Just did one last week and used large flat washers behind each lag bolt.


Had to chisel out one of the stones so I could run the electrical and cabling first, which allowed for determining what was behind the stone. Lucky for me this one was plywood, but I have seen the stone (both real and faux) on OSB and sheetrock.


I've used metal pipe to sleeve the lags, but using washers seems to work equally well if not better.


Hint: Measure for the stack of washers, stack them up and then use some tape to hold them together to make it easier to put them into position. Remove tape after they're in position and do some paint touch up if they show at all.