This paper will discuss the types of hand applied and spray applied sound absorbing acoustical plasters manufactured by Pyrok Inc. Pyrok Acoustement products are spray applied acoustical plasters which are formulated with gypsum plaster or Portland cement. The Portland cement Acoustement 40 can be used for exterior as well as interior applications. Acoustment Plaster 20 and Acoustment Plaster 40 are gypsum based and are for interior applications only. The Pyrok StarSilent System has a smooth hand trowel applied finish that looks like monolithic drywall as well as a superfine sprayed finish. This paper will also discuss ASTM C423 testing and how it relates to spray and hand applied acoustical plasters. Although all spray applied and hand applied sound absorbing products are tested to ASTM C423, there are differences and inconsistancies when evaluating and comparing their sound absorption data.