Dent Removal and Repair, in detail

Three constructions give three completely different dents. An aluminium skinned trailer or older coach is thin sheet fastened over vertical studs with adhesive between them: an impact between studs leaves a shallow oval bruise, and an impact on a stud leaves a crease with the stud line visible straight down the middle. A laminated fiberglass sidewall is skin, adhesive, foam or Azdel, then interior panel, so an impact crushes the core and the surface dent is the smallest part of the damage while the bond around it has usually let go. A steel cab door or truck fender dents like a car, which is to say it can be pulled and worked back.

Reading which one you have takes a light held at a low angle and a hand on the inside where that is possible. Crushed core gives a dent that feels slightly soft at its centre and often shows a faint ring where the skin separated. A simple aluminium bruise stays crisp and springs a little when pressed. Getting that wrong is how a dent repair turns into a delamination job two months later, so a suspect panel gets tapped, sounded and photographed before anybody quotes it.

Paintless dent repair works by moving metal from behind with precise leverage while the paint stretches along with it. Three conditions have to hold: the panel is metal with enough ductility, the paint is flexible and undamaged, and a tool can physically reach the back of the dent. A car body satisfies all three routinely. An RV sidewall satisfies almost none of them.

Access behind a laminated wall does not exist, because the wall is glued to a core and finished on the inside. Gelcoat and thick coach paint crack rather than stretch. Studs, wiring, plumbing runs and cabinet backs occupy the space a tool would need. Paintless repair has a genuine place on the steel parts of a rig, a cab door, a hood, a fender, a van side panel, and there it is the cheap correct answer while the paint is intact. Anybody offering it on a fiberglass motorhome sidewall is describing something else.

Where a panel can be reached from inside, the repair gets dramatically better and cheaper. On a Sprinter or cargo van that means pulling a wall liner, shelving or a headliner. On a box truck it can mean removing an interior liner panel. On a coach it can mean emptying and removing the back of a cabinet, lifting a bunk, or taking off an interior wall panel screwed under trim. The work to gain access is real hours, and it competes directly against the cost of working blind from the outside.

Access decides technique. From behind, a dent can be pushed with a dolly and levelled with very little filler. From the front only, the options are glue pulls, drilling and pulling, or filling, and each of those is either slower or leaves more material sitting on the panel. We quote both routes on anything marginal, with the honest note that taking a cabinet apart to avoid filler is often the better long term answer on a coach you intend to keep.

Steel gets pulled from the front by two established methods. Glue pull repair bonds a plastic tab to the panel with hot melt adhesive and pulls with a bridge or a slide hammer, lifting a dent without breaking the paint film or exposing bare steel. Stud welding tacks a pin to bare metal, pulls it, and grinds the pin off, which means paint has to come off first and the area needs primer afterwards. Glue pulling is first choice where paint is intact and staying. Stud welding is the answer where the panel is being refinished regardless.

Heat is where cheap work goes wrong. Steel can be shrunk with controlled heat by somebody who knows how far to take it. Aluminium mostly cannot: heat it enough to move and you anneal it, and a soft patch in a large flat panel oil cans in the sun for the rest of the vehicle's life. On aluminium the pull is mechanical, slow and incremental, and where metal has stretched past recovery the correct answer is replacing that skin section rather than continuing to work it.

• Glue pull tabs and a bridge where the paint is intact and staying
• Stud welding only where the panel is being refinished anyway
• Controlled heat shrinking on steel, never as a substitute for pulling
• Aluminium pulled mechanically and replaced where it has stretched past recovery

Filler is a levelling material with a working depth, and pretending otherwise is the most common cheat in the trade. Used thin over a properly pulled panel, polyester filler is entirely correct and lasts as long as the vehicle does. Used to bury a dent nobody pulled, it shrinks as it finishes curing, cracks over a flexing panel, and prints a shadow revealing the exact shape of the original damage in raking light inside a year or two.

Our rule is that shape gets made right mechanically first and filler only closes what is left. On a coach panel that also means respecting the substrate: filler over a crushed laminate core has nothing solid underneath it, and filler over an unsealed repair on aluminium in coastal air traps moisture against bare metal. A thick repair low on the sidewall of a trailer that lives near the water is where corrosion starts, with a smooth surface painted over the top of it.

Some dents are best left. A shallow bruise low on a slide box, behind a wheel, on a compartment door facing away from the patio side, or anywhere the repair means cutting into a sound painted panel to gain access. If the panel is sealed, the paint is intact and the dent is not visible from a normal standing position, the repair costs real money and buys very little. Nothing here is priced below $500, and a small dent can easily justify more than that once refinish and blend are added to it.

Two harder cases turn up on older coaches. On a body wearing a full painted graphic scheme, repairing a dent in the middle of the scheme means reproducing the scheme across the repair area, and the honest quote is often several times what an owner expected for a dent. On a coach heading toward a full repaint in the next year or two, the sensible plan is to leave cosmetic dents, fix anything that leaks, and address the rest together when the body is stripped. We will tell you when that is the case.

A dent in a steel cab door with intact paint, lifted with glue tabs, is a short job at the bottom of the band. What moves it up, in order: refinish area, since a dent in the middle of a large flat panel needs the whole panel plus a blend either side. Access, because interior disassembly is hours of work before any repair starts. Substrate, because a crushed laminate becomes a bond repair rather than a dent repair. And scheme, because a graphic crossing the damage has to be reproduced.

Supplements on dent work almost always come from substrate. A panel that looked like a simple bruise turns out to have a separated bond behind it, discovered when the panel is sounded or when the interior comes off. Photographs go to the carrier the same day rather than at the end of the job, because a supplement raised early costs days and a supplement raised late costs weeks.