Study of gypsum plasters exposed to fire.

Experimental r es ul ts are r eported from a stud y in which small gypsum plaster specimens were exposed t o controlled fir es similar to those to which large building elements have been subjected in tests by a recognized standard method. The small sp ecimens were tested without eit her struc t ura l load or restraint. Their fire performances were judged on time to a temperature rise criterion. The r esul ts were analyzed to determine the effec ts on fir e performance of vari ation of mix ratio, aggregate type and de nsity, duration of aging, and relative humidity of the ambien t in which the specimens were aged. Mix ratio a nd aggregate density, over t he ranges normally u sed , had li t tle effect, if a ny, on fir e performance. The times to te mperat ure rise for perlite an d verm iculi te aggregate plas ters " 'ere essentially equal, but shorter t imes were obse rved for sanded plast ers. Duration of agin g and relative humidity of t h e ambient had a significant effec t on ly for short aging period s and very h igh relative humidity co ndi tions.