The remote potable storage reservoir tank was in an extremely poor condition, heavily leaking water and with the external protective coatings exhibiting significant deterioration.
We were requested to quote for a Regulation 31 approved tank lining system and a suitable and long lasting external protective coating.
For the tank externals we proposed the application of Rustoleum Noxyde Plus as a suitable protective coating. We proposed this for the following reasons;
Initially all surfaces were treated with a biocidal wash given the tanks extensive coverage of organic growth.
This was followed by the preparation of all external surfaces by method of 10,000 psi water jetting, exceeding the manufacturers preparation requirements, removing all loose and unsound coatings.
Once prepared (despite being highly unlikely to be present given the preparation method) soluble salt tests were conducted to ensure that these were not present above specified levels. If left in place soluble salts lead to osmotic blistering by drawing moisture through the coating film.
Similarly surfaces to be coated were checked for cleanliness by means of dust tape test as per ISO 8502-3 to ensure that all surfaces were sufficiently clean in order to ensure optimum adhesion of the new protective coatings.
Before and during each coating application shift climatic monitoring was undertaken to ensure compliance with the manufactures recommendations again as part of our standard quality assurance
Following application dry film thickness readings were taken to ensure that a minimum thickness of 350 microns had been achieved.
The tank internals contained a loose fitted thermoplastic liner, which given the leakage observed had obviously perforated or split.
The tank internals were then thoroughly cleaned by method of high pressure washing to remove dirt and organic matter that had accumulated under the failed tank lining.
This is a common problem with this type of tank liner, where leaks can go undetected with water stagnating unseen.
Prior to abrasive blasting again chloride tests were undertaken to ensure that these soluble salts were not present on the tanks internal surfaces. It is essential that if present these are removed prior to abrasive blasting as failure to do so will lead to them being forced further into the surface profile during preparation works.
Given the tanks aluminium construction we reduced the blasting pressure and selected a finer abrasive and lightly abrasive blasted the tank walls to prevent introducing too much heat into the panels, which could potentially distort and warp the aluminium.
The surface profile was tested and recorded using a surface profile needle gauge in order to ensure compliance with Instructions for Use (IFU) and ensure maximum adhesion of the new tank lining.
The concrete floor was prepared by method of vacuum controlled diamond grinding in order to lessen surface irregularities.
All surfaces were then vacuumed clean and dust tape test assessments again conducted.
Because of the tanks construction, the surrounding ground conditions and it being impossible to verify the waterproofing arrangement on the soil side of the tank base it was decided not to apply the coating to the concrete base.
The reason for this is that when impermeable coatings are applied to concrete where moisture is present, this can lead to phenomenon called osmotic blistering, where the concrete and/or the primer act as a semi permeable membrane as shown in the diagram.
To mitigate this risk the concrete was instead treated by the application of Aquron 2000 – a Regulation 31 approved colloidal silicate waterproofing treatment that can penetrate up to 200mm into the concrete. This forms a hydrogel that fills pores in concrete, serving to waterproof and protect the steel reinforcement.
To protect the prepared tank walls from overspray these were sheeted prior to the application of Aquron 2000 by method of airless spray.
This was allowed to penetrate for 72 hours over a weekend as per the manufacturers recommendations prior to the application of further coatings.
Heating and dehumidification were then introduced to ensure the correct climatic conditions for application of Acothane DW as per the IFU
Where we were overlapping the Acothane DW tank lining from the walls on to the concrete the moisture of the concrete was tested and no coatings applied until it was sufficiently dry as per the IFU.
The concrete overlap was then primed using Acothane LV sealer applied by brush and roller. Being lower viscosity this primer penetrates the concrete to gain better adhesion and also seal porosity that could lead to pin holing in the main tank lining.
This is something that is often overlooked during tank lining application, which can be detrimental to quality and finish. If tank lining materials are too cold they will be too viscous, resulting in over application and likely sags and runs.
As per the IFU and best tank lining practice a stripe coat was applied to all angles, edges, nuts, bolts and welds. This ensures full film build / tank lining thickness were coatings pull thin through surface tension and gravity.
Wet film thickness readings were taken during application and dry film thicknesses post application.
All previously marked areas were then touched in by brush.
Finally at the floor/wall interface and to cracks in the floor a flexible debonded bandage was applied where movement was most liable to potentially occur.
This can elongate up to 400% and is deliberately only adhered at the perimeters. This allows the central section to freely expand and contract if movement does occur.
