It is one hundred percent possible to tile over a waterproof membrane.
Not only is it possible, however, but it is also safe to do so. It is a common practice nowadays to install a waterproof membrane before tiling.
This is especially true in cases such as showers.
When installing tiles over a waterproof membrane, it is recommended that you use the thinnest mortar that you can mix yourself.
This mortar is often of a higher quality than the pre-mixed kinds of mortars available.
Having a waterproof membrane or a waterproof backer board underneath tiles installed in a bath or shower room is an absolute must.
Having this waterproofing under your tiles will protect your wall and tiles from water seeping through.
Although it is optional, it is also recommended that a waterproof membrane be installed underneath regular floor tiles too.
Tiling over a liquid waterproofing membrane in a shower is not an excessively difficult thing to do.
Here is how you do it:
1. Prepare the Surface
The first step in this simple process is to prepare the surface for the waterproof membrane.
To do this, you will first need to have a waterproof backing board installed.
The waterproof backing board needs to be sealed at the joints with a thin adhesive and mesh tape.
It is not recommended that you use a joint compound and paper tape when sealing joints in a shower.
These will likely be destroyed by the water.
When the waterproof backing boards are ready, you will need to ensure that the area where the waterproof membrane is going to be applied is spotless.
Remove all forms of debris in and around the area and make sure it is completely clean.
The area may need to be scraped, vacuumed, and washed to prepare it to accommodate the waterproof membrane.
2. Paint on Waterproof Membrane
Once the area is clear and cleaned and prepped, it is time to begin the process of waterproofing the surface by applying the waterproof membrane.
Depending on the type of waterproof membrane you have, you should be able to simply paint on the waterproof membrane.
It is recommended that you use a paint roller to apply the waterproofing membrane.
Use smooth, even strokes to apply the waterproofing membrane.
It is best to overlap strokes to get proper and full coverage.
Make sure you are maintaining an even application throughout the area.
In some areas, such as corners, it may be necessary to make use of a paintbrush to get into the area properly.
After you have painted on the waterproof membrane, you will need to allow it time to dry.
A minimum of three hours of drying time is recommended.
The waterproof membrane may take longer to dry in cold weather, however.
3. Mix the Mortar
After the waterproof membrane has been allowed an adequate amount of time to dry, you can begin the process of the tile installation.
Firstly, you will need to mix the mortar.
It is best to use the thinnest powdered mortar.
The mortars that you have to mix yourself are usually better quality than pre-mixed mortars.
High-quality mortar is also more likely to bond better with the waterproof membrane.
This will result in a longer-lasting tile installation.
Mix your powdered mortar with cool water until it resembles the consistency of a cake batter.
Ensure that it is thin enough to spread easily, though.
4. Spread the Mortar
With the use of a notched trowel, spread your mixed mortar over a small area of about two feet by two feet.
It is recommended that you apply enough mortar for one tile at a time, rather than apply all the mortar.
Apply large areas of mortar at a time may result in it drying before you install the tile.
This will then lead to the tile not adhering properly to the mortar.
5. Install the Tiles
Once you have laid the mortar, install the tile by pressing it into place.
Be sure to press on the tile firmly enough so that the mortar spread underneath and adheres the tile to the surface.
Do not press too hard, however, so that you break the tile.
It is best to make use of tile spacers to keep tiles spaced evenly.
Repeat steps 4 and 5 as needed to tile the entire surface.
Some tiles may need to be cut to fit into corners or smaller spaces.
Remember to remove the tile spacers before you grout and seal your tiles.
It is possible to waterproof over tiles, however, a waterproof base is still necessary.
You can apply a waterproof seal over tiles, but it does not have the same effect as a waterproof base.
Waterproof bases are essential in certain areas and cannot be replaced by a top layering of a waterproof coating.
It is perfectly acceptable to tile over a waterproof membrane, the trick is to do it the right way.
Once done, it is difficult to correct.
Get it right the first time and the results will be great.