I am installing my own granite tile countertop and backsplash in new construction. I planned on using 3/4" plywood and hardi-backer for the countertops, what about the backsplash? We've used OSB throughout the rest of the kitchen as substrate for the knotty pine planks. Can we use this on the walls under the hardi-backer, or should we switch to ply?

Thanks a lot!

I would add a second layer of plywood to the countertop. Granite needs a more stable base than ceramic or porcelain do and the cement board wont provide any structural strength. On floors we base the required support off of 16" on center joists. With a countertop you have wider spans, like over a dishwasher where the span could be 2 feet to 30 inches of unsupported substrate across and obout 2 feet from front to back.

quote:

Originally posted by Tileguybob:
I would add a second layer of plywood to the countertop.

Thank you. I've wondered about that. I assume you'd find the OSB satisfactory under the Hardi on the backsplash?

I would not use OSB at all. Use a good quality Plywood exterior grade board. OSB has the tendency to swell when it gets damp.

Also just a question. Why would you put down plywood at all on the top. Or the backsplash at all? Is it just for strength or something to nail wire mesh onto?

We have used (are using, actually) OSB as an overlay on the studs to give better attachment for the knotty pine beaded planking we're using on the walls and ceiling. So, to keep wall thickness consistent, and give solid backing to the vertical hardie backer for the backsplash, we were thinking of using it...although we'll probably go to ply now that we think of the swell factor if something happens at the juncture of countertop and backsplash.

quote:

Originally posted by AnnainOK:
[QUOTE]Originally posted by Tileguybob:
I would add a second layer of plywood to the countertop.

Actually, I probably know the answer to that, and I think not...the possibility of water getting under at the joint between backsplash and counter is reasonable and swelling could occur.

So my next question, sir, is the stability of the plywood substrate increased by placing the layers at right angles to each other; and, if so, could we use two 1/2" layers to help shave some height off the countertop without sacrificing stability?

Thanks.

The joint between the counter and the backsplash should be caulked after the tile are all set. Seasonal movement and other weather related factors can cause the outside wall to shift slightly and that could create a crack in the joint if just grout were to be used. i elevate the bottom course of tile 1/8" off the countertop and get a tube of caulk made by the grout manufacturer in the same color as the grout you choose.

Changing the orientation of the upper board from the lower is an absolute necessity on floors, but not as big a deal on a counter. Two 1/2" sheets wont give your stone the support it needs over any long open spans of the cabinets. A lazy susan in the corner, the sink cutout or the area above a dishwasher are three examples of large open areas that would exhibit excessive deflection on a countertop.