Questions & Answers

I found a beautiful piece of 3' x 4" x 5/8" marble for the top of my curb I'm constructing out of two by four. The two by four will be sheathed with an outer layer of 1/2 inch cement board and wraped in Kurdi cloth. I need to know how much to allow for the outer layers? At first I thought it would be just the thinset under the tile but then realized it would also be wrapped with Kurdi cloth and thinset under that as well. I know it's probably one of those "It depends" questions but considering minimal overlap and a clean installation, is there a general rule of thumb you can use for estimating how much to subtract for these extra layers? I'm thinking a 1/2 inch should get me close? I'm also guessing that it will require making the underlying curb structure slightly narrower than necessary so that the final width can be adjusted with the amount of thinset under the tile?

If that's a little complicated, what I need to know is, prior to the application of any tile what should the width of my prepared curb be to accomidate a 4 inch marble cap? Assuming that the cap covers the tile edges beneath it.