In my opinion, high quality exterior grade 1/2 inch plywood or 3/8
inch 5 ply plywood is probably not much heavier than 1/4 inch
masonite and much stronger and more reliable. My suggestion is to
drill about two 3/8 inch holes in whatever backing is used behind
each tile for the glue to go in and form a penetrating rivet hanger.
When putting the tile down, I would butter some fresh construction
adhesive, tile mastic, or thin set mortar with a putty knife, tiling
trowel, or caulking gun on both the back of the tile and the backing
board. I have best long-term durability with latex enhanced thin-set
mortar available as dry powder at the tile department of building
supply places. Be careful not to mix it too thin. It should be used
at least as thick as smooth peanut butter. It is fairly strong
overnight, but continues to get strength for 8 weeks or so.
It is good to make a sample at the same time with the same adhesive
with a piece of similarly fired clay on a scrap of wood to test the
drying strength prior to hanging the panels.
I like to roughen the tile backs with deep scratches as I make them
so they bond better to whatever adhesive is holding them.
I dread call-backs to replace tile that has dropped on the floor and
broken. I avoid epoxy for this because it has failed me several
times. It is fussy about how it is mixed, temperatures, etc.
for tile installation pictures