Step 3 – Filling with Expanding Foam
If the primer coat that was first applied is dry, the hole can be filled with the expanding foam. This process might require cardboard supports to keep the liquid foam inside the hole to be filled. The foam should be applied so that it not only fills the hole but overfills it. The reason for overfilling the hole is because the excess foam will be cut away after it dries. This excess expanding foam is what allows shaping the surface that body filler will be applied to.