Auto Rust Repair: How To Repair a Rust Hole

Auto Rust Repair – In part 1, we are going to learn how to cut out a rust hole.

This is part I of auto rust repair tutorial.  This lesson we are going to talk about cutting out the rusted damaged area and welding in a new piece of metal.

Determine Extent of Rust

The first thing you want to do is determine, where the rust is located and the extent of the rust. Rust is really not that hard to find. Obviously, if there is a hole, that is easy to find, but a lot of time the rust does not eat all of the way through the metal you may be able to repair the rust without having to cut out a section of the panel and adding a new piece to the panel.

Where Does Rust Come From?

Rust starts forming on the metal underneath the paint or from the backside. For different reasons, it could be due to salt on the roads that cause rust, it could be mud getting caught behind this area and not being cleaned, which results in the moisture causing it to rust, it could have had a repair in this area before and didn’t have the proper corrosion protection applied to the metal.  But for whatever reason, the rust starts forming on the metal. At this point you can’t see it, but as it starts spreading and growing it starts pushing the paint out and will bubbling the paint outward.

The First Indication Of Rust

When you see bubbled paint, this is the first indication there may be rust underneath it. This is the time you want take action and repair the rusted area.  At this stage you may not have to cut the rusted area out and replace it with a patch panel repair panel.

Determining The Extent of Rust

To determine how bad the rust is, use a screw driver or scratch awl to push on the bubbled area.  This will flake some of the rust out, but if does not push through, you may able to clean that area up, grind to bare metal, and apply corrosion protection.  The the part can be refinished, which will protect the panel from rusting again.

A Rust Hole

If the screw driver or scratch awl does push through or if it is too extensive to repair, it is going to require cutting out the rusted surface and replace area with new metal.

Before Cutting

Before you start cutting determine how big of an area needs to be removed.  Just because you have a quarter size hole does not mean that the rust is just in that area. Chances are it has spread behind the panel more than that.  So you want to grind the rust area to the metal and make sure the outside rust is removed.  Now you should be able to determine how thick the metal is around the edges.  You want to make your patch big enough to where the new patch is going to be welded to good metal on the panel.  Most of the time you are going to have to extend out where the rust was present to three or four inches past the area to assure  you are going to be cutting and welding to good metal.

Marking The Cut Line

Once you have determined where to cut, the easiest way I have found to mark the cut line is to use masking tape.  It is really not that necessary to spend a lot of time measuring to make perfect measured mark lines, as the piece cut out is what will be use as a template to make the patch repair.  I lay out the masking tape around the area to be cut out and use the masking tape edge make the cut.  Many time you will be by an edge flange where the metal wraps around the panel.  There will be several spot welds on the inside of the flange, which will need to be drilled out.

Making The Cut

Once the tape is  laid out use a cut off saw to make the cut along the tape edge.  Care must be taken not to cut into any inner panels, as you do not want to cut into inner panels.  You may have to carefully cut the outside panel taking care not to cut all the way through other components of the car.

Following the tape line, make the cut all the way around the rusted area and drill out the spot welds if there are any on the flange area.  Try to remove the rusted area with a little damage to it as possible.  The piece need to be removed if one piece if possible so it can be used as a template when making the new patch panel.  When the entire edge is rusted, the panel can’t really use the entire piece. In this case, use masking tape to lay out the shape of the panel.

Check Metal For Thickness

Make sure that your edges are good metal that you will be welding to.  Now you are ready to start fabricating your new panel or preparing a pre-shaped repair panel that can be purchased.  Pre-shaped repair panels make the job much easier, but with a few basic tools, you can fabricate some of the panels yourself, if they are not too complex or have multiple body lines.