The special properties expanded perlite adds as a concrete aggregate provide the same functional value for cement-based plasters as well. They include:
Lightweight. Cementitious perlite plasters weigh up to 60% less than common sand plaster.
Insulative. Gains of as much as 4X thermal transfer resistance over sand plasters. Noise transfer through walls is also reduced.
Fire Retardant. Up to a 4-hour fire protection rating is achievable at minimum weight and thickness; fire-tested designs by recognized laboratories are readily available.
Strong. Strength and cracking resistance are easily obtained using glass or polypropylene fibers. Various admixtures improve workability and stickiness.
Perlite Plaster
Expanded perlite particles are made up of millions of microscopic air bubbles suspended in a glassy foam matrix. Replacing part of all of the sand in a plaster mix design with perlite provides insulative (both thermal and sound transfer) properties at a significant weight savings. The mix design can the be further tweaked for strength and workability using various admixtures.
Perlite plasters and cements have been in use for over half a century and are well understood. They are highly adaptable, easy to handle, stable, and durable.
The Perlite Institute publishes a perlite plaster installation guide that covers prep, mixing and application. The guide also provides sample mix proportions and physical property numbers referenced to ASTM standards.
Textured Coatings and Finishes
Textured finishes on ceilings and walls rise, fall, and rise again in popularity, subject to the whimsical current of style. When interior design trends call for texture, perlite makes an excellent lightweight texturizing aggregate for sprayed-on or rolled-on finishes. Perlite is available in different grades, thus provided depth-of-texture options. Other advantages include an extremely lightweight form factor, providing low-cost bulk filling and savings in shipping and handling costs. The light weight of the perlite particles also reduces run and sag tendencies—allowing a heavier coating in a single pass. The bright whiteness of expanded Hess Perlite reduces color pigmentation costs. Inorganic and inert, the perlite does not contribute to yellowing.
Perlite also has application in sound insulation, both in sound-blocking and sound-absorbing products (including as a filler in spray-on absorbers).
