We were contacted by our client following the removal of the roof from the anaerobic digester. This had revealed some cracking and minor spalling in the top edge of the site cast concrete anaerobic digester.
During our site survey we also identified that the existing tank lining had broken down in areas, resulting in degradation of the concrete through exposure to Hydrogen Sulphide.
As the works had to be completed in October when we knew that achieving the correct climatic conditions for conventional coatings we proposed the application of an extremely damp tolerant tank lining system in the form of Sikagard P770 primer and M790.
This crack bridging and highly chemical resistant polyurethane tank lining has no dew point or relative humidity restrictions, only that the surface must be free from water and condensation.
Initially all surfaces were prepared by method of vacuum controlled diamond grinding in order to remove the existing failed tank linings and fully exposed any defects in the concrete. This provided a clean surface for the new tank lining to adhere to.
Cracks in the concrete were expressed using diamond saws and made good using a high strength epoxy repair mortar.
As part of our standard tank lining quality assurance the moisture content of the concrete and the climatic conditions were tested and recorded. This validated our decision to use the proposed tank lining system as whilst the surfaces were dry, the moisture content was over 5% and the surface temperature was not 3 degrees above dew point.
All surfaces to be coated were then primed using Sikagard P770. This was mixed with fine quartz where required to fill imperfections in the concrete.
