Acoustical Plaster in Construction

Acoustical Plaster

Sound absorption just got even better.

If you're looking for a material that is monolithic, has no breaks, seams, or joints, and can be finished in any color; your only options are drywall or plaster. Unfortunately neither of these products abosrb sound. And when you're looking at a large room with hard floors and gypsum walls, sound absorption can be critically necessary. The solution to this is acoustical plaster.

What is Acoustical Plaster?

Acoustical plaster is used in a wide variety of commercial and residential applications. It is completely monolithic and can be finished in almost any color.  Some are manufactured with an aggregate, while the best systems typically contain fibers (cotton) which have some inherent advantages. Acoustical plaster is typically applied in thicknesses ranging from 3mm (1/16") to 40mm (1.5").

Cotton based acoustical plaster systems are easy to install and refinish at anytime. They can match any custom color, and even be made to look like stone, marble, or cement. The most common application is a silk finish, which is troweled and installed to look perfectly smooth.

Acoustical plaster is completely fireproof, and LEED rated. It can withstand some basic environmental turbulence, so long as the humidity does not exceed 70%, and the system does not come in direct contact with liquids. The plaster is porous to sound, and other molecules can pass through with direct contact.

Most Common Applications

Acoustical plaster is used in areas that need high sound absorptive qualities. In New York City (NYC), New England, Connecticut, and Long Island, the most frequent applications include:

  • Museums
  • Auditoriums
  • Libraries
  • Galleries
  • Performing arts centers
  • Mid/high-end retail locations
  • Transportation hubs
  • High-end residential homes
  • Education facilities
  • Office lobbies and conference rooms

Until now, architects have primarily sought out and specified a silk finish. Advancements in plaster manufacturing techniques have led to the ability to product custom finishes, such as stone, marble, and cement as shown above. As of 2017, the only manufacturer that can create these finishes is Fellert. See our comparison guide for details.

The  Fellert Silk finish  applied in brilliant white.

The Fellert Silk finish applied in brilliant white.

Acoustics and Sound Information

Acoustical plaster can dramatically decrease the sound reverberation in a given area. Reverberation has an important impact on speech intelligibility, affecting safety, health, learning, and quality of life. By absorbing sound waves, acoustical plaster makes conversation clearer, even in harsh situations, by reducing reverberation time. 

In areas with high volumes of people, especially where the walls and floor may be made of hard surfaces, sound absorption can be vital to the overall room aesthetic. 

Most acoustical plasters have an noise reduction coefficient (NRC) of 0.50 - 1.00. This can vary significantly depending on the mounting style (Type A or Type E), the finish, and the manufacturer. For specific acoustic information about each style and manufacturer, please see our Acoustical Plaster Comparison article.

Mounting Styles

Acoustical plaster can be mounted in two ways. The final application choice should be selected by the architect based on the projects specifications and requirements.

Direct to substrate (Type A)

With Type A mounting, gypsum board is first installed to a level 1 finish. All HVAC, electrical, fire sprinkler and other penetrations are sealed with traditional drywall tape or a self-adhesive fire-tape to prevent air movement between the occupied space and the plenum. 

Alternative substrates are: concrete, existing plaster, GFRG surfaces, and previously painted GWB. These substrates would need to be tested for bond strength, cleaned and sanded smooth. The acoustical board is attached to the substrates with the adhesive and if required, secured spring washers.

Suspended - Direct to Framing (Type E)

With Type E mounting, the acoustical board and plaster are installed directly to the drywall grid. The substrate is constructed without a layer of GWB. The acoustical boards are mechanically attached to drywall grid thereby eliminating the need and cost for a layer of GWB. There is an increase in sound absorption performance in the low frequency range with the direct-to grid installation method which is commonly referred to as the E-400 or E-200 mount and/or air gap behind.

Plaster Only (3mm thickness)

As an alternative to the the other systems that require an acoustical board placed behind the finish system, the acoustical finish can be sprayed on directly to the substrate for a small increase in acoustical performance. 

Alcro Tät Primer is applied to a drywall substrate prepared to a level 4 standard. The primed surface is then sprayed with the Even Better Acoustical plaster. Alternative substrates such as concrete, existing plaster and previously painted GWB would need to be prepped accordingly and ensure they are sound and free from cracking.

To learn more about acoustical plaster or specify it on your next project, reach out. From conceptual design to product selection, specification, and installation, Design Strategies has been helping architects and contractors since 1995.