rear engine coach built on a welded Freightliner XC or Spartan rail, with a full body painted fiberglass shell and large basement baysClass CClass C motorhome repair centers on the cabover bunk, the joint where the coach body meets the factory van cab, and the stick built or laminated house behind itTravel TrailerTravel trailer repair covers A frame tongue welds, the front cap that takes road debris, the roof front radius seam, sidewall delamination starting at a window corner, and equalizer and axle wearToy HaulerToy hauler fifth wheel repair concentrates on the ramp door hinge line at the rear wall, garage floor deflection between crossmembers, and sag in the frame cantilevered behind the axlesOff RoadOff road trailer repair covers the articulating coupler pin and bushings, trailing arm and suspension bracket welds, dust sealing at hatches, and body to frame mount fatigueFood TruckFood truck repair covers the step van body, the serving window aperture and its header, the roof hood curb, the coved floor under the cooking line and the generator compartmentOwners always flinch when they see how much bigger the ground area is than the crack. I tell them the crack is the part you can see and the fracture is the part you cannot, and then I hand them a light and let them hold it flat against the panel themselves. Once somebody sees three more inches of crack that were invisible from arm's length, nobody argues about the scarf. The other thing I say: if a crack has come back on you twice already, we are not fixing the crack this time, we are fixing whatever keeps bending that panel.
Appendix: questions and answers
- Can a crack in RV fiberglass just be filled and painted?
- No. Body filler has no tensile strength, so the broken laminate underneath keeps moving and prints the crack straight back through the finish, usually within one hot season. The fractured material has to be removed and replaced with glass and resin for the repair to carry load again.
- What is a stop drill and why does my repair need one?
- A small hole drilled precisely at the tip of a crack. A sharp crack tip concentrates stress and keeps the fracture running. A round hole spreads that stress out and halts it. It takes two minutes and it prevents the crack from extending while the surrounding area is being ground open.
- Why did my fiberglass crack come back in exactly the same place?
- Because it is a stress crack and the source of the flex was never removed. Something behind that panel is moving, usually a bracket without a backing plate or a square cut opening corner. Rebuilding the laminate is only half the job. The second half is stopping the panel from bending there.
- How do you repair a hole you cannot reach from behind?
- A backing plate is fed through the hole, then bonded or wired flat against the inside face to give the layup something to build on. Glass goes on from the front onto that backing. It is a standard marine method and it produces a repair that carries load, unlike filling the hole from the front alone.
- Is it safe to drive with a cracked fiberglass panel?
- Short trips are usually fine on a small crack in a non structural panel, but the crack will grow. Highway wind load and heat cycling both extend it. What genuinely should not wait is any crack that lets water into the laminate, because wet mat turns a surface repair into a much larger one.
- Will the repaired area be visible when the work is finished?
- Not if the refinish is carried to a natural break. A patch stopped at the edge of the repair is always findable in low sun. Taken out to a molding, a rail or a body line, the transition falls where your eye already expects a change and the repair reads as original panel.
Open a file on this repair
Tell us the vehicle, what happened and whether a claim is open. We will tell you what the scope looks like and what it takes to get you back on the road.
Or call (949) 799-3387