If its a clean break you need a white 2 part resin (tenax), colour match using water colour paint (in a tube)....only a tiny bit is required.....paynes grey is a good starting point as the marble won't be as white as the resin.
Once colour matched add the hardener and spread very thinly along the joint , push together and clamp if possible keeping the top level.
Gently scrape excess glue from the top and edges with a razor blade and wipe clean with a solvent on a clean cloth.
The joint will be delicate and care should be taken moving the top when fixed.....it should really be dowelled or pinned but that gets more complicated!!
DirectStone, October 2009
