Quarry tile adhesive outdoors

Just built a doorstep over Easter and want to finish the job with some nice quarry tiles. The step finish at present is mortar and I'm unsure what to use to fix the tiles with.
What would be best bearing in mind that the surface to be tiled onto is somewhat undulating so will need to be approx 7-10mm bed?
A) An exterior floor tile adhesive and grout B) A mortar mix like I've used in the step construction
Cheers,
Dave
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Tony B wrote:

there is little diffrence between em.
quality tile cements seem to be cement, fine sand, and a plasticiser or maybe a more organic filler. I'd use playpit sand and cement meself, mixed strong and stiff.

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Whatever you do, make sure that there is a slight slope so that a pool of water doesn't collect on a step. Use a level very carefully. I've just seen a very expensive tiling job where a pool of water collects right where people will walk.
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