Step 3 · Cut the Backer Board

This is the step people usually slow down on. Go finger-tight first, then a quarter turn. No rush — replay the clip whenever it helps.

Before installing the wall backer board, it's easiest to cut the opening for the niche. Lay the board on a flat work surface. Transfer the cut-line measurements you marked on the framing onto the backer board panel. Put on your safety glasses and dust mask. Use a sharp utility knife to score the cut lines multiple times. For waterproof foam boards like Kerdi-Board, you can often cut all the way through with the knife. For tougher boards or cleaner cuts, an oscillating multi-tool or a jigsaw works very well. After cutting, do a quick test fit by inserting the niche into the hole to ensure it fits snugly without being forced.