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Trunk Floor Restore

The “ins and outs” of sheetmetal repair for a rusty trunk floor

Story Jim Black / Images Jim Mott - December 27, 2012 10:00 AM

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For Your Information:

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1 Here’s the trunk floor of our ’69 Charger. Surface rust is evident, but just how bad is it?

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2 Equipped from the factory with a vinyl top that trapped moisture, rust and perforations at the sail panel and lower window channel resulted, letting in rain and moisture.

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3 The body is placed on a rotisserie and the bottom media blasted. This is the quickest method to strip away paint and rust in hard-to-reach areas.

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4 We left the body on the rotisserie for better access to both sides of the trunk floor. The media blaster wasted no time prepping that portion of the trunk floor that obviously would need repair. Even a “light-dusting” of media blew holes through the trunk floor.

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5 After careful inspection we decided to save most of the trunk floor instead of doing a complete replacement. We marked out the area to be replaced using yellow tape, paying particular attention to locate the cut lines, so that the welds will be hidden from underneath by the floor bracing.

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6 We drilled out the spot welds that fell within our marked-out area, and using a cut-off saw, carefully cut out and removed the damaged floor section.

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7 Next, from the bottom side we filled and then ground all the spot weld locations in the cross brace previously drilled out. We’ll be spot welding in our new piece from the top side instead.

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8 We clamped the new two-piece floor section together and set it up on a rack for better accessibility. Then we carefully placed the cut-out section over our new panel, using it as a pattern. Using yellow tape, we went around the outer edges for our cut line and marked any missing plug holes or stampings not found in the new panel.

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9 Here’s a better view of the new two-piece floor panel from Classic Industries. After scribing the cut line, we removed the tape. Some adjustment to the rectangular gas tank filler hole and a missing hole-plug was noted and corrected.

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10 We carefully cut out the trunk repair section, fitted it in the car and trimmed as necessary. We traced out and drilled the spot weld plug holes from the braces and then welded the two floor halves together and ground down the seam, as shown.

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11 We carefully installed our replacement floor section from the top side, spot welding it through the plug holes. At the bottom, we began the time-consuming job of butt welding the edges. TIG welding provides the best heat control, but most hobbyists use a wire feed welder as shown here.

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12 We don’t run a continuous bead as this can heat up and warp adjacent panels. Instead, we space out the welds and fill them in later to avoid damage. Patience is the way to go.

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13 We applied filler to the welds after grinding and sanding smooth. If the weld heat is controlled, not much filler is required.

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14 Next, we moved to the spray booth, prepped the bottom of the car, and applied an epoxy primer coat over our repaired floor panel and bottom.

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15 Then we applied PPQ K-38 primer over all the seams and bottom in preparation for wet sanding. Note that we taped over any numerical sheetmetal stampings so they were not filled by primer.

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16 We sanded the trunk bottom with a D/A, and 320 grit discs.

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17 We continued to sand the entire car bottom, prepping it for final painting.

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18 We painted the bottom side with a factory gray epoxy, an in-house mix to match the original color.

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19 We sprayed on a coat of factory DY2 yellow (original color of car) instead of the gray epoxy used on the bottom. Any evidence of the repair is not visible from either side, and the factory seam sealer is still in place. We duplicated the factory overspray around the perimeter of the bottom using the DY2 code yellow.

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When it comes time to restore that classic muscle car, some sheetmetal repair is probably going to be required.

Most restorers can agree that the majority of repairs will almost always include the trunk floor, unless your car resided in a very dry climate like that found in the Southwest.

The recent restoration of a 1969 Dodge Charger by Jim Mott Restorations, of Kimberly, Idaho, included some major sheetmetal repair to the trunk floor. With Jim’s help, we decided to give readers a better understanding of how a trunk floor repair is accomplished and to provide some guidance to those “do-it-yourselfers” who might tackle a repair like this on their own.

Granted, not many garage enthusiasts have the equipment and know-how for this type of work, but with shop rates soaring, more and more enthusiasts are expanding out of their comfort zones, taking on tasks previously left to the professionals.

The big question for the restorer is how much sheetmetal should be removed? Our ’69 Charger had a vinyl top, which typically trapped moisture, causing rust and perforations around the front and rear windows. Most cars of the period clad in vinyl had serious issues with rust in the roof. Our ’69 Charger has some major perforations adjacent to the sail panels and along the bottom window channel, which naturally allowed water to enter the trunk, causing rust.

After having the car media blasted locally, Jim accessed the amount of sheetmetal work required for the restoration. “The only major repair would include the trunk floor,” he said. “Just a few spot repairs elsewhere.” We ordered a new two-piece trunk floor from Classic Industries.

Instead of replacing the entire floor with the new panel, Jim chose to remove and replace just that portion of the trunk floor that had damage. “I believe it’s best if we leave most of the original seams and spot welds intact whenever possible. That goes for the seam sealer as well. The cars just look more original.” Jim said a common mistake made by first time restorers is to cut out more original metal than necessary and then the repair becomes obvious.

We’ll carefully mark out the section of floor to be removed, drill out any spot welds in that section, and cut away the damaged portion. The cut-out section will be used as a pattern over the new replacement floor panel. A new piece will be cut out and welded in, seams ground smooth, filled, primed and painted.

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