All primer and filler coats must be thoroughly hard dry before any sanding and final preparation is carried out.
Final sanding before applying colour coats is generally carried out wet using the appropriate fine grades of WetorDry abrasive paper. Small areas can be sanded dry but a finer finish and extended abrasive life is achieved by wet sanding.
Preparation for solid colours can be with 500 grit or finer WetorDry papers, but metallics and basecoats will need final flatting with no coarser than 800 grit, preferably finer. The use of coarser grades of WetorDry will result in visible sand scratches which will show through the final finish, even if extra coats are applied.
Users of power tools, particularly D.A. sanders, can use 320 grit or finer for solid colours, but basecoat metallic finishes are best finished with finer grades of WetorDry paper.
Large areas or vehicles which do not need to be 100% perfect can be sanded with orbital or d/a sanders using dry abrasives, but the final finish is usually lower quality than if hand flatted
If the existing paint around door handles, wiper spindles etc. is in good condition and only needs to be sanded to `key’ the new paint, abrasive nylon pads, commonly 3 M’s Scotchbrite, are available in suitable grades from motor factors. As they are soft and flexible access to difficult corners is made much easier.
Final preparations and panel cleaning
Primered areas should be given a very light `guide coat’ to ensure the surface is fully flatted. This will highlight any dry spray, pinholes or unflatted primer as the surface is sanded.
Sand all panels using a flat sanding block with plenty of clean water. Take care not to leave gouges with the edge of the block, or by applying to much pressure while sanding. Light, even strokes are all that is needed for efficient sanding, avoiding circular motions which tend to show through the final coats. All areas that are to have paint applied must be sanded until the surface is matt when dried, otherwise paint adhesion will be poor. Particular attention should be given to panel edges and areas where trims or mouldings could not be removed, especially awkward places such as around door handles or wiper spindles.
As each panel is sanded wash the residue away before it dries, as some paints and primers can leave a slurry that sets almost as hard as the original material. Rinse and then dry all the repaired panels with absorbent cloth. Do not leave water to dry naturally on the panels, as this may cause problems with lime or contaminants in the water affecting the finish at a later stage.