Go over the damaged area with a brush to remove the rust powder from the remaining metal. Treat the damaged area with a rust inhibitor. If the reverse side of the damaged area is accessible, treat it as well.
Before applying putty, you need to close the hole. This can be done with zinc mesh, aluminum tape or polyurethane foam.
Zinc mesh is the best material for sealing large v holes. Cut a piece to the right size, then place it in the hole so the edges are on top of the surrounding body metal. The mesh can be secured in place with a few wads of putty around the perimeter.
Aluminum tape can be used for small or very narrow openings. Unwind a piece of the desired size from the skein and glue over the hole, putting the second piece covering the first if the width is not enough. Press the edges of the tape with the handle of a screwdriver so that it fits well on the metal base.
It is good to use polyurethane tape for holes located in places of the body with a complex configuration. The procedure for preparing the foam is as follows: mix equal amounts of liquid from the individual cans included in the kit in one vessel. Wait until the mass begins to thicken and pour it over the hole, placing a piece of cardboard. As the polyurethane begins to expand, it will protrude from any uncovered holes. After it has completely hardened, cut off the excess with a hacksaw blade.
ATTENTION: In case of large damage to the body, it is necessary to carry out a major overhaul, in which the damaged parts of the body are replaced.