Our client owned two anaerobic digester sites, both of which had tanks which had been lined using an incorrect tank lining specification. Following our tank lining being applied on their first site we were engaged a year later to reline their digester tank on the second site.
The existing tank lining was a sprayed rubber emulsion, meaning that it could not be removed by grit blasting as the abrasive would bounce back, resulting in a very slow removal rate.
Fortunately we have at our disposal our own Ultra High Pressure Water jetting unit which is ideal for removing elastomeric tank linings such as this.
Following the removal of the existing tank lining the concrete was prepared by method of grit blasting to remove any remaining tank lining from within the profile of the concrete and to raise a surface profile where required.
A termination rebate was cut into the concrete to provide a suitable finishing point for the new polyurea tank lining.
To ensure excellent adhesion and fully seal the surface to prevent pin holing in the new polyurea tank lining all surfaces to be coated were double primed using a damp tolerant epoxy primer, applied by method of airless spray.
When polyurea tank linings are applied they create an exothermic reaction which can reach temperatures in excess of 90 degrees centigrade. This reaction can force any moisture or trapped air to the surface, creating pin holes in the lining. By applying two coats of primer this is minimised.
All joints were sealed using a polyurethane jointing compound prior to the application of Corrolastic UB to a thickness of 2mm. This polyurea tank lining material has excellent resistance to hydrogen sulphide and biogenic sulphuric acid which is found within anaerobic digesters.
As part of our standard tank lining quality assurance the new polyurea lining was spark tested to check for pin holes. Where found these were rectified using the same polyurea material.
Finally the previously cut termination chase was sealed using a polyurethane jointing compound.
We warranted this tank lining for 10 years from completion, with the polyurea lining having an expected service life in excess of 25 years.