Why do most tiled pools leak?

Introduction

I have written this short paper because many people ask us if we can build a tiled pool in our operational area in SW France and our answer is always "Yes - but it would be very costly and we do not build them"

The provocative question posed in the title of this weblog can be answered with the simple statement  "Most tiled pools leak because of faulty design and installation procedures"

Let's take look at what is required in ensuring that a tiled pool does not leak and then compare the technology with PVC liner pool technology.

The design and construction of tiled pools

Tiles can only be placed on walls and floors that are structurally rigid and that do not flex under water pressure, ground pressure or temperature change. If flexing occurs the tiles will come off. The tiles themselves are not water-proof and so the structure itself has to provide the water-proofing.

Across the globe such structures are often formed with Gunite that involves projecting concrete pneumatically at high speed onto a natural ground surface or onto a formed surface using shuttering. Reinforcement consisting of steel wires or rods is put in place before so that the gunite surrounds them and becomes "reinforced concrete". The method of construction allows both curved and flat shapes to be formed and is in common usage in Australia and the US. It does require good ground conditions because it is impractical to build thick sections using this technology.

In SW France the ground conditions are often poor at pool sites and so conventional reinforced concrete construction would be required. This involves the construction of a heavily reinforced  slab base (250 to 300 mm thick) and walls (180 to 200 mm thick).

In either case the structure must be designed by an experienced fully qualified civil / structural engineer who will take all the ground conditions, pool size, pool depth etc into account.

The most important construction issue relates to the joint between the heavy ground slab and the walls. The slab obviously has to be cast first. The shutters for the walls are then erected and the walls concrete poured a day or so later. This results in a joint that is virtually impossible to water-proof in a 200 mm thick wall.

Hence the water-proofing is provided by a water-proof membrane that is applied to the surface of the very expensive pool structure. The quality of the membrane and the leakiness of the pool relies entirely on the materials used, the mix proportions, the mixing and the skill and integrity of the plasterer.

Other pool construction issues

There are various other construction  issues that need to be taken into account in the design and installation of a ceramic tiled pool and these include:

1. The concrete base slab and the walls will need to be cleaned by water blasting, shot blasting, grit blasting etc to ensure that the render / screed sticks on - these are all very dirty processes that take a lot of time to undertake
2. The concrete base slab and the walls will need to be levelled with render / screed  to get the necessary flatness for tile installation (< 3mm in 3m) - this may also need cleaning before the membrane is applied
3. After levelling the waterproof membrane will need to be applied - this will be a proprietary latex based product mixed with Portland cement that will stop moisture penetration, moisture expansion, chemical attack by chlorides and efflorescence. The membrane will need to cure for 7 days at 20 + degrees C.
4. After curing the pool will need to be flood tested for leaks - this will involve filling at a slow rate of 600 mm in 24 hours. Fugitive dyes and a scuba diver will be required to locate any leaks
5. Mosaic tiles will need to be paper faced ceramics as back mounted mosaics can come off the wall following saturation and pool water chemical attack
6. Tiles must be impervious or vitreous to reduce the effects of moisture expansion and to eliminate freeze / thaw problems
7. The tile mortar bed must be latex based to reduce chemical attack and improve flexibility to withstand moisture expansion and shrinkage or epoxy based (expensive and can be difficult to use)
8. The grout can be latex based or epoxy based - epoxies can discolour under sunlight.
9. Movement joints must be provided in the tiling in strict accordance with the grout manufacturer's installation instructions
10. The latex based beds and grouts will need to cure for 14 days at 20 degees C (10 days for epoxies)
11. Pool to be filled at 600 mm per 24 hours to prevent excessive water pressure, thermal and moisture differentials. Filling should not proceed in direct hot sunlight or with very cold water

It is no wonder that these sorts of pools take so long to build and are so susceptible to leakage.

Pool Operational Issues

The control of pool water chemistry is very important in ceramic tiled pools:

1. Chlorine uses and depletes calcium and so calcium balance is essential to prevent deterioration of cement based grouts and mortars
2. If the pH is too high mineral deposits will form on the tiles and grout - they can form under the surface of the ceramic tiles causing the surface to come off the tiles
3. If the pH is too low acidic etching of the grouts and mortars can occur
4. If the calcium hardness is too low the pool water will etch calcium from the grout and if it is too high calcium deposits can form on any of the pool surfaces
5. At normal pH values iron and copper metals will come out of solution and can then be deposited as stain on tiles, grout and pool fittings

Another common problem is that the skimmers become loose in the concrete wall in which they are built. This results in leakage that can only be cured with putty that is unsightly and likely to be picked out by small fingers!

PVC liner pool technology

When everything is taken into consideration it is difficult to understand why anyone would want to take the risk of building a ceramic tiled pool - that is why we do not build them!

PVC liner pools:

• Will not leak even under quite large structural movements in the pool walls and floor
• Can be renewed comparatively cheaply (800 to 1000 euros) and easily on a DIY basis
• Allow leaks to be easily located and repaired (this will be the subject of a future weblog)
• Are virtually impervious to chemical attack (calcium deposition can occur but PVC is much easier to clean than tiling and grout)

And last but not least they look terrific!

In summary PVC liner pools cost half of what ceramic tiled pools cost and are superior in just about every way. They are based on the latest material technology and are environmentally friendly because of the reduced requirement for energy intensive cement and steel products. Ceramic tiled pools are based on 40 year old technology that relies on modern chemical additives to work!

Will Witt