Laying new tiles over old can provide a quick solution to decorating, providing that the old tiles are flat and firm to the base. Fix any loose tiles with tile adhesive and repair any cracks in the old tiles with grout before laying the new tiles. You can also replace damaged 6-inch tiles with cheap white 6-inch tiles as a base for the new tiles to go on top. However, it is not advisable to lay heavy or thick tiles over an existing tile base.
Repair and replace any broken tiles by chiselling out the old tile. If the surface comes away from the wall with the tile, use a ready mix cement or plaster to make the surface even and allow to dry for one day. Replace the old broken tile with a new tile using tile adhesive.
Apply grout to repair any large gaps or cracks in the old tile base and allow to dry for at least 24 hours. Thoroughly clean all the old tiles with soapy water to remove all traces of grease and dirt.
Lay out the new tiles on a flat surface to work out any patterns. Tiling should start at one corner, but stagger the joints when you lay the new tiles over old ones.
Cover the old tiles evenly with adhesive using a spreader, working upward in small sections. Press the new tiles in place over the adhesive and add spacers as you go.
Mark any awkward shapes on the tiles and cut out using the tile cutter. For areas difficult to get at, it may be easier to spread the adhesive on small cut tiles than on the wall. Wipe off any excess adhesive from the front of the tiles as you go.
Allow the tiles to dry out thoroughly overnight.
Cover all the tile gaps with grout, using the grout spreader. Ensure that all the joints get a good coverage and smooth the surface using a dowel. Remove all excess grout with a wet sponge. Once dry, wipe again with a dry, soft cloth.
Always wear rubber gloves when using adhesive and grout as they can irritate the skin. If you want to tile above a partly tiled wall, use a tile border above the old tiles and continue to tile straight onto the wall above it. The difference in thickness of the tiles will then be minimised.
Turn off electrical power when working around plug and light switches. Avoid laying very heavy new tiles over old ones as this may weaken the backing and cause the tiles to fall off the wall. Avoid using extra thick tiles on top of old ones as you may find they are too thick when it comes to door or window frames. Take care when cutting tiles as the edges and cutter can be sharp.