I would use a product called soy gel.
Polyurethane on marble table.
On shaped edges use synthetic steel wool such as scotch brite pads labeled very fine tabletop finishing.
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.
Clean off the white stuff.
The marble is less likely to scratch as is why it is used as a cutting board surface.
I m sorry there isn t a cheap easy fix for your problem but i not only answered your.
Let the polyurethane sit for about 10 minutes after stirring to allow the foam to settle.
Dip your brush gently and take your time painting the surface.
I purchase a marble topped coffee table for 5 because someone put polyurethane over the marble so it wouldn t chip.
The shine most likely will not last and and when it begins to break down it will look very bad.
Use a sealer made to seal marble.
It will penetrate the surface and protect it.
You can get from here.
Dip a paintbrush into the gloss polyurethane varnish and apply an even coat from one end to the other using long straight strokes.
Turn an old table into a marble master piece with just some simple steps some paint and sticky back vinyl.
The table is going to be my new desk but at the m.
Your question was can i put polyurethane on marble i answered this question.
Watch as rachelle from originally worn attempts and slightly fails to finish a table top with annie sloan graphite unicorn spit polyurethane.
A quick hand sanding between coats flattens our flaws before the next coat.
Best to stay away from poly for this purpose.
I want to remove it but not sure how.
Polyurethane products especially water based ones tend to foam when you agitate them.
Allow the polyurethane to dry two to three hours.
A sealer would be good to stop staining however bleach or a marble cleaner can be used to remove stains.
Apply a second coat if you desire.
Poly will scratch and flake off looking worse than a few scratches in the stone.
Polyurethane tends to gum up sandpaper so use paper or pads that resists clogging 320 grit.
When a drop of water soaks into the marble and doesn t bead up it s time to seal.