I laid non slip tiles on a concrete door step using exterior adhesive in summer 2009. Some of the tiles came loose during the winter. I relaid the tiles which had come loose using high performance grab adhesive to see if this would be better. Unfortunately the tiles lifted again during this winter. Some neighbours who had quarry tiles also had their tiles come loose - one neighbour's however did not come loose.
Any suggestions. Should I have primed the steps before laying the tiles?