05:38AM | 12/27/06
Member Since: 12/26/06
2 lifetime posts
i'm about to use some for an upstairs bathroom project and i could use some input. here is the scenario:

the current subfloor is 2 inch thick toungue and groove car decking sitiing on 4x8 inch fir beam stringers. while this car decking is the floor on the second level of the house, it's the ceiling on the first level of the house. i have concerns about applying thinset directly to the car decking, even though it is the subfloor. should i put down plywood over the car decking, apply thinset to that, then apply the hardibacker? fyi, we are putting down 11 inch porcelain tile on the hardibacker. also, hardibacker suggest 5/8 inch plywood, but if i put plywood over the car decking could i use plywood slightly thinner?

thanks in advance for any help you can provide.



04:40PM | 12/28/06
Member Since: 07/03/05
283 lifetime posts
Yes, you should put down a sheet of 1/2" to 3/4" plywood (no CDX permitted)to eliminate the transer of lateral movement in the planks up through the Hardibacker and into the tile which will cause them to crack. Screw the ply to the planking then set the Hardi in a bed of thinset and anchor with galvanized roofing nails or backerboard screws. Fill the 1/8" gap in the plywood seams with a cheap latex caulk so thinset does not ooze down into the gap. Tape the hardi seams with fiberglass mesh tape and coat with modified thinset.
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