The effluent pit was allowing ground water ingress which meant that the effluent tank which the pit feeds was having to be emptied more frequently. The pits intended purpose is to catch leaks of fuels and oils from surface drains, which meant that it was a significant concern that these could mix with ground water.
Any tank lining solution applied would have to be able to resist fuels and oils.
When lining below ground concrete structures where there is evidence of ground water ingress there are two important considerations;
Combing these two considerations with the chemical resistance required we proposed the application of Raven Lining 405. This ultra high build epoxy tank lining not only offers the chemical resistance required for exposure to fuels and oils, but is also specifically designed for application to below ground structures.
Upon entering the tank it became apparent that the main point of water ingress was where a plastic pipe penetrated the concrete. This is a common problem as cementitious materials contrary to common belief do not bond well to plastic.
Initially the area around the plastic pipe was injected using Normet Tampur 150 hydrophillic polyurethane resin. This reacts with water upon contact and forms a flexible fluid tight seal, preventing water ingress.
As a belt and braces approach a rebate was broken out around the pipe and filled using Remmers Stopaq – a permanently elastic swellable sealant which reacts with water to again form a pressure tight seal that does not rely on adhesion to difficult substrates such as HDPE. This was contained within a mortar fillet to ensure that the envisaged expansion was in the correct directions in order to achieve maximum fluid tightness.
Once the active water ingress into the pit had been resolved we were able to commence preparation for the tank lining itself. All surfaces to be coated were prepared by method of vacuum controlled diamond grinding, followed by vacuum cleaning to prevent dust disrupting the bond of the new tank lining. This is especially critical when there is potential for a negative load to be applied to the rear face of the tank lining.
If we had been applying a conventional tank lining at this point it would have been necessary to apply a cementitious fairing coat to fill blow holes and irregularities in the concrete surface that cannot be filled with conventional coatings.
However in this application because of the ultra high build properties of Raven Lining 405 which allow the tank lining to be applied in this case at 6mm thick in a single application, this was not required as the material itself will fill blow holes.
Raven Lining 405 was applied using notched trowels to gauge that the correct thickness had been applied and then finished using a steel float. Although not required for this application the material is extremely damp tolerant, making it ideal for buried concrete pits and tanks.
Once cured the tank lining was checked for pin holing using a DC holiday spark tester to ensure that the tank was both liquid tight for the fuels and oils contained, but also performing the waterproofing required for this application.
