Looking for advice on proper mortar ro be used for thinner dry stack stone.behind a wood stove. My plan was to put durarock behind the stove and mud the stone right to that. The stone i bought called for a polymer modified mortar but all i could find at lowes was latex modified mortar which is what the guy from lowes told me i needed? Any thoughts? The wall is about 4.5 ft wide by 8 ft tall.