Sorry for the long delay took some time to sort this out
OK first off mixing the ad mix to the thin set I have should not have been an issue.
2nd I did not back butter all of them because after the first few and what appeared to be a solid bond when I had to use the trowel to lift the first few I did not feel it was necessary. I maybe wrong but read on
What did happen is the lot that the thin set came from was recalled for insufficient cement in the mix. Home Depot never took this pallet out and instead sold most of it apparently before the complaints came rolling in. Home Depot was very nice at refunding the $12.59 since I still had the receipt ( whoopee for them they just lost a return customer)
What I then had to do was pull up all the tiles and grind the surface which I did with a lot of work and a grinder and a sonic tool I had. (Ouch my knees) I then applied a floor leveler to take care of any of the gouges (I was careful But) and then reapplied the red guard over the floor. I then went to the tile place I mentioned and bought thin set and re applied it I first put down a thin coat with a 8" wide putty knife and then troweled it on with the notch trowel. Oh yes not ad mix to this bad they solid me the right product for the slate. then I started laying the tile which I also cleaned off with a wire brush on the grinder. Now the only tiles I back buttered were the edge and the wall tiles to make sure I had no voids in this area. I then put three coats of sealer on after the thin set dried then grouted. Easiest grout job I have ever done Grout also from Tile Store. Then 2 coats of high gloss sealer over the top after 3 days of dry on the grout.
It came out perfectly and is is water resistant the water beads right up no penetration what so ever the tile guys at the tile store suggest a re-coat every 2 years and it should remain water resistant. One other thing I wanted to mention the redguard although expensive went on like a dream I used a brush not a roller to help assure a nice think coat and it cut the time and work substantially and I really liked working with it even when laying the tile. I will send pictures as soon as we are done with all the fixtures.
But this was a bigger project then I expected thanks to my taking the convenient route and trying to make one trip at HD Never Again.
Thanks for all the advise lets hope this lasts till I resell it. 4-5 years