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Thames Water Tank Base Coating, London

THE PROBLEM

The originally applied protective coating/screed to the tank base has largely failed. Anecdotally this was thought to be as a result of lack of surface preparation prior to tank lining application.

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THE SOLUTION

As requested we provided a quotation for the removal of the existing failed tank lining and the application of suitable replacement tank lining to the concrete tank base.

Due to uncertainty over whether a damp proof membrane was installed beneath the slab, we proposed the application of Sikagard M790. As well as offering excellent resistance to waste water and offering crack bridging, this material is also vapor permeable. This made it ideal for this application where uncertainty over the presence of a DPM meant that osmotic blistering could be a risk, and by using this tank lining system would help to mitigate this risk.

Initially the failed tank lining was removed by method of high pressure water jetting (10,000 psi) and preparing the concrete simultaneously.

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Once all arisings had been removed it was apparent that whilst the concrete surface was very well prepared, a significant profile had been created.

We therefore took the decision to conduct secondary preparation in the form of vacuum controlled diamond grinding in order to lessen the peaks of the surface profile.

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All surface to be coated were then vacuumed clean in order to ensure the best possible adhesion of the new tank lining, which would be disrupted if a layer of dust was present on the surface.

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As part of our standard quality assurance when applying tank linings to concrete the moisture content of the concrete was tested and recorded.

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This is not strictly required for this tank lining system as it has no substrate moisture content limitations.

To ensure the correct relative humidity and dew point as per the manufacturers recommendations indirect oil fired heating and dehumidification was introduced. Again as part of our standard tank lining quality assurance the climatic conditions were tested and recorded prior to tank lining application commencing.

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All prepared surface were then primed using Sikagard P770 applied by method of brush and roller at a practical coverage rate of 0.4Kg/m2.

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Once cured the first coat of Sikagard M790 was applied in a red colour at a practical coverage rate of 0.6Kg/m2.

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Throughout the tank lining application wet film thickness readings were taken suing thickness combs to ensure the correct tank lining thickness was achieved.

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The second coat of Sikagard M790 was then applied in the same manner and consumption rate in the contrasting grey colour.

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By using contrasting colour for each layer of the tank lining system this aids applicators in achieving full and uniform coverage and is considered best tank lining practice.

The cured tank lining was tested for pin holing by method of spark testing. A single pin hole is a point of tank lining failure, making this a critical quality assurance step.

Finally the sealant at the floor/wall interface which had been removed as part of the preparation works was reinstated using Sika  TS Plus applied using sealant guns and bladed flush.

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The works from start to finish were completed in two weeks and once complete enabled the client to return the tank to full operational service.