Two important rules should be observed when using abrasive paper:
1.) Always work with the grain.
2.) Avoid excessive pressure.
Circular or cross strokes during sandpapering break up the cell structure of the wood. The resultant marks are most difficult to remove - this particularly applies when stain is to be used afterwards as they provide harbours for applied stain or filler and spoil the general effect.
Excessive pressure during sanding does not allow the grit on the paper to fulfill its cutting purpose. Heat due to friction from the overloaded cutting surface causes the grit to break away from the paper and scratch the job.
Hold the sanding block at 45 degrees, with the long edge facing the direction of travel. This helps to prevent the edges of the sandpaper from catching on the wood and tearing.
Dry sanding - for raw surface preparation before finish is applied. General grades of paper to use : 80, 120, 180, 240, 320 grit open face. These would suit most timbers - start with the finest grade that is suited to the current surface. DON'T MISS A GRADE !
Wet Sandng - after finish applied and allowed to cure an intermediate or final step is to ensure the surface is flat by wet sanding. Wet sanding is not recommended if the finish is very thin as it is most important not to rub through the finish to the timber surface. If this occurs it may not be possible to disguise the rub through.
General grades of paper to use: 400, 800, 1200 grit wet & dry. Used wet with (typically) diluted red oil as a lubricant depending on the type of material being cut back, thinned wood oil is excellent as a lubricant for cutting back oiled surfaces, as it adds a coat of oil at the same time.
Steel Wool - Can be used both dry or with oil on raw or finished timber - useful for compound curves etc. Use a generous handful, not little pieces which are inclined to cut unevenly. Make sure all particles are removed from surface by blowing or wiping with a clean soft cloth or tack rag before proceeding to next step.
General grades to use are: 0, 00, 000 and 0000. 0 is fairly loosely equivalent to 180 grit paper, 000 to a very worn 360 grit. 000 and 0000 grade steel wool are referred to as french polishing grades.
N.B.- regardless of the abrasive, the finer the grade, the faster it cuts, as there are more cutting edges for a given area.
For using a scraper to clean up sanded surfaces, refer to the tool section.