The white veins in the black marble floor in my customer’s bathroom appear to be crumbling and disintegrating. What’s causing this, and can it be repaired?

Black marble, especially Negro marquina, is very susceptible to spalling. Spalling is a condition in which the stone flakes off and falls apart. Several factors can cause spalling: excess moisture, choice of setting material and method, the polishing process, etc. If the spalling is not severe, it may be possible to repair it by filling the missing veins with a polyester fill.

This floor will have to be ground and filled with a polyester fill. The filling should be done just after the initial grind and the floor should be allowed to dry throughly.