Restoring terrazzo's beauty: How stubborn is the stain

Q. What is the correct way to clean and polish a terrazzo floor darkened by a polyurethane product? The floor has been lightly sanded after other means failed to remove the stuff. It now looks slightly mottled. What should I do?

Shirley Stille, Valley Stream, N.Y.

A. One expert in the field comments that terrazzo, thought durable and beautiful when properly maintained, may become almost impossible to restore to its original beauty when stained. If the stain is the result of polyurethane, the manufacturer's directions for its removal should be carefully followed.

We wonder if the floor was stained by something that penetrated the grout of the terrazzo before it was sealed. Is this possible?

The seal should come off with the use of the right solvent and would leave any grout stain more obvious than before stripping. If so, alas, the stain may be permanent.

A household bleach applied to a very small area might considerably lighten the stain, depending on its type and the grout color.

Another possibility is to reseal the terrazzo with a finish that matches the stain, if that is possible. This method might not work on an extremely light-colored terrazzo and might result in a yellowish cast. On a darker terrazzo, resealing might work quite well. Resealing could diminish the contrast between the stain and the unsealed grout. Experiment in a small area.

Sanding the terrazzo scratches its stone chips, making them appear dusty rather than having the sheen of highly polished and sealed terrazzo. Resealing should eliminate the dusting and deepen the color tone of the chips, thus distracting the eye from beholding the stain.

Proper sealing and maintenance of terrazzo is an absolute necessity to keep it free of stains and looking its best.

Were it mine, I'd run the stain problem by the manufacturer of the terrazzo for verification of the above opinions. Then follow its recommendation to the dot.