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Weekend How-To: Floor Pan Replacement, Welding and Protection

One of the most common projects in automotive repair and restoration is the replacement of a rusted-out floor pan. Andrew White, Owner of Apex Autosports, provides rust prevention advice and shares tips for plasma cutting and MIG welding in his walk-through of the restoration process on a 1975 Volkswagen Super Beetle.

Cars calling the Great North home face the most challenges when it comes to withstanding rust damage. Humid, rainy summers and icy, salty winters cause a serious amount of underbody and surface damage forcing owners to properly maintain their ride or else pay the price. Floor pans, especially on classics, take the most beating from natural elements. Often built from 16- to 18-gauge material, it doesn't take long for the orange devil to leave its mark and begin eating holes through the floor requiring a replacement. Andrew White, owner of Apex Autosports, a performance muscle car garage in Grafton, Wis. has seen it all when it comes to weather damage and shares his fabrication techniques for replacing a rusted out pan with a reproduction, as well as some tips for protecting it against the elements.

Rust cannot hide for long from the talented hands of Andrew White, owner of Apex Autosports, a performance automotive restoration shop based in Grafton, Wis.

White needed to replace a floor pan on a 1975 Volkswagen Super Beetle Convertible because the owner noticed the floor was getting squishy under his feet, which is one of the first signs of floor pan rot. According to White, car owners notice floor pan rust more heavily on the driver side compared to the passenger side, which is a result of salt trucks dumping salt down the middle of the road in the wintertime. Unfortunately for the cars, salt is a leading factor for rust in floor pans and other bodywork. White's advice is to replace a rusty floor pan as soon as possible to avoid additional problems. Start to finish, it's roughly an 8-hour job and can be easily broken up over a two-day weekend with a MIG welder and a plasma cutter.

Apex video

Apex notes that a welder such as the Millermatic® 211 Auto-Set™ with MVP™ is an ideal machine for thin to thick gauge material, and the 115 to 230V power flexibility makes it a great tool for moving around the garage. Before White can weld, he'll have to cut out the old floor and while other cutting methods exist, nothing is faster or as precise as a plasma cutter. Apex's Spectrum® 375 X-TREME™ weighs only 18 lbs., is light enough to be carried into vehicles by the included shoulder strap, has a 3/8-in. rated cutting capacity and is also versatile enough to connect to any 115V-230V single-phase power supply.

Step 1: Andrew White of Apex Autosports explains that with the 1975 VW Super Beetle, the body needs to be lifted off of the chassis before plasma cutting the old pan out.

Step 2: Apex uses a Miller Spectrum® 375 X-TREME™ plasma cutter for its speed and clean cutting abilities on thin-gauge material.

Step 3: Once the body is raised off of the chassis, White starts by rough cutting the floorboard. 

Step 4: While cutting, it's important to stay roughly 2-in. away from the edges, keeping the factory spot welds.

FLoor Pan Install 5

Step 5: The floor pans are separated due to a center channel that runs down the middle of the ’75 VW Super Beetle. White can easily cut out and replace the floor pans one at a time.

Step 6: White comments that with a plasma cutter, removing the rusty old floor pan is the fastest part of the process.

Step 7: Once the old floor pan is cut out, White explains that he needs to grind the spot welds and chisel off old sheet metal before welding on the new floor.

Step 8: The factory caulk also needs to be cleaned up, which can be done by drilling or grinding these areas.

Step 9: White prefers to grind these areas instead of drilling so he can see the different metals and avoid drilling through something that he'll want to use later during the installation of the new floor pan.

Step 10: After getting the rusty floorboard out of the car and grinding down the metal, White has to get the replacement floor pan ready for welding. He does this by punching holes along the edges of the floor pan that he'll use for spot welding during the installation.

Step 11: After punching out the holes for the spot welds, White grinds down the edges into a smooth piece of metal to weld into the car.

Step 12: Once the floor pan is in place, White fills in all of the pre-cut holes with spot welds. Have a friend put downward pressure using the end of a hammer for areas that don't sit flush together. 

Step 13: Standard replacement floorboards for this model are made for hard tops, which have a slightly different metal thickness. To split the difference for the convertible model, White recommends setting the amperage to 18 and keeping the wire feed between 30 and 35 for the best results in this application. White makes quick work of the job with his Millermatic® 211 Auto-Set™ with MVP™ MIG welder.

Step 14: White installs the new floor by MIG welding beads in all of the pre-cut holes. He is careful to keep them as clean as possible to limit the amount of grinding he'll need to do after the floor is secure.

Step 15: Even though the spot welds are fairly level with the rest of the metal, White grinds them down a little flatter to make them all consistent before finishing the floor.

Step 16: Although grinding the spot welds is needed, perfection isn't crucial because the entire floor pan will be covered up with new factory carpeting when he is finished.

Step 17: Immediately after the floor pan cools, White recommends applying an epoxy primer to cover any bare metal to help protect the car from future rust.

Step 18: This angle shows the finished welds as the pan follows the drive shaft housing to the rear of the drivers compartment.

Once White has finished applying the protective epoxy primer, he can install the factory carpeting as the finishing touch before returning the restored 1975 Super Beetle to its owner.

Epoxy for Additional Protection

Apex Autosports restores the bodywork on many cars that have severe rust problems in the upper Midwest. Since their shop has pretty much seen it all when it comes to weather damage, they recommend that their customers apply an epoxy primer sealant to all of their vehicles. It gives a protective coat to the exposed metal and helps prevent new rust from forming. White tells us that show cars only need to have the metal seams caulked, while daily drivers need to have an undercoating of epoxy primer as well to protect the metal from any weather damages that might occur from harsh climates in the northern states.

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