Frequently Asked Questions

Acoustical plaster is a wall or ceiling finish system that absorbs sound energy while presenting the appearance of a smooth, continuous plastered surface. It is designed to be invisible as an acoustic treatment: from across a room, an acoustical plaster ceiling is visually indistinguishable from conventional plaster. The acoustic function is contained within the material itself.

BASWA acoustical plaster systems achieve this through two coordinated mechanisms. At mid and high frequencies, sound energy passes through a micro-porous marble aggregate finish surface and is dissipated as heat within a mineral fiber or natural fiber panel beneath. At low frequencies, the surface of the system acts as a diaphragm, vibrating in response to bass energy and converting those vibrations to heat as well. This dual-mechanism absorption allows BASWA Phon to achieve Noise Reduction Coefficient (NRC) ratings up to 1.00 across the full audible frequency spectrum, as independently tested per ASTM C423.

The result is a surface that manages room acoustics without any visual evidence of doing so, which is why acoustical plaster is used in everything from concert halls and broadcast studios to private residences and boardrooms where the quality of the acoustic environment matters but the introduction of visible acoustic treatment is not desired.

Learn more about Acoustical Plaster and how it is used in a variety of project types >

Download third-party test data for BASWA systems >

Sound absorption and soundproofing are two distinct acoustic strategies that address fundamentally different problems, an important distinction when specifying acoustic materials.

Sound absorption reduces the acoustic energy reverberating within a room. Absorptive materials convert reflected sound into heat rather than allowing it to bounce from surface to surface. The practical result is a reduction in reverberation, echo, and ambient noise levels inside that space. Acoustical plaster is a sound-absorbing material.

Soundproofing, or sound isolation, addresses the transmission of sound between rooms through a wall, floor, or ceiling assembly. It is measured by ratings such as Sound Transmission Class (STC) for airborne noise and Impact Insulation Class (IIC) for impact noise like footsteps. These are properties of an entire assembly, not a single finish material.

BASWA systems are specified for sound absorption. They can also contribute 5 to 7 STC points to a rated wall or ceiling assembly when installed as part of a comprehensive acoustic strategy, but that contribution is secondary to their primary function. If the design goal is to prevent sound from traveling between rooms, a dedicated isolation assembly is the appropriate solution.

Additionally, a system like BASWA DTG provides a Ceiling Attenuation Class (CAC) Rating of 39. This is important in scenarios where the wall between rooms does not extend to the floor deck, and sound traveling through ceiling assembly and over the wall into the next room is a concern

Learn more about Sound Absorption versus Soundproofing >

Reverberation time, expressed as RT60, is the time in seconds that it takes for a sound to decay by 60 decibels after its source has stopped. It is one of the most consequential metrics in architectural acoustics because it directly determines speech intelligibility, listening comfort, and the subjective acoustic character of a space.

Rooms with long reverberation times produce overlapping sound reflections that obscure speech and music, create a sense of noise that grows louder as more people speak or move, and generate a listening fatigue that occupants experience as stress. Hard-surfaced lobbies, gymnasiums, open-plan offices, and dining rooms are common examples where unmanaged reverberation creates a measurably poor acoustic environment. Research in peer-reviewed acoustics literature consistently links excessive reverberation to reduced speech intelligibility and negative effects on concentration and wellbeing.

The appropriate target RT60 varies by room type and use. A recording studio, a classroom, a restaurant, and a concert hall each require different reverberation conditions calibrated to their function. Acoustical plaster reduces reverberation time by converting reflected sound energy into heat, allowing designers and acousticians to bring any space within its performance target.

Learn more about Acoustical Consultants and how to locate an engineering firm >

The foundational test for any absorptive acoustic material is ASTM C423, the Standard Test Method for Sound Absorption and Sound Absorption Coefficients by the Reverberation Room Method. Always request third-party test data measured in accordance with ASTM C423. Results should report absorption coefficients at individual octave-band frequencies (125 Hz through 4000 Hz at minimum) as well as the single-number summary ratings: the Noise Reduction Coefficient (NRC) and the Sound Absorption Average (SAA).

Mounting method matters significantly. BASWA systems are tested using both A-mounting (surface-mounted) and E-mounting (suspended) configurations to accurately represent the range of real-world installation conditions. A product tested only under ideal mounting conditions may perform differently in a typical application. Request data that reflects your anticipated installation.

Other ratings you may encounter: Ceiling Attenuation Class (CAC) measures a ceiling system's ability to blocksound through a shared plenum between adjacent rooms. Sound Transmission Class (STC) measures an assembly's resistance to airborne sound transfer between rooms. Impact Insulation Class (IIC) measures resistance to impact noise and is not applicable to wall or ceiling finish products.

NRC and SAA are the primary performance indicators for sound absorption. All other ratings describe different acoustic properties and should not be substituted for absorption data when evaluating a material's performance within a room.

Understanding NRC ratings >

Understanding SAA ratings >

Understanding CAC ratings >

Understanding STC ratings >

Download third-part test data for BASWA systems >

Standard drywall and plaster are acoustically reflective surfaces. When sound strikes them, energy bounces back into the room, increasing reverberation and ambient noise levels. Acoustical plaster is engineered to absorb that energy rather than reflect it. BASWA systems deliver up to ten times the sound absorption of standard drywall, as demonstrated by independently tested data per ASTM C423.

Suspended acoustic ceiling tiles and foam or fabric-wrapped acoustic panels accomplish sound absorption as well, but through a fundamentally different physical and aesthetic approach. They are visually identifiable as acoustic treatments, are generally limited to flat horizontal applications, and introduce a grid or panel geometry that definesthe ceiling plane. Acoustical plaster creates a continuous, monolithic surfacethat can be applied to flat, curved, domed, vaulted, and compound-curved ceilings and walls. It is visually identical to traditional plaster and imposes no constraint on ceiling form.

A newer category of product includes spray-applied cellulose and gypsum-composite panel systems marketed under commercial brand names as seamless acoustic finishes. These differ from BASWA systems in several important ways: they are typically tested as isolated materials rather than as complete engineered systems, they may use binders or compounds that bridge acoustic porosity, and they vary in durability, impact resistance, and finish quality. BASWA systems are independently tested as complete installed assemblies per ASTM C423, are formaldehyde-free and VOC-free, and use non-water-soluble marble aggregate finishes specifically developed for longevity. The distinction matters most at the specification stage, when the performance data being compared should reflect equivalent testing conditions.

How acoustical plaster compares to acoustic ceiling tiles and panel systems >

BASWA acoustic offers sixsystems, each engineered for specific performance requirements, substrate conditions, environmental demands, or project priorities.

A brief orientation to each:

BASWA Phon‍
The flagship system and the most widely specified. BASWA Phon consists of a mineral wool supporting panel adhered to a stable substrate and finished with a micro-porous marble aggregate finish. Available in 30 mm, 40 mm, and 70 mm panel thicknesses, it achieves NRC ratings from 0.80 to 1.00 depending on thickness and finish. Suitable for flat, curved, domed, vaulted, and compound-curved ceilings and walls.

BASWA NaturalA hemp and flax fiber based seamless acoustical plaster system applied directly to ceilings and walls. BASWA Natural achieves 51% less CO2 per square meter than mineral wool systems, making it the specification of choice for projects with rigorous embodied carbon targets. It captures sound energy through the same micro-porous marble aggregate finish used across the BASWA line, with absorption into a randomly-spun natural fiber layer. Compatible with domes, groin vaults, complex curves, flat ceilings, and walls. Available in 30 mm and 40 mm thicknesses, it achieves NRC ratings from 0.60 to 0.85 depending on thickness and finish.

BASWA Basic
‍An acoustical plaster system engineered for greater impact resistance and expedited installation timelines on flat ceilings and walls with a stable substrate. BASWA Basic is well suited to high-humidity environments and projects with tight construction schedules, with finish options that allow the complete system to be installed in as few as 1 to 2 days. Available in 30 mm thickness, it achieves NRC ratings from 0.70 to 0.75 depending on finish.

BASWA DTG
‍A direct-to-grid acoustical system that delivers the seamless aesthetic, durability, and sound absorption of a BASWA finish on a suspended ceiling grid. DTG is often specified for commercial acoustic ceilings where construction speed is a priority but a monolithic marble finish is still desired. It allows designers and contractors to align acoustic, visual, and scheduling goals without sacrificing finish quality. Available in 30 mm thickness, it achieves NRC ratings from 0.75 to 0.80 depending on finish.

BASWA Cool
‍BASWA Cool integrates hydronic cooling or heating behind the acoustic finish, combining sound absorption with draftless, noise-free radiant temperature control in a single continuous surface. It delivers the acoustic performance of BASWA Phon while supporting mechanical comfort goals without visible diffusers, grilles, or registers. Particularly relevant in high-performance buildings that prioritize energy efficiency and occupant wellbeing. Available in 30 mm, 40 mm, and 70 mm thicknesses.

BASWA Hybrid
‍A niche add-on panel used in specific high-performance applications. BASWA Hybrid serves two primary roles: as a backing panel for extending a BASWA finish onto surfaces beyond the primary acoustic system, and as an impact-resistance wall panel for spaces where surface durability is needed. It is also used in performance spaces requiring targeted high-frequency absorption. Third-party test data for BASWA Hybrid is available upon request. Available in 10 mm thickness, it achieves NRC ratings up to 0.30 depending on finish.

System selection should be guided by the acoustic consultant's or architect's target reverberation time calculations, the substrate and ceiling geometry, the project's environmental and sustainability goals, and any schedule constraints. The BASWA technical team is available to assist with system selection at any stage of the design process.

BASWA Systems Comparison and Overview >

BASWA systems are installed across a broad range of project types, from highly technical performance venues to residential interiors where acoustic comfort is a design priority. Past installations include concert halls, university auditoriums, broadcast and recording studios, sports arenas, museums, natatoriums, airports, corporate headquarters, religious institutions, restaurants, and private residences.

The common denominator across these project types is not building category but design intention: an acoustically refined interior surface that performs without visible acoustic treatment. For some projects, that means achieving a specific reverberation time required by a performance program. For others, it means improving speech intelligibility in a conference room or reducing noise fatigue in an open-plan office. For residential clients, it often means addressing echo and reverb in a high-ceiling living space, home theater, or listening room without sacrificing the aesthetic of the architecture.

BASWA systems are equally applicable to new construction and renovation. In historical renovation projects, BASWA Phon can be applied directly over an existing stable plaster substrate, preserving original architectural detail while introducing modern acoustic performance.

Browse the BASWA project portfolio >

Learn more about acoustical plaster in:
Historical Renovation | Restaurants | Residences | Museums | Offices | Schools | Courtrooms

Yes. BASWA systems are engineered for high-humidity environments. BASWA systems are availabel for a variety of conditions, with BASWA Basic being suitable in conditions up to 90% relative humidity and 30°C (± 2°C ). BASWA's technical team is available to help guide you through the selection process to find the system most suitable to your project,

BASWA finishes are not water-soluble, and each system achieves a score of 10 out of 10 for mold resistance per ASTMD3273. Past installations in humidity-demanding environments include natatoriums, spas, gyms, yoga studios, porte-cocheres, and covered outdoor spaces.

In spaces where the surface may be subject to direct, incidental water contact, application of BASWA Protect is recommended to maintain a hydrophobic barrier.

Download the High Humidity data sheet >

Yes. BASWA systems are very compatible with leading sustainability and occupant health certification frameworks. Health Product Declarations (HPDs) are available for all BASWA products and Environmental Product Declarations (EPDs) are available for BASWA Phon and BASWA Natural systems.

BASWA systems acheive a ≤ 0.5 mg/m3 VOC content per California Section 01350 and have no Living Building Challenge Red List materials. Each system contains 43 to 83% recycled content per complete system. The light reflectance L-value of 89.6 to 91.3 per ASTM E1477-98 contributes to daylighting strategies relevant to LEED and WELL credits.

BASWA Natural offers 51 percentless embodied CO2 per square meter than mineral wool systems, making it particularly relevant for projects pursuing aggressive carbon reduction targets or Living Building Challenge certification.

BASWA acoustic's manufacturing process uses natural and recycled raw materials and heat-recovery-optimized production.

Review LEED v5 contributions and download the BASWA Sustainability data sheet >

The cost of BASWA acoustical plaster systems varies based on project size, system, finish, location, and installation complexity. BASWA acoustic provides budget information on request and works directly with certfied contractors to provide material quotes that are then used to develop project specific installed pricing with labor.

Contact BASWA for budget-level guidance early in the design process  to support project feasibility and specification  decisions.

Request a quote or budget >

BASWA finishes are made with recycled marble aggregate and are applied either by hand trowel or by spray to deliver monolithic acoustics. The primary distinction between finishes is the aggregate grain size, which determines the texture and degree of surface smoothness achievable.

Classic Fine and Fine use the finest aggregate option (0.5 mm grain size) while Classic Base, Base, and Frost use a slightly coarser aggregate (0.7 mm grain size). Two-coat finishes are recommended for applications with critical, grazing lighting conditions. One-coat finishes offer labor and time savings and are suited for surfaces without grazing light conditions.

When design calls for texture or custom designs, BASWA finishes can be hand-troweled or spray-applied to replicate specific material aesthetics, including polished concrete, stone, stucco, and old-world plaster. Custom hand-painted motifs are also achievable on a BASWA surface using water-based paints.

Standard and Custom Texture finish options >

Yes. BASWA systems offer virtually unlimited color customization through the BASWA Color tint additive, which is integrally mixed into the finish coat material prior to application for uniformity. Custom colors can be produced to coordinate with any design palette, and multi-color gradient designs are achievable.

Because color is built into the material rather than painted on after installation, it does not affect the acoustic porosity of the surface and has no impact on acoustic performance.

If a decorative mural or accent painting is desired on an existing BASWA surface, a water-based paint that does not bridge microscopic pores must be used and applied carefully. Conventional paints seal the surface porosity that makes the system acoustically absorptive. Any refinishing of a BASWA surface with standard paint will result in a measurable loss of acoustic performance and is not recommended. For color changes on an existing installation, contact BASWA acoustic to discuss approved refinishing options.

Custom color and finish options >‍

Yes. BASWA Phon, BASWA Cool, and BASWA Natural are engineered for non-planar surfaces and can be applied to flat ceilings, flat walls, curved walls, domed ceilings, groin vaults, barrel vaults, and compound-curved surfaces of any configuration. BASWA Basic is designed for flat ceilings or walls. BASWA DTG is designed for flat or slightly curved ceilings.

Panels are installed down to a 2-foot radius curve. For complex surfaces, panels are factory-kerfed on the back face to increase flexibility and conform to the required geometry. Mechanical fasteners used during the adhesive curing period are removed after the adhesive sets, and the resulting holes are filled with BASWA Fill, ensuring a seamless finished surface with no telegraphing of fasteners over time.

Browse the BASWA project portfolio for inspiration >

Yes. All BASWA systems are designed to integrate with standard ceiling components including recessed lighting, HVAC diffusers, fire sprinkler heads, concealed speakers, and access panels. These elements are roughed in at finished ceiling height before panel installation, and all cut-outs are made on-site to ensure precise fitting.

Concealed speakers can be recessed directly into the BASWA panel, meshed, and finished with the same acoustic coat to create a fully integrated, acoustically transparent, visually invisible speaker installation. Trimless access panels up to 8 feet by 8 feet are available.

Review the Installation process >

See how fixtures are incorporated >‍

Access the library of details per systems >

Yes. BASWA finishes that are trowel-applied smoothly function as high-quality projection surfaces, based on the finish's light reflectance L-value of 91.3 per ASTM E1477-98. The combination of acoustic absorption and projection capability in a single surface eliminates the need for a separate screen in environments where projection must work in tandem with acoustical design.

Notable projection installations include planetariums, museum galleries, and the New World Symphony Hall in Miami.

See project case study for New World Symphony Hall project >

BASWA acoustic provides full specification support to architects and engineers throughout the design and construction document phases. Available resources include Master Spec-format project specifications, product and system data sheets, shop drawing coordination, and sustainability requirment support.

The BASWA technical team works directly with design professionals from early-stage system selection through construction. The recommended approach is to engage BASWA early in schematic design so that the correct system, thickness, and finish can be integrated into the project plan before structural and mechanical decisions are fixed.

Download technical data and guide specifications >

Guide on specifying BASWA acoustical plaster systems >

Yes. BASWA acoustic works directly with every member of a project team, including architects, interior designers, acoustical engineers, general contractors, and owners. BASWA provides technical support, specification assistance, and certification documentation to any team member who needs it.

BASWA can provide acoustical engineers will find detailed octave-band absorption data and dual-mounting ASTM C423 test results available for use in reverberation calculations. Architects and designers can request finish samples, specification documents, and technical drawing details. Contractors can gain contacts to their local certified installer network.

Learn more about Acoustical Consultants and how to locate an engineering firm >

Contact BASWA acoustic for technical guidance > ‍

All technical documentation for BASWA systems is available on our Downloads page. This includes acoustic test data, sustainability documentation, guide specifications, details, guides, and applicable certification references. For specific submittal information or project documentation not available for download, contact BASWA acoustic directly.

Contact BASWA acoustic for technical guidance >

BASWA Phon, Basic, Natural, and Cool system panels are adhered to stable, sealed sustrate using a plaster-based adhesive. For these systems, acceptable substrates include standard drywall with taped joints (Level 1 tape only; no finish coat is required on tape or fastener heads), concrete, intact existing plaster, and GFRG forms.

All penetrations not already sealed with drywall tape must be sealed with adhesive tape prior to panelinstallation. A fully sealed substrate prevents air infiltration through the installed system, which is the primary cause of discoloration over time in products that do not achieve a fully airtight assembly. BASWA systems can also be applied directly over existing stable plaster in renovation applications, preserving original architectural details.

BASWA DTG panels are installed on a drywall framing grid and do not require a continuous substrate.

Substrate preparation and panel installation >

BASWA systems are typically installed at the same point in the construction schedule as lay-in ceilingtiles. The following conditions must be met before installation begins:

• Substrate is installed and taped to Level 1
• All substrate penetrations are sealed with drywall mud,tape, or adhesive-backed tape
• Drywall abutting the application area is primed
• Required scaffolding is fully assembled and electrical power is available on-site
• The installation area is conditioned to appropriate temperature and humidity ranges

Engaging BASWA early in the project schedule is strongly recommended. System selection, substrate specification, and rough-in coordination for lighting and mechanical components all benefit from early involvement.

Contact BASWA acoustic for early project coordination >

A typical BASWA Phon, DTG, or Natural installation takes 4 to 5 days from panel installation through final finish coat. Typical drying time between coats is overnight. BASWA Basic's expedited installation options allow the complete system to be installed in as few as 1 to 2 days.

Every project differs in scope and complexity. Contact BASWA acoustic to discuss scheduling for a specific project.

BASWA systems are available globally through a network of certified independent installers. Installers are trained and certified directly by BASWA acoustic to ensure consistent system performance and finish quality across all project types. Certification involves on-site training and ongoing technical support through a contractor-dedicated program.

New companies may pursue certification through BASWA acoustic's technical sales department. To find a certified installer for a specific region or project, contact BASWA acoustic directly.

Contact BASWA acoustic to find a certified installer >

Learn more about becoming a certified installers >

BASWA systems are not designed with a finite service life. The marble aggregate finish is highly durable, non-water-soluble, and resistant to the normal conditions of an interior environment. Because the acoustic function resides in the porosity of the material rather than in a surface coating that can degrade or peel, the acoustic performance of a properly maintained BASWA installation does not diminish with age.

BASWA acoustic supports the long-term performance of installed systems through a dedicated maintenance product line: BASWA Protect applies a protective layer that repels water and dirt before they become embedded in the surface; BASWA Clean is formulated for surface cleaning without closing acoustic pores; and BASWA Fresh allows for surface refinishing when needed. These products are designed specifically to extend the life of an installation without compromising its acoustic performance.

BASWA maintenance product line and guides >

When simple dust and finger print removal using common tools are not sufficient, BASWA acoustic offers a full line of Cleaning and Maintenance solutions.

BASWA Clean is surface cleaning product for BASWA systems and finishes. BASWA Protect is applied proactively to repel water and dirt before they become embedded in the surface. BASWA Fresh is used for surface refinishing when BASWA Clean is insufficient. These products refresh the surface without closing its pores.

For significant staining, BASWA acoustic's technical team can evaluate the condition and recommend the appropriate approach, which may include surface cleaning, localized or full surface refinishing, or application of BASWA Protect to prevent recurrence.

BASWA maintenance product line and guides >

Contact BASWA acoustic for maintenance guidance >

Yes. BASWA systems can be repaired using techniques similar to drywall repair. BASWA acoustic's technical team and certified installers are trained in repair procedures.

Repair and patching guide >

Color change options are available for existing BASWA installations. The specific approach depends on the condition of the current installation and the desired result. Because conventional paint must not be applied to an acoustic surface, color changes require the use of BASWA-approved refinishing materials and methods. Contact BASWA acoustic to discuss refinishing options.

Warranties are available for BASWA system installations. Coverage terms are project-specific. Contact BASWA acoustic to discuss warranty terms for your project.