QUESTION

Do Not Install over Plywood for Exterior Use - Call I Install Tile over Plywood for Exterior Use - I am looking for an adhesive for an outdoor red clay mural we are making at our school. The flat clay figures have been kiln fired. They will be attached to plywood. The school is on the CA Central Coast. The temperatures range from low 30's to low 90's. Thank you for any help you can give us. We made one mural several years ago using mastic and some pieces have fallen off.
Thank you!

ANSWER

ANSWER - First of all you should not be installing the clay tiles to plywood if it is going to be used outdoors.  Plywood is moisture sensitive and will expand and contract leading to warpage and tiles falling off.  Using mastic compounds the problem because mastic is not a long lasting adhesive.

You should use a cementitious backer board for attaching the clay figures.  You can buy them at Home Depot or Lowe's or any tile store.  The common size is 3' x 5', but there are larger sizes, and it comes in 1/4" thin or 1/2" thick.

Normally a thin-set mortar is used to bond the clay tiles to the cementitious board.  If the clay tiles are porcelain then you need to use an ANSI A118.4 modified thin-set mortar that provides better bonding for the impervious porcelain clay.

Good Luck!