"harry" wrote:

The secret is in an even bed of cement and plenty of plasticiser in the
mix.
You can get a special tool that lays an even cement bed. eg

https://www.youtube.com/watch?v=9tBJyn_-Bns

I like the look of that and if I were planning to do much more, I'd get one.
But I rather suspect that the core secret is in getting the right mix of
mortar in the first place, something I always find difficult for some
reason.