The surfaces of the pieces of wood we have worked with need refinement at some stage. Cut surfaces are usually sanded a little at the end of each sawing process. Sanding is also a way of checking your workpiece. After you have finished your workpiece and before painting it, sanding all its surface is often required.
There are many different types of sanding material, mainly emery, flint, glass or carborundum gains attached to a paper or textile backing surface. The lifetime of the sandpaper depends on how hard the grains are. This is usually indicated by colours: yellow is the softest, followed by greyish yellow, brown, and red carborondum sandpaper is the hardest. The size of the grains determines what they can be used for, indicated by a numbering between P27-P2500 printed on the back of the sandpaper. The smaller the number, the coarser, and the bigger the number, the finer the sandpaper is. For the workpieces described here, sandpapers between P40 and P280 should be used. You can read about grains sizes in more detail in the chapter about sharpening tools.
Coarser sandpaper of the size 40 is used for removing substantial amounts. In order to avoid that larger than average grains leave marks on the surface sanded, I always rub the sandpaper on a clean concrete surface before starting work.
It depends on the quality of the surface how fine sandpaper should first be used. Do not start sanding a smooth surface with coarse sandpaper: that way you’d only make it uglier. In general, however, we should start with coarser sandpaper and proceed to finer ones. When using coarse sandpaper, press it less strongly at the edges of the strip or the plywood to avoid the rippling of wood fibres the way I described in the chapter on the use of rasps. Sanding should be performed first across the grain and then in the direction of the grain; it should always be finished in the direction of the grain. Surface defects, indentations and scratches are easier to detect by wash light: if possible this is how you should check the surfaces.
(Workpiece lit by wash light)
Always use a sanding block for sanding. You can buy or make one or, if necessary, use sandpaper by attaching it to a piece of wood. Sanding should always be done in a horizontal position, with even and long movements. Leave the edges to the end and sand them with careful, longitudinal movements. You can make various sanding profiles, too, to be used in hard to access places. I have sandpaper glued on a big nail and on round pieces of wood.
(Sanding blocks of various profiles)
If you want a very fine surface after sanding, you can wipe the workpiece with a wet sponge. Some of the fibres soak up water, become chaotic after drying but after sanding once again the surface becomes smoother.
Smaller damage can be removed by sanding, to be performed by supporting the sandpaper with your index finger only.
(Sanding with the support of your index finger)
Joining defects, too, can be improved by sanding. Apply some glue to the imperfect joints where the two joined pieces stand apart, wait a while and sand the surface with used sandpaper, by short movements. The sanding dust gets stuck in the joint and fills up the surface. After drying, carefully repeat the sanding.
(Joining defect with glue)
(The joining defect after sanding)
Your sandpaper will last longer if you blow the dust stuck into it or remove it using a brush.
Sandpaper wears off faster at the edges. After a part of it has worn off, fix the paper on the sanding block a little further on and keep repeating this until all its surface has worn off.
If you want to purchase an electric sanding machine, I recommend buying the simplest vibrating sander. It is easier to sand small horizontal surfaces with this than with an orbital sander. Always comply with the safety instructions of the machine.