Zonolite Acoustical Plaster (USG period) / Hi-Lite Acoustical Plaster / Audicote

Zonolite Acoustical Plaster / Hi-Lite Acoustical Plaster / Audicote

Manufacturer: United States Gypsum Company (USG) Years Produced: approximately 1945–1970 Categories: Acoustical Ceiling Treatment, Spray Fireproofing Asbestos Type: Chrysotile

Product Description

Zonolite Acoustical Plaster, along with its closely related trade variants Hi-Lite Acoustical Plaster and Audicote, were spray-applied ceiling and wall treatment products manufactured by United States Gypsum Company (USG) during the postwar construction boom. These products were marketed and sold extensively from approximately 1945 through 1970, a period during which fireproofing and acoustic control in commercial, industrial, and institutional buildings were top construction priorities.

The products served a dual purpose. First, when applied to structural steel, concrete decking, and other building substrates, they provided fire-resistance ratings required under building codes for high-occupancy structures such as office buildings, hospitals, schools, and industrial facilities. Second, the lightweight, porous texture of the applied material helped dampen sound transmission between floors and within large open spaces, a desirable feature in schools, auditoriums, and commercial interiors of the era.

USG marketed these acoustical plasters under multiple brand identities, with Zonolite Acoustical Plaster being the most widely recognized. The Zonolite name also appeared on other USG vermiculite-based products of the period. Hi-Lite Acoustical Plaster and Audicote represented formulation and marketing variants sold to similar end-user markets during overlapping production years.

These materials were applied primarily through spray equipment by specialized applicator crews. Because they were sold in bulk bags of dry powder and mixed on-site before spraying, they were handled extensively at job sites throughout the construction industry.

Asbestos Content

Litigation records document that Zonolite Acoustical Plaster, Hi-Lite Acoustical Plaster, and Audicote contained chrysotile asbestos as a component of their dry-mix formulations. Chrysotile, the most commercially prevalent form of asbestos throughout the twentieth century, was incorporated into acoustical plaster products during this era to improve the material’s fire-resistance performance, enhance fiber bonding, and improve adhesion to overhead surfaces during spray application.

Plaintiffs alleged that USG incorporated chrysotile asbestos into these products at concentrations sufficient to pose an inhalation hazard to workers involved in mixing, spraying, finishing, and later-stage disturbance of the hardened material. Product identification in litigation has been supported through archived product formulation records, building specification sheets, purchasing records, and the testimony of former workers and supervisors familiar with the materials used on specific project sites.

Because these products were sold and applied over a roughly 25-year period, the precise asbestos content and formulation may have varied across production runs and product lines. Litigation records document that testing of bulk samples collected from structures where these products were applied has confirmed the presence of chrysotile asbestos in the hardened plaster layer.

Under the AHERA (Asbestos Hazard Emergency Response Act) framework, spray-applied surfacing materials of this type are classified as a category of asbestos-containing material (ACM) requiring specific inspection, management, and abatement protocols in schools and other regulated buildings.

How Workers Were Exposed

The nature of spray-applied acoustical plaster created multiple routes and phases of occupational asbestos exposure for workers involved throughout the product’s lifecycle.

Mixing and loading operations represented one of the highest-exposure phases. Dry bags of acoustical plaster powder were opened and poured into mixing equipment on the job site, generating clouds of fine airborne dust. Any chrysotile fibers present in the formulation became suspended in the air during this process. Litigation records document that workers performing bag handling and mixing tasks frequently worked without respiratory protection during these operations.

Spray application was itself a significant exposure event. Applicators and their helpers operated spray equipment that directed a high-velocity stream of plaster slurry onto overhead surfaces, including structural steel beams, metal decking, and concrete. Overspray, misting, and rebound material settled throughout the work area, exposing not only the spray crew but also other trades working nearby.

Finishing and texture work performed after initial spray application involved sanding, troweling, or brushing the partially set material, activities that litigation records document generated respirable dust. Workers in close proximity to these finishing operations faced continued fiber inhalation risk.

Disturbance by subsequent trades was another documented exposure pathway. Electricians, plumbers, HVAC mechanics, and other building tradespeople working in spaces where Zonolite Acoustical Plaster, Hi-Lite, or Audicote had been applied were exposed when drilling, cutting, or otherwise penetrating the plaster ceiling layer. These secondary exposures could occur years or decades after initial installation.

Demolition and renovation work in buildings constructed between 1945 and 1970 continues to present exposure risk. Workers involved in abatement, renovation, or demolition of structures where these products were applied may disturb intact or deteriorating asbestos-containing plaster.

Plaintiffs alleged that USG knew or should have known of the health hazards associated with chrysotile asbestos exposure during substantial portions of the production period, and that the company failed to adequately warn workers or the general public of these risks.

This article is provided for informational and legal reference purposes. It does not constitute legal or medical advice. Individuals with potential asbestos exposure claims should consult a qualified asbestos litigation attorney.