Waterproofing and other significant surface preparation is hot on the lips of tile and adhesive manufacturers globally. The magnitude of failures is overwhelming, none more poignant than in Australia’s swimming pool industry. In a country so well versed in water conservation and salination of the available soil, I find it incredulous that waterproofing’s importance is not recognized by pool builders or even questioned by the end user or client.
At this point, you might wonder if this is just scare mongering? Concrete, after all, IS waterproof, isn’t it? I will come back to this later.
Pools in Australia, and by this I restrict my meaning to ‘concrete’ pools, are more often than not sprayed into a steel-reinforced lined ‘shell’. The form is either cut out of compacted soil or framed up with any number of materials–wood and corrugated iron are the most common. It is important for the ‘gunnite’ or ‘shotcrete’ to hit a solid surface as it is sprayed and pumped into position. This is a common practice in the USA, as well. Europe prefers ‘poured’ methods. This involves framing precise areas, walls and floors etc., and pumping concrete whilst vibrating it using a number of techniques. This is claimed to make the concrete both denser and therefore better, and leaves a smoother surface. There are many types of pools (fiberglass, 
stainless-steel etc.) and these all have unique waterproofing issues that I need to cover in another article.
Waterproofing a pool for ‘leaking’ is only one reason to waterproof. The average price to waterproof a pool might be between 10% and 20% of the pool cost. The cost of replenishing lost water
due to leaks are high, not only on the pocket book but in water conservation areas as well. It’s also the fact that pool water
gets into the shell and migrates throughout destroying the structural materials of your brand-new pool.
Pool water often fluctuates wildly in its pH. Even leading equipment manufacturers will have issues with their chemical control systems from time to time. Sensitive calibration plates can ‘salt’ up and give false readings. In any case, pool water is toxic to concrete–one day being acid, the next alkaline.
It’s the most aggressive environment for tile installation. This doesn’t even address the effects of pH and high temperatures on adhesives.
Waterproofing a pool solves a number of issues, including leaking and pH bounce affecting the shell for starters.
But it can also create some other mechanical issues that need to be understood. Waterproofing is very black and white: a shell is either waterproof or not. There are processes that are completely negated by the smallest pin hole in a membrane style product. Within weeks, a pool shell and render can be completely saturated, leaving an irreversible and uncorrectable problem. Stripping the surface back to the shell often the only option for repair.
At this point I need to explain something.
Waterproofing is like a seatbelt. We hope we will never need it. We don’t think, “Well, I’ve never had a car crash in 20 years of driving, I don’t need one.”
With a pool, we hope the air pockets behind the reo-chairs don’t blow, the penetrations hold and the lights (among other things) are sound. We hope the glass windows don’t leak, the cars in the garage below don’t get leaching acidified water on them, and the grass and plants don’t die in the garden.
Taking a number of equally crucial steps is required to obtain 
a satisfactory surface on which to tile and plaster. Some plasters have qualities that can maintain a watertight finish in the majority of the pool, but this usually excludes the waterline where the tile meets the plaster, also known as the number one ‘leak zone’. Waterproofing appropriately can avoid water coming ‘up’ through the shell (known as wicking) as in a river edge style pool. Hydrostatic valves are another item also required but not discussed here.
There are 3 or 4 completely different ways to waterproof a pool and some combinations of these is even more useful. It’s like having 3 seatbelts on, as with a race car–negative and positive hydrostatic issues, pH bounce and flexibility can be tackled, as well as challenging issues like north-facing vanishing edges that heat up to over 100 degrees only to have cold water run over it 100 times a day in midsummer (thermal shock membrane). Tiles don’t enjoy this, especially highly absorbent ceramic tiles which are wrongly but commonly used.
Concrete, you must understand, is like a very dense sponge. Given the chemical cocktail of pool water, you have a recipe for disaster. To hope, with fingers crossed, that the pool water will not react with the render/adhesive/shell/ grout is naive to say the least and a court may even see it as negligence.
Thankfully, having to deal with frost and below zero temperatures is not an issue in Australia. However, if it was, you can imagine the issues with water frozen whilst trapped in a concrete pool shell. I will cover this in another article, although this possibility may actually incentivize pool contractors, builders and tilers to decide to protect the shell in other ways.
Water will migrate into the shell and at the very least penetrate 1/2inch -10/15mm into it, causing the pH acid/ alkaline cycle to eat away at the concrete, tile, adhesive and grout. This likelihood increases if the water is kept at 30+ degrees, which is very normal in today’s market.
