Mortar Mix for slate coping

[BobbyBrown]

Hi all,

I've had a wall built in my garden with some slate coping to finish it off. Unfortunately in the past 18 months this has all come loose and the builder has already replaced it but it again wobbles. I've added a drip groove to the underside of the coping as I think this might have been weakening the mortar. My question is what mortar mix / additive would you suggest for fixing it once and for all?

 

[joe-90]

Grey waterproof tile adhesive. You need to prime the slates too to get rid of the dust.

 

[BobbyBrown]

Thanks for the tip, just tile adhesive or would you mix some in with a standard mortar mix?