How to Repair a Hole in the Floor of a Car

by Jesse James Dean
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In some states a vehicle will not pass inspection if it has a hole in the floor, and having this repaired by your local auto mechanic can cost you hundreds of dollars. So whether you are restoring an old hot rod or trying to get another year of service out of an old car, fixing the hole in the floorboard can be done yourself. This will save you a great deal of money and give you the confidence and knowledge to move onto more challenging holes in your vehicle.

Step 1

Remove all fire hazards. Because you will be working with tools such as a grinder and welder, it's very important to remove any carpet and upholstery. You will also want to cover anything flammable with a fireproof blanket.

Step 2

Cut out the rust. To repair this hole correctly, you must first cut away any rusted or thin metal surrounding the hole so that you have a good surface to weld a patch. Using a grinder with a cutting wheel, cut away the rust or thin metal in as uniform a shape as possible so your patch looks professional. Then use your grinder to remove any paint 2 inches around from the edge of the cut. This will leave a clean, weldable surface.

Step 3

Make the patch. Measure the patch area with a tape measure or ruler, then mark out an equivalent-gauge piece of sheet metal, adding 1 inch to all sides so you have something to weld to.

Step 4

Tack weld the patch in place. Hold the patch in place with one hand, and use your mig welder to tack weld all four corners of the patch on the outside of the vehicle. Repeat this process inside the vehicle. Now you may begin welding it 2 inches at a time. Alternate sides while welding to prevent the floor from warping. Weld both inside and out.

Step 5

Undercoat and paint. The outside of the patch will need more protection from the weather than the inside. Using a spray rubberized undercoating from your local hardware store will provide this protection. A spray primer from your local hardware store will do the job for the inside of the floor as well. When the painting and undercoating is done, you may re-install the carpet and upholstery.

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