THE PROBLEM
The primary settlement tank was leaking from the top 1 metre of the brick walls, with extensive cracking visible in the structure.
Polyurea Settlement Tank Lining, Norfolk
THE SOLUTION
Due to the extensive cracking in the structure we proposed the application of a highly elastic polyurea tank lining in the form of Specialty Products Incorporated Corrolastic HT.
Initially all surfaces to be coated were prepared by method of vacuum controlled diamond grinding to ensure a clean and profiled surface to ensure excellent adhesion of the polyurea tank lining.
Any cracks in the structure were expressed using a vacuum controlled diamond saw and repaired using a high strength concrete repair mortar. Anchor rebates were cut at the top and bottom of the areas to be coated with polyurea to provide an anchored termination for the polyurea lining an prevent the creation of an exposed edge which would be prone to allowing liquid ingress and could lead to the undermining of the polyurea lining.
Once prepared as part of our standard quality assurance the moisture content of substrates to be coated was checked using a Tramex moisture meter. Climatic conditions were tested and recorded each shift prior to any tank lining application taking place.
All surfaces were double primed using a damp tolerant epoxy primer. When applying polyurea coatings and tank linings we always apply two coats of primer (double prime). The reason for this is that once the polyurea material is mixed within the spray gun the material exotherms up to 100 degrees centigrade. The effect this has on the substrate is that any entrapped air within the substrate is heated and expands, causing pin holing in the polyurea tank lining. This is obviously highly undesirable when you trying to create a seamless polyurea tank lining and by applying two coats of primer helps to ensure the substrate is fully sealed.
Because of the external nature of this application the second coat of primer as fully blinded using a pigmented quartz aggregate to ensure that even if inclement weather was experienced between the application of the primer and the polyurea tank lining excellent mechanical adhesion of the polyurea membrane would still be achieved.
Something also to be considered when applying epoxy materials externally is the risk of amine blush /blooming. This occurs when the still curing material is exposed to moisture, causing the amine curing agent to form a waxy layer at the surface and a milky appearance. This layer prevents proper adhesion of subsequent layers, something that can again be mitigated by fully broadcasting the surface with an aggregate dressing.
A filet detail was installed at the wall/horizontal interface to isolate this point of potential movement and create an elongation multiplier in this area.
After extensive masking to ensure a neat finish SPI Corrolastic HT was spray applied to a polyurea membrane thickness of 2mm, with additional thickness being applied in known areas of cracking and areas prone to movement.
This is one of the key benefits of polyurea tank linings in that the very fast gel time (8 seconds approximately) means that additional thickness can easily and quickly be applied in these areas.
The other key benefit is the high elongation properties and high tensile nature of the material, with elongation of over 300%. This means that any future movement should be accommodated with splitting the lining and compromising fluid tightness.
As part of our standard quality assurance the polyurea lining was checked for porosity using a DC holiday spark tester and any defects identified marked and made good using the same polyurea tank lining material.
Finally the previously cut termination chases were sealed using a polyurethane jointing compound to ensure a seamless and fluid tight finish.