Most ceramic tile adhesives are supplied ready-mixed, although a few types will need to be mixed with water. These have a limited life and you should only mix up as much as you can apply in a given time. While your surface should always be as smooth and level as possible, there are thick bed adhesives available, which will help even out some irregularities. Be warned: these are a little more difficult to apply. A can of 5 litre thin bed adhesive will cover an area of roughly 4 m sq (a little under 5sq yds). It should be laid on in sections or areas of about 1m sq (1 sq yd) with the notched trowel or spreader 3mm (1/8in) thick.
Step by Step Instructions
1 Arrange battens
Nail a horizontal batten to the wall with the top edge one tile height above the lowest point to be tiled, then nail a vertical batten at the edge of the area. Check them with a spirit level.
2 Apply adhesive
Using a notched plastic spreader or a notched trowel, apply the adhesive to cover 1m sq. (lsq.yd). Use the notches to form horizontal ridges of the correct depth (about 3mm or 1/8in deep).