Whats the best/easy way to cut backer board for bathroom tile?

You can score it. You must score it deep with a cement board scoring tool (available where you bought the board), move it to a straight edge and snap it. You will probably have to cut the embedded fiberglass mesh with a utility knife, no big deal. The power saw is extremely dusty. If you're working outside, by all means use a saw, your cuts will be much cleaner (wear a dust mask). Use a masonary blade in your circular saw and you'll be O.K.

You ll be effective.. in view which you don t get that lots water up there ..The tile will safeguard it from any small moisture that does splash up there..I in simple terms propose to wipe the tile down after each and each bathe to stay away from water spots.. Sealing the grout prevents water penetrating the grout and any impurities interior the water is what stains the grout over the years.. It s not a treatment all even though it is going to help.. Caulking the sting by the fiberglass and the tile will could be performed in some unspecified time interior the destiny.. The organic expantson/ contraction and flexing will crack the grout so plan on that .. I ve performed 100s of them (mine included) and not one million call returned / concern GL

you can cut it with a skill saw and that is the best way to do it. no you can't score it and break it. I know it nasty to saw it but that is the way to do it. Been there and done that

same as dry wall. There is a special knife you can get for scoring.