An investigation of primer adhesion and topcoat compatibility on the waterborne intumescent coating to structural steel

•Critical selection of primer and topcoat for WB intumescent coating.•Adhesion of primer on steel plate and subsequent intumescent coating and compatibility of topcoat with intumescent coating to be considered for an effective multi-coat system.•On various primers & topcoats, epoxy primer and acrylic topcoat is found to be suitable. The adhesion and compatibility between various layers within an intumescent coating system coated on steel plate is studied under ambient condition and at elevated temperature as per cellulosic fire heating regime. An intumescent coating system, which typically comprises of a primer layer, an intumescent coating layer and a topcoat, must strongly adhere to the steel structure during service period for an effective protection and foamed char should also be tightly intact on the structure. The adhesion of different anti-corrosive primers such as epoxy coating, alkyd coating and zinc silicate coating with steel plate and the subsequent intumescent coating along with various topcoats viz. polyurethane coating, alkyd coating and acrylic coating are evaluated by X-cut tape test and pull-off test methods. The microstructure of interface between the steel plate and the coating system layers is characterized by field emission scanning electron microscope. The compatibility of coating system and thermal properties of coatings were measured by thermal insulation performance and thermogravimetric analysis respectively. The role played by type of primer and topcoat for an intumescent coating on the performance of coating system has been established.