My friend just put stone tile on his fireplace. I know that to install it you need to skim coat the mess, dry overnight, then butter back the stone to the wall, and grout. My friend DID NOT skim coat but instead added some kind of bonding agent to the mortar($6.00 bottle to 6 bags of mortar), then butter backed to tile to the mess, and grouted. He says this is just as good and will last just as long. I say its not because the mortar doesn't necessarily stick to the mess but wraps around it to carry the weight then wet mortar bonds to dry mortar. Is this method just as strong and will it last just as long?