Swimming Pool Balance Tanks Lining, London

THE PROBLEM

The swimming pool in a new build development had been in service for a short period. During drain down for maintenance the balance tanks were inspected and several issues were observed. This included cracking in the concrete, water ingress and significant salt deposits.

During our site survey we identified that a cementitious tank lining had previously been poorly applied, without even filling the blow holes in the concrete. This had provided a route for highly corrosive chlorine to penetrate the concrete.

The tanks were located in a sub basement area, within a basement plant room. This presented access challenges that had to be considered as part of the tank lining solution.

THE SOLUTION

We identified the following key stages to this tank lining project;

  1. Resolving water ingress and preventing future water transmission which could pose a risk of osmotic blistering in any tank lining applied
  2. Protecting and preserving the concrete from degradation as a result of the ingress of chlorine
  3. Applying a suitable sealing tank lining

Initially the active leaks were resolved by method of resin injection to enable the refurbishment works to commence. This was undertaken using Normet Tampur 150 .

This hydrophilic polyurethane resin foams upon contact with water and forms a flexible seal to prevent ground water ingress.

Once active leaks had been resolved the next step of the tank relining process was to remove the existing poorly applied cementitious tank lining. This was undertaken by combination of vacuum controlled diamond grinding and vibration damped breakers. The previous tank lining had been applied to extremely inconsistent thicknesses – with the floor having been applied extremely thick.

The prepared concrete exposed significantly more blow holes – these must be filled before the application of tank linings as they cannot be filled with coatings alone.

To mitigate against both the damage that could have been caused by chlorine ingress into the concrete and the risk of osmotic blistering in the new tank lining, we proposed the application of Aquron 7000 & 2000 throughout the tanks.

Aquron 7000 is a powerful anti corrosion treatment for steel reinforcing in concrete and is based upon the same colloidal silicate technology as Aquron 2000. Aquron 2000 can penetrate up to 200mm in the concrete and forms a hydrogel that fills porosity in the concrete, thus reducing moisture transmission and mitigating against osmotic blistering in the new impermeable tank lining.

This is a significant risk when lining buried concrete structures, with the concrete serving as a semi permeable membrane.

To all of the tank corners where the worst water ingress had previously been witnessed Remmers Stopaq was applied and sealed using a cove detail. The purpose of this was to guard against any future movement in the tank allowing water ingress in these areas, which would cause the swellable sealant to expand and thus form a pressure tight seal.

At the floor wall interface which is always a point highly susceptible to movement a waterproofing bandage was applied, which is deliberately debonded to allow any movement to occur beneath. This bandage is also able to withstand up to 1 Bar of negative water pressure without allowing water ingress.

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To provide a blow hole free surface to apply the new tank lining to the walls were treated using a cementitious slurry coat – avoiding the mistake made by the previous tank lining contractor. This was allowed to cure and hydrate naturally.

Prior to application of tank lining materials the moisture content of the concrete was tested and recorded as part of our standard quality assurance. The climatic conditions with regard to temperature, relative humidity and dew point were also tested and recorded to ensure compliance with the manufacturers recommendations.

All surfaces were primed using Amchem P IV highly damp tolerant polyurethane primer to ensure optimum adhesion and sealing of the cementitious surfaces to prevent pin holing and outgassing in the new tank lining.

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Because of the evidence of cracking in the structure Amchem Drythane 400 HE was then applied to a nominal thickness of 500 microns. By combining this with a coat of Amchem Drythane standard at a nominal thickness of 500 microns this creates a tank lining which can crack bridge up to 10mm from a previously non existent crack.

Wet film thickness readings were taken throughout the tank lining application to ensure that the desired thicknesses were achieved.

Finally as part of our standard tank lining quality assurance all surfaces coated were tested for pin holing and porosity using a DC holiday spark tester. This is essential in chemically demanding environments such as swimming pool balance tanks as a single pin hole would allow chlorine to enter the concrete again, potentially allowing the corrosion of the steel reinforcing.