There are a large number of DIY tasks for which sandpaper is useful but to get the best performance from it, it is also necessary to know which sandpaper grit is required for each particular job. Knowing how to determine the grit of sandpaper by sight can make life much easier.
Depending on the brand of sandpaper you use, you may find that the manufacturer incorporates symbols, signs or lettering that confirms the grade just by looking at it. Similarly, if sandpaper is available on a roll, you may find that different sizes are used to differentiate the sandpaper grit grades. Working out the grade of sandpaper with this method is easier to do when you regularly use the same brand of sandpaper.
When you are using sandpaper of different grades that originate from the same manufacturer, you are likely to find that the color of the sandpaper differs according to the coarseness of it. Knowing what color relates to which grade of sandpaper will enable you to work out the grade that you have just by looking at it. The finest grades (ie highest grit) of sandpaper will often be a darker color and will gradually change to a lighter color as the coarseness increases (ie the grit decreases).
One of the best ways to determine what sandpaper grit you have by sight alone is to simply consider the size of the actual grit attached to the paper. The highest levels of coarseness will look bumpy and you will find it easier to see individual grains of grit. By contrast, the surface of fine sandpaper will look much more even and the grains of grit will be smaller.
Markings on Rear
No matter whether you are using small sheets of sandpaper or a section of a large roll, you will find that the reverse of the sheet usually outlines information in relation to the grade of the sandpaper. This will tend to be series of numbers that relate to the grade of the sandpaper.
The thickness of the backing paper will differ according to the size of the sandpaper grit due to the fact that they have different uses. It will be necessary for the backing of coarse sandpaper to be almost thick enough to be classed as card so that it can stand up to the heavy-duty work it is required for. The fine sandpaper that is used for lighter jobs can be constructed with a thinner backing as it will not be necessary to be so vigorous while using it.
A good way of determining the grade of sandpaper grit by sight is to make use of the light. By holding the surface of the sandpaper up to direct light, you will be able to see the glittering of the grit. The larger particles of coarse/low grit will glitter less or not at all when you move it, and over only a small amount of the surface at a time. Fine/high grit will produce a softer glittering light over a significant surface area.