THE PROBLEM
The primary settlement tank was leaking sewerage into the surrounding environment as a result of cracking in the concrete walls caused by subsidence in the surrounding soil. A temporary repair had been enacted but a more permanent solution was required.
SOLUTION
Given the history of movement and potential for future movement a highly flexible tank lining solution was required. We proposed the appreciation of SPI Corrolastic HT – an extremely flexible yet also high tensile polyurea tank lining.
Whilst it is not possible to guarantee that if significant subsidence or movement occurs in the future that it will not exceed the limits of the tank lining, this tank lining material gives the greatest chance of longevity.
Following the overpumping of the primary settlement tank to reduce the water level the area to be treated was first cleaned by method of high pressure washing. Excess water was removed using wet lift vacuums and all surfaces to be coated were prepared by method of vacuum controlled diamond grinding.
Cracks with the concrete were expressed using a vacuum controlled diamond saw and repaired using a high strength epoxy mortar. Where the wall had fallen away from the slab the void was gravity fed with epoxy resin prior to the installation of a resin rich epoxy mortart fillet to isolate this potential point of moment from the new lining and increase the elastic movement potential of the polyurea tank lining.
All surfaces to be coated were double primed using an extremely damp tolerant epoxy primer, with the first coat incorporating an accelerator to allow two coats to be applied in the same shift. An aggregate dressing was broadcast into the second coat of primer to provide an excellent mechanical bond for the polyurea tank lining to adhere to.
To ensure compliance with the manufacturers recommendations and as part of our standard quality assurance moisture content of the substrate and climatic conditions were monitored and recorded.
A termination chase was cut at the perimeter of the repair using a vacuum controlled floor saw as per best polyurea application practice.
Areas not to be coated were masked, utilising a specific tape for the application of polyurea materials that incorporates a cutting wire to overcome the fast curing nature of the tank lining material – it turns from liquid to a solid in less than 10 seconds.
The fast curing nature of polyurea materials allows additional thickness to be easily applied for additional strength over cracks and weak points.
SPI Corrolastic HT was applied to thickness of 2mm, with additional thickness applied over cracks in the structure. SPI Corrolastic HT can elongate close to 400% providing an extremely flexible tank lining.
Polyurea tank lining was checked for porosity using a DC holiday spark tester and repairs made where necessary using the same material.
A particular benefit of SPI Corrolastic HT is that it contains their patented Ultrabond molecule which allows the material to bond to materials beyond their conventional overcoating window. This is particularly applicable to polyurea tank lining materials which can have an overcoating /re coating window as short as 4 hours, dependent on ambient temperature. Conventionally these areas would need to be solvent wiped before making good.
The fast curing nature of the polyurea tank lining meant that the repaired tank could be returned to service the same day. In total these works took two days from start to finish, minimising over pumping durations and costs.
