When waterproofing under tiles there are many factors to consider. You may be pondering what ceramic tile adhesive or smoothing cement to use over a waterproof membrane. Your answer lies partly in the type of membrane used, and partly in the adhesive characteristics.
There are a number of different types of membranes on the market with very different chemical and physical properties. As a result, tile adhesives have varying performance on each of these materials.
Here we discuss the properties of two popular types of undertile waterproofing membranes.
Acrylic membranes are the most common and are water based. The polymer base is a modified acrylic material and can be one or two part. These membranes are flexible and have a low, non-toxic odour.
These membranes are normally compatible with tile adhesives based on cement, which dry by hydration of the cement. The use of premixed adhesives which dry by evaporation is not recommended as water cannot escape, especially where non-porous tiles are used. In this instance, the adhesive remains soft and tiles may come loose.
Polyurethane membranes can be rigid or elastomeric (flexible). The rigid types are rarely encountered in tiling situations, so let's look at the elastomeric variety. There are three basic types of elastomeric polyurethane membrane.
The first type is where the organic molecules in the polymer systems react to form a continuous cross-linked membrane. The second type of polyurethane membrane is a solvent-based system that relies on a moisture cure. Typically the first and second types listed here cure very smooth and cannot form proper mechanical bond with a tile adhesive. Each also tends to be low in tensile strength — barely passing the Australian and New Zealand standards.
The third type of polyurethane membrane is a waterborne solution which can retain the high performance of a polyurethane membrane, but also provides a surface which is compatible with cement-based tile adhesives. This third type should be the preferred undertile polyurethane option.
Whatever the situation with your tiling project, keep in mind that all ARDEX membranes and tile adhesives are tested to work together as a system, giving a reliable result every time when used in tandem.