When you are retiling the floor or wall, removing the old tile adhesive may be the most difficult part of the entire project. Tile adhesive is a glue that hardens into a material that is very difficult to remove. One way to remove the adhesive is using a chisel and hammer. Start at the corner of the adhesive and work your way toward the centre of the adhesive. Once you get to the middle of where the tile was, move on to the next corner.
You can also remove the adhesive with sand paper. To do this, place ice cubes on the area to freeze the adhesive. Once it is frozen, use a rotary buffer with a sand paper disc attachment to remove the adhesive. However, you have to ensure that you don't damage the underlaying materials.
Muriatic acid is a solvent that will soften the adhesive. Dilute the muriatic acid by mixing equal parts of muriatic acid and water. Use an old rag to apply it to the adhesive only, as it can damage other substances. Make sure that you wear rubber gloves when doing this. Let the mixture soak for 15 minutes. Once the adhesive is softened, you should be able to remove it with a putty knife.
Using an adhesive remover is another option. These work in much the same way as muriatic acid. However, these solvents aren't as damaging to other materials. If you are environmentally-conscious, opt for a citrus-based or soy-based remover, as these are less toxic. Some of these are available in a paste and others are liquid. The type you choose depends on the location of the adhesive. Liquid works better for floors, while paste is ideal for walls. To use these, simply apply the remover to the adhesive using a towel. Allow it to set anywhere from thirty minutes to overnight, depending on the directions on the remover. Then, use a putty knife to remove the adhesive.