This is one of the most common problems flooring contractors encounter and the cause of many complaints from customers. The chatter marks only become visible after the finish has been applied.

There are several possible causes:

• Parts of the floor flex up and down as a heavy sanding machine passes over
• The abrasive is not tightly fitted on the belt or drum sander
• A badly balanced drum
• A shuddering movement in the sanding machine
• The abrasive is not clamped in properly around the drum and protrudes slightly
• An overlapping seam on the belt rubs against the floor – this is easy to avoid by using a belt with a flat butt joint

Practical tip: use Bona abrasive belts which have a butt joint. This means that the joint does not have a different thickness to the rest of the belt