Waste tank and septic tank lining is the system that prevents effluent from escaping into the environment and the groundwater. The challenge here is not water pressure but chemical attack. Acids and gases generated in an effluent environment gradually destroy ordinary concrete and ordinary coatings.
Why special materials are required
As organic matter breaks down in effluent, hydrogen sulphide is released. On damp surfaces above the liquid this gas converts to sulphuric acid and attacks the concrete. This is known as biogenic sulphuric acid corrosion and its effect is greatest in the zone above the water line.
For this reason ordinary cementitious coatings are inadequate in waste tanks. Epoxy or polyurea coatings with certified chemical resistance are used.
Choosing the system
Epoxy coatings
Provide high chemical resistance and good adhesion. They are rigid, so they should be used with care where structural movement is expected. Surface moisture is critical during application.
Polyurea coatings
Spray applied, very fast curing and capable of high build in a single pass. They are elastic with high crack bridging capacity and shorten programme time in large structures.
Chemically resistant cementitious systems
Usable in less aggressive environments and as a preparatory layer. On their own they do not withstand a high acid load.
What governs the application
Surface preparation. Half the job. Degraded concrete is removed down to sound substrate and the profile made good with repair mortar where needed. A coating applied to a weak surface lifts within a short time.
Moisture and ventilation. Solvent vapour and effluent gas accumulate in an enclosed space. Forced ventilation and gas monitoring are needed both for worker safety and for coating quality.
Thickness control. In a chemical environment thickness directly determines service life. The material used must be divided by the area and verified.
Details. Pipe entries, hatch frames, floor to wall junctions and cold joints are resolved with separate products.
Safety
Septic and waste tanks are confined spaces. There is a risk of oxygen deficiency and toxic gas. Gas monitoring before entry, continuous ventilation, a safety harness and an attendant stationed outside are mandatory. No one should enter the tank without these measures in place.
Frequently asked
Can an existing septic tank be refurbished
Yes. Once the tank is emptied, cleaned and the surface prepared, the coating can be applied. Where there is serious loss of concrete section, structural repair comes first.
How long does it take
Emptying, cleaning, drying and cure times determine the overall programme. With polyurea systems curing is rapid, so the tank returns to service sooner.
Does it solve odour problems
Once the tank is sealed, odour escaping from it is greatly reduced. The correct operation of the vent stack should also be checked.
The condition of your tank, its chemical load and access conditions are assessed on site to determine the right coating system and programme.