Putty is a paste-like paint used to fill deep dents that cannot be filled by other types of undercoat or secondary coats. There are three types of commonly used fillers/putties:

Apply fillers/putties selectively, depending on the depth of the dent to be filled. Putty is normally applied thickly by a body filler scoop, or spatula, to fill the dent, then sanded smooth later.

A dual-component paint mainly consisting of an unsaturated polyester resin. It hardens when mixed with organic peroxides (hardener). This putty is used mainly to correct surface irregularities on the base metal during sheet metal repair. It is very flexible and can be applied in very thick coats up to around 30 mm (1.2 in). Metal putty is very porous and is difficult to sand.

A dual-component paint mainly consisting of an oil-modified unsaturated polyester resin. It hardens when mixed with organic peroxides (hardener). This putty is used mainly to correct pores and shallow dents remaining after application of metal putty. It has a very fine and flexible texture and primer-surfacer can be applied directly over it. It cannot be applied to in a thick coat approx. over 3 mm (0.12 in). This putty should not be applied directly over the bare metal due to low adhesion under those conditions.

This is a single-component putty mainly consisting of nitrocellulose and alkyd or acrylic resin. It is used mainly to fill shallow sanding scratches, pores, or dents remaining after the primer-surfacer application.

NOTE: Presently, there is a combination putty available which combine the best characteristics of several different putty types into one.

Thickness Limitation of Putty:
There are limitations to the application thickness, which vary by filler or putty type can be applied at once per putty type.