One of the most important steps in gunite or concrete swimming pool construction is selecting the right type of waterproofing. Concrete is a porous substrate prone to water penetration; therefore, it has to be sealed to keep water in the pool, in addition to keeping ground water out, which is often forgotten.
Every single swimming pool or water feature must be waterproofed in one way or another. Sometimes these structures present challenges and are often tricky to waterproof due to the various penetrations included in the design to accommodate elements such as lighting, piping and drainage.
There are several products on the market today for waterproofing swimming pools. Before any final decisions are made, the following information will help make material selection easier and success rates higher.
Cementitious coating and waterproof barrier products tend to bond better to concrete substrates because they are similar in chemical composition and enhanced by polymer bonding agents. These products also allow various finishing options; plaster, overlays and adhesives attach better to cementitious substrates, as opposed to a pure polymer waterproof coating.
When dealing with new pool construction, cementitious coatings are not susceptible to failure from moisture vapour transmission (MVT), which is the rate at which water vapour passes through a material at a specified temperature and relative humidity. These coatings are breathable, so they can be applied just days after pouring the concrete or placing the gunite, which leads to faster turn around times. In comparison, pure polymer systems require the concrete to cure for a minimum of 28 days to prevent failure from MVT.
In swimming pool restoration cases, it is usually difficult to completely dry the substrate before waterproofing is applied. Pure polymer coating systems cannot be applied to substrates that are not completely dry, whereas cementitious products are moisture tolerant. In fact, many manufacturers even require pre-wetting the substrate prior to application.