Although it is possible that your table has a polyurethane or varnish finish it s much more likely that the marble was polished to a high gloss that has become scratched and dull.
Can you seal marble with polyurethane.
Ok this is my question i bought marble tiles that has this polyurethane clear coat over that makes it look really shiny.
It will penetrate the surface and protect it.
Your question was can i put polyurethane on marble i answered this question.
The shine most likely will not last and and when it begins to break down it will look very bad.
I don t want or expect an accept that is followed with negative feedback.
Also keep in mind that the sealer is intended to fill the pores and coat the exposed minerals in the stone not to coat the surface.
If residual sealer is not completely removed from the surface of stone it may cause problems including a haze on the stone s surface that may develop.
So in my opinion i would not use polyurethane on your marble top.
Use a sealer made to seal marble.
I also told you the only viable fix for your problem.
Oil based polyurethane for countertops.
Polyurethane varnish is one of the best finishes for a countertop it s durable and when applied properly can be just as subtle as lacquer.
The installer says i can t apply a sealer because it wont penetrate in the stone because of the polyurethane clear coat that has on it but the previous estimater that came to me house says that they will goin to seal the marble i call floor and decor where i bought the.