2025
London
BACKGROUND
A concrete tank base used for wastewater storage had suffered significant failure of the previously applied protective coating and screed system. It was believed that this deterioration was due to inadequate surface preparation prior to the original lining application. The client required a long-term, durable solution to reinstate full operational capacity of the tank.
OUR SOLUTION
Corroless Eastern Limited were appointed to carry out the removal of the existing failed tank lining and install a robust Sika tank lining system. Given the uncertainty regarding the presence of a damp-proof membrane beneath the slab—and the associated risk of osmotic blistering—the decision was made to specify Sikagard® M790, a crack-bridging, highly chemical-resistant, and vapour-permeable tank lining system. Its permeability made it particularly suitable for applications where moisture entrapment beneath the slab is a potential concern.
SURFACE PREPARATION
The initial step involved the removal of the existing coating system using 10,000 psi high-pressure water jetting, which simultaneously prepared the concrete substrate. Once cleared, the surface exhibited a pronounced profile. To reduce excessive peaks and optimise conditions for the new lining, vacuum-controlled diamond grinding was subsequently performed.
All prepared surfaces were then vacuum-cleaned to remove any residual dust, ensuring optimal adhesion of the new tank lining system.
MOISTURE & CLIMATIC CONTROLS
Although Sikagard® M 790 does not require specific substrate moisture content limitations, standard QA procedures were followed, including concrete moisture testing. Indirect oil-fired heating and dehumidification were used to control relative humidity and dew point, with all climatic conditions recorded prior to the application.
APPLICATION PROCESS
Step 1: Primer Application
All prepared concrete surfaces were primed using Sikagard® P770, applied by brush and roller at a practical coverage rate of approximately 0.4 kg/m². This priming layer ensured optimal adhesion for the subsequent coating system.
Step 2: Tank Lining Installation
Once the primer had cured, two coats of Sikagard® M790 were applied. The first coat, coloured red, was applied at 0.6 kg/m², followed by a second coat in grey at the same coverage rate. Using contrasting colours helped applicators achieve full and uniform coverage while also assisting with quality assurance checks. Throughout the process, wet film thickness was regularly measured using comb gauges to ensure consistency.
Step 3: Final QA and Sealing
Following full cure of the tank lining system, spark testing was carried out to identify any pinholes, as even a single defect could compromise the protective integrity. Finally, the sealant at the floor-to-wall junction was reinstated using Sikaflex-403 Tank & Silo, applied and tooled flush to complete the system.
THE OUTCOME
The works were completed within a two-week programme. Following successful QA testing and inspection, the tank was returned to full operational service. The use of the Sikagard® M790 system provided the client with a high-performance, long-lasting solution that offers excellent resistance to wastewater environments while mitigating the risks of moisture entrapment.
PROJECT PARTICIPANTS
Products Used: Sikagard® M 790, Sikagard® P 770
Contractor: Corroless Eastern