They sell spacers at the big box stores or electic supply houses, of varying thicknesses that you attach to the existing boxes like you attach an outlet or switch, to bring it flush with the new tile.
Your friend has shared a link to a Home Depot product they think you would be interested in seeing:
Those don't do anything to support the outlet (they slip inside the box).
Please tell this to all the inspectors in my area in both MD and VA.
But he's in Washington.
Agree totally - code requires them. But from a practical perspective, you'd be lining a stone wall covering with a plastic liner. I'd skip the box extender completely and just use longer screws. This would technically be a violation of the NEC. Now if it were beadboard, nickelgap, wood baseboard, or anything other combustible material, I'd absolutely use the box extension.
www.finehomebuilding.com
Wouldn’t load for me due cookies etc. Spam like.I did this and eliminated most of the holes in my backsplash.
How to Install Plug Mold Under Cabinets - Fine Homebuilding
Use plug mold in kitchens to avoid cluttering your backsplash with outlets. Mounting at a 45° angle minimizes obtrusion.
Or 1/4" copper tube.
I'm too cheap for that but I have been known to wrap #12 or #14 solid around a Phillips screwdriver to make a spacer or 12. 8/32 nuts work well as long as it only needs a couple of them.
#14 wrapped around a scratch awl, is easier they are tapered to make slipping the coil off & use dykes to cut to desired length.
