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2nd floor underlayment:

by Vic
(Monterey, CA)

Q. I'm laying stone on an elevated wood patio and don't want water to seep through. I have a 2X6 butted floor on 16" centered joists and plan to cover that with 3/4" plywood. I'm planning on 1" flag stone above that. Should I use a polyurethane barrier with wire mesh glued on top (no nail holes)to hold the mortar?

A. Wire mesh has too much spacing to hold down a bed of mortar. The ideal method is too tape along the plywood seams. Then staple galvanized lath to the plywood and apply a heavy coat of a waterproofing sealer. Make sure the sealer drys completely before laying the mortar.