Green Marble Curling
There are a handful of marbles that are more susceptible to moisture and hysteresis. Green marble called Serpentine is one of these, and the tile may curl, warp and cup when set with a mixture of Portland cement and water or mastics.
When specifying stone, always check with the stone supplier for recommended setting materials. When water enters the stone, it causes the marble to release any internal stress, causing it to warp. Warped green marble can easily be avoided by using the correct thinset, void of water. This thinnest is called Epoxy.
Epoxy thinset (or mortar) is a mixture of epoxy resins, epoxy hardener, and sand that are used for green marbles. Since epoxy thinsets are 100% solids, they contain no water.
The below visual shows a technical gauge of what happens when these specific stones take on moisture, commonly referred to as dimensional instability.
Image source: Tile Magazine, Technical Focus