Original Article Journal of Fire Sciences 1–19 Ó The Author(s) 2017 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav DOI: 10.1177/0734904117709479 journals.sagepub.com/home/jfs Size is not all that matters: Residue thickness and protection performance of intumescent coatings made from different binders Michael Morys, Bernhard Illerhaus, Heinz Sturm and Bernhard Schartel Date received: 21 September 2016; accepted: 21 April 2017 Abstract In addition to the acid source, charring agent, and blowing agent, the binder is a crucial part of an intu- mescent coating. Its primary task is to bind all compounds, but it also acts as a carbon source and influences the foaming process. A series of intumescent coatings based on five different binders was investigated in terms of insulation, foaming, mechanical impact resistance, and residue morphology. The Standard Time-Temperature modified Muffle Furnace (STT MuFu + ) was used for the bench-scale fire resistance tests and provided data on temperature and residue thickness as well as well-defined residues. The residue morphology was analyzed by nondestructive m-computed tomography and scanning electron microscopy. A moderate influence of the binder on insulation performance was detected in the set of coatings investigated, whereas the foaming dynamics and thickness achieved were affected strongly. In addition, the inner structure of the residues showed a rich variety. High expansion alone did not guarantee good insulation. Furthermore, attention was paid to the relation between the microstructure transition induced by carbon loss due to thermo-oxidation of the char and the development of the thermal conductivity and thickness of the coatings during the fire test. Keywords Intumescence, morphology analysis, computed tomography, fire resistance, bench-scale fire test, fire protective coating Bundesanstalt fu ¨r Materialforschung und -pru ¨fung (BAM), Berlin, Germany Corresponding author: Bernhard Schartel, Bundesanstalt fu ¨r Materialforschung und -pru ¨fung (BAM), Unter den Eichen 87, 12205 Berlin, Germany. Email: bernhard.schartel@bam.de