I want to lay floor tiles on a concrete patio slab. The existing slab is not level. It has dips and humps. I will establish a finished grade from the highest spot. Im wondering, what is the minimum thickness for a mortar bed for ceramic tiles?

My Thai building contractor used many shipments of a mortar products from

http://www.netweber.co.uk/construction-mortar-products.html

On the back of the bags in Thai are instructions and this company has telephone and e-mail contacts in Thailand for technical advise. We used two different mortar products from Weber, one was under granite, one under ceramic tiles. One was more suitable in "wet areas" such as showers as I recall.

Interesting information here:- http://www.thetiledoctor.com/installations/fl_methods.cfm seems 1/2 - 3/4" is the minimum required.

It depends on the tile you are using as the profile at the back varies.

You should choose the size of your trowel (notched) so that there is enough mortar in contact with the tile once fixed. You can easily check it by installing one tile and then pulling it back out. If the mortar has been in contact with 75% or more of the tile surface you are ok.

If you have to lay the tiles to slope, thickness can be as much as 35mm at the start of the slope.