The term green marble can be a bit misleading, particularly to DIY homeowners hoping to install their tile themselves. While it’s called marble, and it does have a high calcium content that makes it similar in many ways to other marbles, green marble is radically different in both makeup and installation methods.
Green marble gets its color from a mineral called serpentine. Serpentine gets its name because it spalls – or splits and flakes – in a pattern that resembles the look of a snake’s scales. This spalling becomes extremely apparent when the stone has been subjected to large amounts of water or moisture.
When most marble tiles are installed, they are put in using a Portland cement based mortar, or thinset. This thinset can be mixed with latex, but is usually mixed up with water just before setting the tile. Normal marble absorbs some of this moisture while the thinset cures, which may make the marble look darker or deeper in color for a few days to a few weeks as it dries. In the case of a serpentine marble, however, the absorption of the water or moisture from the thinset could cause the marble to begin to spall or flake, peel, and pit on its surface, even if it has been sealed against moisture after installation.
To avoid this, serpentine marbles should always be installed using an epoxy-based mortar, rather than a traditional Portland cement-based mortar. This will ensure that the marble does not absorb any moisture from the setting material, causing an installation failure before it’s even finished.
Before grouting any serpentine marbles, the surface should always be protected with an impregnating sealer to both prevent the grout from staining the marble and to prevent any moisture from the grout from causing the serpentine to spall.
Serpentine marbles are often much hardier and more durable than other marbles, making them an excellent choice for many applications. Be sure to install them with the correct materials and procedure to ensure they live up to their potential.