QUESTION

Can I use mastic on kitchen back splashes and also on accent tiles in showers . Accent tiles are approx 5 - 5 1/2 ft above floor .
Thank you

ANSWER

ANSWER - There is a type 1 and a type 2 organic mastic.  Type 1 mastic is more water resistant, but only suitable for limited water exposure.

Using the mastic on the kitchen backsplash is probably ok, but in a shower it depends on how much water exposure it will get and the substrate that it will be attached to.  It is better to use a cementitous thin-set mortar over cementitous substrates.