I have a green porcelain slate floor in my kitchen. It shows dirt really badly. I used an iRobot Scooba on it. Love my robot but it took the sheen off. So I went to Home Depot and the guy said that Rejuvenate Floor Sealer would do a fantastic job. Said it was like Mop N Glo but would last longer. I cleaned the floor, used Rejuvenate and it did look better with a little shine. However, after about 2 Scooba washings the sheen is gone. Any suggestions for an enviromentally friendly porcelain tile sealer with a sheen that is safe for use with the Scooba that won't remove the sheen for at least a couple of months?

I started on this project in June 2003 when I bought my house. I have been doing a little work here and there and finally at the point where all the old stuff is gone out of the bathroom. My bathroom is a 1970's style master bath that is 8'x4'4". I pulled up the old tile, which was mortared to a 5mm(1/8") luan sheet. Then there was another 1/2" built up floor which had some dry rott areas that I removed. And underneath all of this was my original 1/2" subfloor which is undamaged. Will I need to rebuild this subfloor with 1/2" plywood and then lay 1/4" of thinset, then 1/4" tile backerboard, then 1/4" thinset, and then finally my tiles? Or is it fine to just get 1/2" durarock/tilebacker board, 1/4" thin set and then my tile? I was told to thinset under the backer board due to the warranty on the product.