How to Fill Trim Holes

Other than an oxyacetylene torch, a DA grinder, and some rags, here’s what you’ll need for lead work: a cartridge respirator, paddle lube, aluminum body tape, scissors, a pencil, an acid brush, a wooden paddle, a countersink, tinning compound, and lead solder sticks.

Cutting loose the body side mouldings from our 1970 Dart left a row of mounting holes along the delicate character line. Plastic filler would require dimpling the holes to gain a modest chance of it properly adhering and would necessitate slopping it along the full length of the body and blocking in a new line. With lead, the surface thickness of the repair is negligible, preserving the original line. Prep for solder by sanding to bare metal around the hole.

Next, use the countersinking bit to clean the inner edge and provide a larger, tapered surface area for the lead plug to bite

Now the hole is ready for tinning flux. While some brands come as a premixed paste, we used Dutch Boy Acro-Tin, which is the dry-powder type. Forget the instructions on the can--just stir up your own paste with tap water. Mix to a heavy consistency about as thick as valve lapping compound. Make only enough for the job at hand.

Using the acid brush, paint the edges of the hole and a half-inch area around it with the tinning slurry.

Using a small torch tip (Victor No. 000 used here), play the flame evenly around the tinning paste until the solder in it melts to the repair area. A low, even flame is all it takes; hold back the tip a couple of inches to control the heat. Remember, we’re not welding here. The tinning compound will turn bright as the area is tinned, telling you when it’s done.

While the tinning film is still warm, wipe it with a damp cotton rag to clean off the flux and debris at the surface. One thorough wipe works best.

With the area tinned, the body solder has something to stick to. Play the flame over the repair area and the lead stick, and drop enough solder to fill the hole, placing it just above the hole. The trick is to dab and rotate the lead stick as its tip begins to melt.

This is about the right size for the lump of lead deposited adjacent to the hole. The lead can be heated and moved anywhere on the tinned area. We positioned it above the hole so that it can be dropped like a curtain over the repair.

Spread the heated lead with the wooden paddle. In keeping with our low-buck approach, our paddle was harvested from a broom handle and sanded to shape. To prevent the lead from sticking to the paddle and smearing, the paddle must be lubed by playing some heat on the business end of the paddle (don’t burn it) and sliding it over the lube. Once coated, warm the lubed area and wipe off any excess with a dry rag. To move the lead, again play a low heat in the area of the repair, and when it just starts to yield (check by jabbing with the paddle), spread the solder into position.

Work the lead until it smoothly covers the repair area. Controlling the heat with the torch position is key, although it’s not too tricky after some practice. Overheat the lead and it’ll drop out; try and work it when it’s too cold and it’ll get too grainy as you spread it. Finally, don’t blast the paddle directly with the flame--it’s wood, you know.

While finishing large areas generally calls for the lead file, the DA sander alone will get the job done handily for a simple hole repair. The lead should be feathered into the surrounding sheetmetal rather than ground down to a button. We used a 40-grit sanding disk with the DA locked off to the grind setting to quickly feather the repair and then reset to orbital mode for the final blend.

The almost invisible finished metal repair is blended smoothly into the surrounding sheetmetal and, unlike plastic, won’t drop out or put a crowned area over the repair. The entire leading process can be completed in about two minutes or about the time it takes for a hot mix of plastic to cure. Finish with metal prep/conditioner to clean and primer up.

The last thing we want to see on the backside of holes such as these, which are visible from inside the trunk, is the rough side of the repair. Sure, the inside can be ground and finished to impress the local alignment man, but crawling under the wheelwell to wield a sander is undeserved penance

The trick is to back up the repair with aluminum body tape, which actually forms a mold at the back of the hole. The problem is that the adhesive will flame up and the residue will foul the repair. The ruse? Cut a button of tape slightly larger than the hole and stick it shiny side up to the center of a piece of backing tape.

Mark the center of the tape button so that it can be lined up with the center of the hole.

Tape won’t stick to an oily, wet, or dirty surface, so clean the backing area thoroughly. Finish by centering the tape button over the hole and pressing the backing tape firmly to the surface.

No, it’s not the latest image from the Mars Pathfinder but rather the factory-painted undercoating on the inside of our Dart’s trunk. With the backing tape removed, the inside of our repair is perfectly formed to the inner surface. Notice that the heat of the leading process was so low that even the asphalt undercoat immediately surrounding the hole was left unscathed. Try that with your MIG or brass rod.