First, drain your pool so the water level is below your installation line and at a level that you are happy to stand in. If you are tiling the entire pool or the pool floor, or just don’t want to stand in water while you work, you can drain all the water entirely.
Clean the surface you are going to install your tiles on using warm water and ordinary dish soap. This ensures that all chemicals, dirt and other contaminants are gone from the surface. Dry thoroughly with a towel or leave for a few hours to dry naturally.
Now spread cement paste over an area no larger than 4-5 square feet at a time. You can use a notched towel which will leave ridged in the paste so the tiles stick to it better. Make sure you are using tiles and grout which are approved for application in swimming pools, as not all products are guaranteed waterproof.
Now firmly push your pool tiles into place in the cemented area. The reason you work in small areas is so that the adhesive doesn’t dry out before you can put the tiles onto it. If you do end up with some dry patches, make sure you scrape off the old adhesive with the edge of your trowel before you apply a new layer, or you will get an uneven finish. If you want to keep a very uniform edge to your tiling, temporarily screw up a wooden board at the bottom of each tile row to use as a guide for sitting tiles at the same level.
If you need to cut any tiles for edges or smaller areas use a proper tile cutter to minimise waste from breakages. Draw a pencil line on the back of the tile where it needs resizing and then slice that line with the cutter. If you are using thin enough tiles, you can even score the line with a sharp knife and then just snap the tile along it.
Keep applying adhesive and laying tiles until everything is covered. Remember to work in small areas. Once you’re done, leave everything alone for at least 48 hours so the tile adhesive has time to dry fully.
Now apply your waterproof grout to the joints in between the pool tiles. Spread across the entire surface using a grout float and use a smaller implement like a teaspoon handle to force the grout into the joints. Don’t leave gaps or spaces anywhere as this will mean water leakage once the pool is refilled, which will ruin the whole installation!
Wipe away all the excess grout from the surface of the tiles using a damp sponge. Allow to dry for at least another 48 hours and then you can refill the pool and enjoy your lovely new swimming area.