I plan to install tile on a Formica countertop with 1/4” cement backer board. Do I need to apply thin-set mortar between the backer board and Formica to stick it down?– John
I would both glue and screw the cement backer board down to the plastic laminate countertop, using either thin set or construction adhesive, before laying the tile. This will make the backer board more rigid, and prevent the tile from cracking or coming loose.
Gluing the backer board to the countertop is particularly important when using 1/4” thick cement backer board, since it’s more flexible than 1/2” backer board.
Good luck with your project,