Costlier epoxy thinsets, which also must be mixed on site, blend a liquid resin and hardener either with sand and portland cement or with a silica filler. In residential construction, epoxy thinsets are used mostly with green marble, which can warp if installed with water-based thinsets. Mastics can be used straight from the can . Unlike thinset adhesive, mastics don't need any mixing. But they do not provide the same bond strength or water resistance as thinset.
Mastics are sticky adhesives that consist of a bonding agent and a carrier.
It evaporates as the mastic cures. Open the bucket, stir the glue if it appears to need it, and you're ready to trowel. Mastics also can cost a bit less than thinsets. But you can't beat the versatility and long-term performance of thinset adhesives. As a group, thinsets stick to most substrates, including mortar setting beds, concrete slabs, tile backerboards, drywall, plywood and even existing tile or plastic laminate.