Methods of Sanding Wooden Floors

The method for sanding a floor will be determined by the type of flooring present. Mosaic or herringbone floors should be sanded at 45° to avoid cuts going 90° across the grain. Floors comprised of strips or planks should be abraded at an angle of 7-15° to the grain for coarse grit sizes and parallel to the grain for fine sanding.
Where boards are cupped or height variation is present between adjacent pieces of timber, the floor should be sanded with coarse abrasives parallel to the boards in order to level the floor. Subsequent cuts should be made as with normal strip flooring with the final sanding running with the grain.
During sanding, each pass of the machine should consist of a forward and a backward sanding. This ensures that any standing timber fibres from the first sanding are cut back with the second. The following passes should overlap the previous one slightly to prevent missed areas. Sanding should continue with subsequent passes made so that the guide wheel of the machine (should it have one) runs on the newly sanded timber, allowing the machine to run as smoothly and level as possible.
To sand more effectively, the speed at which the machine moves across the floor should be varied. With coarse abrasives, the operator should walk slowly, improving the effectiveness of the cut. With finer abrasives, speed should be increased, thereby reducing the intensity of the sanding. Take care to ensure an even speed to prevent variations appearing on the timber.
Some machines have a feature which enables the user to alter the pressure of the sanding face on the timber. This can prove to be very useful, maximum pressure being used to increase the cutting power with coarse abrasives. The weight should be reduced when using fine abrasives, as these are working to reduce the marks from the previous sandings rather than removing further amounts of timber.
An edge sander will be required for most floor sanding jobs. Naturally the same grades of abrasives should be used with the edger as are used on the rest of the floor to ensure the timber is sanded to the same degree. Any differences in the sanding process will create differences in the surface of the timber. This can affect the degree of absorption of a seal into the timber, resulting in distinct colour variation between edges and the main floor area.
The importance of having the edge sander correctly adjusted has already been mentioned but the method of use is equally relevant. The edge sander should be used with just its own weight. No additional force should be applied to try and sand harder, otherwise deep circular gouges can be made - which may be extremely difficult to remove.
The edger in operation should be moved in a circular motion corresponding to the rotational direction of the sanding disc. The machine should be moved along the edge of the room briskly to avoid excessive sanding in odd areas. As with the larger machines, the edger should not be started or stopped when in contact with the floor.
Sometimes, although the same abrasives have been used on both edge and main sanding, variation can exist due to the different actions of the machines. Drum and belt sanders have a heavy, rolling action whereas edge sanders have a light, high speed, rotary action. This influences the timber fibres in different ways, which may impact on the final appearance of the floor.
Unfortunately, it may be undetectable until the first coat of seal is applied to the floor, where colour variation may be evident. To the contractor this can be incredibly frustrating, as to correct this effect the floor will require sanding back to bare wood. This situation can be avoided by employing a fine finishing system.