Stonbury were recently commissioned to carry out refurbishment works to the gas zone of a Digester. The inspection to the soffit, revealed that the existing coating had failed and that the exposed concrete had suffered from attack by the Hydrogen Sulphide gases.
It was decided that the existing failed coating system should be removed from the soffit, extending 1m down the walls. Utra high water jetting was the preferred preparation method, however after an initial attempt that left traces of well adhered coatings, reparation was completed by open grit blasting.
This method also left a key to the substrate, ideal for the application of a new protective coating system. Following grit blasting a termination chase was formed 1m down the wall, ready for the new system to be addressed into.
After removal of spent grit, the digestor was jet washed clean. Any repairs identified to the soffit, deeper than 5mm were repaired with rapid set high density repair mortars. This was followed by the application of a cementitious levelling compound to all prepared areas, to provide a suitable surface for the subsequent coatings.
After 5 days cure on the levelling compound, a primer and 2 full coats of a chemically resistant, elastomeric, polyurethane coating was applied by brush and roller, terminated into the previously formed chase, and sealed using a single pack polyurethane joint sealant. Materials were then left to cure and the digester was handed back.