Tile on existing mortar bed OK?

[polly ring]

Hello everyone,
I am about to tile the remodel bath. The previous tiles were set on a mortar bed. During demolition, the old tiles came up relatively easy, as the result, the mortar bed is still in good shape. My questions are;

1. Can I use this old mortar bed to set the new 12" x 12" cermaic tiles?

2. If YES - as you can imagine, the bed now is pretty dusty and topped with various particles/dirt. I can shop vac everything up, but im afraid I will never be able to get it perfect. How "clean" and dust free does the mortar bed have to be before i lay down the thin set and begin tiling?

Once again,
Thank you for everyone's help.
Polly

[tileguytodd]

Sand particles etc arent really a problem.Shop vac it and skim coat it with thinset to fill little voids etc.This will also kep it from creating additional divits while you try to set the tile.
Let the skimcoat dry overnight then do your layout and set those rocks

[Rd Tile]

Is it flat, or any old thinset in the way of the new tile.

The slab HAS to be clean, no dirt, dust or anything on it, vacumn, then sponge clean it.

[polly ring]

Will do. It may be a pain to get it really really clean, but I will do my best. Thank you all your guys' help.

Polly