Abrasive materials

What wall materials are used most often?

The most common are sandpaper, canvases, fiber, poem, pastes and flour. Painters and varnishers often use sandpaper. Abrasive cloth is relatively expensive and therefore painters use it less frequently. Abrasive fiber is used for rough grinding with rotary and angle grinders. As abrasive grain for sandpaper, for cloths and fibers, silicon carbide is mostly used with a hardness 9,8 on the Mohs scale or electrocorundum with hardness 9,5. Abrasive papers are produced and used, depending on the type of binder, as dry and wet sanding papers. For many sanding jobs, e.g. treatment of aluminum and zinc surfaces, as well as for matting old coatings, the use of a sanding fleece has been adopted. The abrasive grain of silicon carbide or aluminum oxide is in this case bonded with a plastic fleece.
Abrasive pastes are only used for finishing polishing. Pumice flour is used for sanding varnish, so today its significance is also minor.

Suppose, that the sandpaper has the symbol P on the back 120.
Please explain this marking
Symbol P 120 is the size of the abrasive grain. This is the number of meshes per square inch, through which the abrasive grain has been screened during production. The letter P stands for, that it is a standardized abrasive, in which the proportion of smaller grain was limited.

What grit of abrasive in the varnishing of metal surfaces is suitable for:
a) rough rust removal and leveling of weld surfaces?
b) removing coatings?
c) sanding layers of polyester putty?
d) grinding fillers?
e) matting of undamaged old paint coatings? The grit selection of the abrasive depends on this, whether grinding is done manually or mechanically and on the type of grinder.

The following overview may be helpful: