There are many types of body fillers, but the best one works best with a hardener. In this case, you just need to strictly follow the manufacturer's recommendations. The filler is applied with a flexible rubber or plastic applicator. Mix a small amount of filler on a clean wooden or cardboard surface, use the hardener sparingly.
The following procedure should be followed for applying putty. Prepare the metal surface as described above. Prepare the putty according to the manufacturer's instructions. Apply the putty to the damaged area of the body panel using an applicator (spatula). To achieve the desired surface contour and putty level, each stroke of the applicator should go through the entire repaired surface. As soon as the contour of the putty surface approaches the original, stop applying the putty immediately, because when it hardens, it will begin to stick to the applicator, forming lumps and leaving burrs on the treated surface.
Apply layers of paste at intervals of about 20 minutes until the level of the putty surface becomes slightly convex above the surrounding metal panel. Allow the treated surface to dry completely and harden.
Remove excess putty layer using waterproof sandpaper. Start with coarse-grained paper type "N-180" and, gradually decreasing the graininess, finish the treatment with type "N-600". It is recommended to use imported materials due to their higher quality of abrasive and lining.
To achieve an adequate flatness of the treated surface, the paper should be pre-wrapped (or stick it on) around a wooden block (it is permissible to use rubber or foam).
During the processing, wet the paper with water regularly and generously. Continue the work until the surface being processed is absolutely smooth at the final stage.
At this stage, the treated surface should be a disk or oval of clean, shiny metal, ending in a gradually tapering edge of well-preserved paint.
Rinse the treated area with plenty of running water to remove even the smallest traces of abrasive formed during grinding.
Dry, degrease and dry the surface again with a hair dryer. Apply a thin layer of primer from an aerosol can, this will reveal all the defects made during sanding.
Eliminate any defects that are identified by applying a layer of fresh putty.
Repeat the sanding and grinding step. Repeat the filler, sanding and priming steps until you get a satisfactory result.
Finally, rinse the treated surface with running water and dry it. Now the surface is ready for painting.