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