Hi - my front doorstep has 15mm x 15mm quarry tiles exposed to the elements. Some are now cracked and I am going to order some replacements. I was going to set them in using quick drying waterproof cement (Cementone). However I wonder if I need to use specific tile grouting. perhaps I need cement to bed underneath the tiles with grouting round the sides. I have used the cement before on paving slabs and the colour seems to be about right. I would be grateful for any advise please. Thanks.