Abrasive Selection for Sanding and Working Down

The sanding operation generally requires using a sequence of abrasive grit sizes, coarse (16-40 grit), intermediate (50-80 grit), and fine (100 grit upwards). Whichever sequence of abrasives is used will be largely dictated by the condition of the floor. Care should be taken by the contractor to ensure that initially the finest possible abrasive is used which is still effective enough to successfully prepare the floor.
Coarse grit sizes will level the floor and remove old seal and imperfections. This is an aggressive process which will leave scratches in the floor. The intermediate and fine grades of abrasives serve to remove these marks.
Whatever grit size of abrasive is used for the initial sanding, don't omit more than one grit size for the following sandings. Failure to do so will leave scratches in the timber which are too large to be removed by fine abrasives, resulting in a more textured surface. This will impair the performance of any applied sealant or lacquer.
After sanding with each abrasive size, remember to remove any residue from the abrasives, along with sanding dust, by vacuuming.
Incidentally, the type of abrasive used can also impact on the effectiveness of the sanding operation. Zirconium abrasives are extremely hardwearing which can be useful when using coarser grit sizes. Slightly softer abrasive material, such as silicon carbide and aluminium oxide, can offer advantageswith finer grit sizes as they are less likely to put harsh scratches in the timber. But it may be wasteful to use the slightly more costly zirconium abrasives on a floor where contaminants, such as wax or previous lacquer treatments, will rapidly clog and reduce their cutting ability.
Fine sanding should be finished with either 100 or 120 grit abrasives, but to limit any grain raising that occurs with water based finishes then 120 grit should be used. If the timber is to be stained or oiled, finishing with 100 grit is advisable to maximise penetration of the product.
If the floor is finished with coarser abrasives the surface texture of the timber will be increased. This will impact aesthetically but will also result in a reduction of surface build from any sealant, reducing wear resistance.
In the case of an oil treatment, the increased texture will trap dirt and grit making the floor more difficult to maintain.