A sealer would be good to stop staining however bleach or a marble cleaner can be used to remove stains.
Polyurethane on marble table.
I purchase a marble topped coffee table for 5 because someone put polyurethane over the marble so it wouldn t chip.
Your question was can i put polyurethane on marble i answered this question.
Dip your brush gently and take your time painting the surface.
I would use a product called soy gel.
Turn an old table into a marble master piece with just some simple steps some paint and sticky back vinyl.
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.
Let the polyurethane sit for about 10 minutes after stirring to allow the foam to settle.
Use a sealer made to seal marble.
Polyurethane tends to gum up sandpaper so use paper or pads that resists clogging 320 grit.
Allow the polyurethane to dry two to three hours.
The table is going to be my new desk but at the m.
I m sorry there isn t a cheap easy fix for your problem but i not only answered your.
Dip a paintbrush into the gloss polyurethane varnish and apply an even coat from one end to the other using long straight strokes.
Polyurethane products especially water based ones tend to foam when you agitate them.
You can get from here.
When a drop of water soaks into the marble and doesn t bead up it s time to seal.
A quick hand sanding between coats flattens our flaws before the next coat.
Clean off the white stuff.
The marble is less likely to scratch as is why it is used as a cutting board surface.
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.
Poly will scratch and flake off looking worse than a few scratches in the stone.
I also told you the only viable fix for your problem.
Apply a second coat if you desire.
Best to stay away from poly for this purpose.
The foam forms bubbles on the surface and if they harden they can be difficult to camouflage.
So in my opinion i would not use polyurethane on your marble top.