Sound control, whether achieved through an adhesive or an underlayment, is an essential component of a hard surface flooring installation. In commercial projects, sound control will help meet building code requirements. In residential homes, a noisy hardwood or resilient could result in an angry callback. FCI convened a panel of industry experts to discuss both adhesive and underlayment systems for sound control.

Our panelists include: Mike Micalizzi, Custom Building Products senior director, technical services; J. Alex Keene, Dependable division manager, floor preparation; David Jackson, DriTac field technical services manager; Arthur Mintie, Laticrete senior technical services director; Jeff Johnson, MAPEI business manager, floor covering installation systems; Beth Lee, Maxxon senior development and project manager; Deanna Summers, MP Global Products marketing coordinator; Brian Petit, NAC Products vice president of operations; John Serraino, QEP vice president of product management; Sean Gerolimatos, Schluter Systems technical director; Blair Roberts, Schönox HPS North America marketing coordinator; Wayne Williams, Stauf director of training and technical/sales support; Mark Lamanno, Titebond/Franklin International technical market manager, flooring; and Brett Fleury, USG product marketing manager, tile and flooring solutions.

What are the pros and cons of choosing adhesives versus underlayments for sound reduction?

Micalizzi: When used in tile and stone floor applications, sound reduction membranes meeting ANSI A118.13 provide multiple benefits to the occupants of a multi-story building. Primarily, there’s a reduction of impact noise from footfalls, especially high heels, and these membranes can also provide important crack isolation protection.

The reduction of impact sound is measured in decibels and stated as an impact insulation class (IIC) rating. The actual decibel reduction in an assembly when recorded in a laboratory setting is listed as the delta, or difference made by the membrane. The thickness of the membrane typically improves the performance.

Another valuable benefit from the use of these membranes is providing crack isolation from existing crack movement in concrete, future cracks and assisting with movement from substrate deflection. Membranes meeting ANSI A118.12 requirements accommodate movement from 1/16” to greater than 1/8”. Our membranes are rated as ‘High Performance’ and exceed 1/8”.

There are some limitations for certain types of sound reduction membranes in respect to point loading, tile types and tile sizes. To absorb sounds, they are designed to be less dense, so consult product technical datasheets to decide which is right for your project. Adhesives used for sound reduction membranes vary.

Lee: Sound-reducing adhesives are not a widely adopted solution for floor applications in multifamily environments where minimum sound code is required. There is a lack of sound test data for this type of product in the industry. Sound control mats installed directly under the finished flooring are very popular for carpet to LVT conversions in multifamily renovations.

In new wood frame construction, a sound mat plus gypsum underlayment installation is always recommended because it provides permanent sound control and improved sound reduction in low frequencies, which are commonly found in multifamily construction.

In multifamily renovations and concrete new construction, sound control mats installed directly below the flooring are generally easy to install and most will achieve minimum code. It is important that if code must be met, the flooring contractor request sound control tests specific to the project’s assembly. Many acoustical consultants recommend seeing both lab and field tests to prove the mat or adhesives actually perform when installed with normal field installation methods.

Fleury: Adhesives do not decouple the floor covering from the framing system; therefore, an adhesive can never achieve the kind of improvement in sound transmission you can get from a sound mat and gypsum underlayment.

In multifamily construction the floor/ceiling assembly is required to be fire rated. The underlayment is there to achieve the code-required fire rating as its primary purpose. The mass that an underlayment provides improve both the sound transmission class (STC) and impact insulation class (IIC) per Section 1207 of the International Building Code (IBC). An adhesive as a replacement for an underlayment will not help meet the building code for a fire rating.

Sound mats/boards used in conjunction with a gypsum-based underlayment provide an economical, permanent sound solution that addresses both airborne (STC) and structure-borne (IIC) sound transmissions for the life of the building. In new or old construction. Addressing sound after the fact is very difficult and, in most cases, can’t be addressed just from the top of the floor/ceiling assembly. Topical solutions, although effective in some cases, may have to be replaced every time a new floor covering is installed.

Mintie: When choosing the specification and selection of an appropriate sound reduction product, one should begin with the targeted Impact Insulation Class (IIC) rating required for the specific project. From there, a comparison of the available sound reduction product performance properties can be made to select the ideal product.

The pros and cons of choosing an adhesive versus an underlayment mat for sound reduction go hand in hand. For some, adhesives are the preferred method for sound control because they take the place of costly, time-consuming underlayment mat systems by allowing for faster, more effective tile or stone installations.

“When choosing the specification and selection of an appropriate sound reduction product, one should begin with the targeted Impact Insulation Class (IIC) rating required for the specific project. From there, a comparison of the available sound reduction product performance properties can be made to select the ideal product.”

– Arthur Mintie

However, adhesives are not ideal for all types of floorcoverings. This is where underlayment mats come in. Underlayment mats for sound control often include a wide array of mat thicknesses and ultimate IIC values, making them possible to be used in all types of flooring projects rather than limited to tile or stone. 

Johnson: The advantage of selecting an adhesive that provides sound control is that you can simplify the installation method down to a single step. The disadvantage of a single-step adhesive solution is that it is limited to a single application of adhesive, which is driven by the requisite coverage required by the flooring type.

For example, sound-controlling adhesives for wood flooring (solid or engineered) typically have a coverage rate of 30 sq. ft. per gallon. That means on average you are counting on all your sound control attributes to come from a layer of adhesive that is close to 1/16” thick. To double this thickness means you would be installing floor covering on a sea of adhesive, which would be extremely difficult and messy.

The same situation would be applicable to installations of LVT and LVP. Here you need to work with pressure-sensitive types of adhesives and those thicknesses of application are considerably thinner than those of wood flooring types. There is no way really to increase their thicknesses and their sound control abilities without huge cost increases and a lot of mess.

Sound control underlayments can be tailored to any thickness and to virtually any sound control requirement based on their applied thickness. Sound control mats range in thickness from 2 mils to 1/2” or greater.  Composition will also range from polyurethane foams, cork, reground rubber, cork/rubber composites and the list goes on. True, they require multiple steps and increase overall build height of the floor, but they also offer customizable solutions for sound control greater than what you can get with from a single-step dual-function adhesive solution. 

Jackson: Each of our adhesive technologies holds an appealing value for different reasons to different people. The same concept is true with our sound control product selection. We offer both system adhesives and underlayment and allow the installer to decide which they prefer to work with. When utilized together, DriTac adhesives and underlayments form a Total Sound Reduction System (SRS) with a lifetime warranty from a trusted single-source supplier.

Pros for using system adhesives center around a one-step application process. Pros for using underlayment are rooted in a tried-and-true method that has been used successfully for many years. Some of the top foam and rubber underlayments in the market carry the most optimal sound control ratings available.

Underlayments also offer installers a valuable flexibility through the potential employment of different product thicknesses. Finished floor height disparities can be minimized by different thicknesses of underlayment. Underlayment can also help overcome minor subfloor irregularities.

Gerolimatos: There are several pros to using adhesives or underlayments for sound reduction, the first being that underlayments often provide multiple functions. For example, sound-reduction underlayments may offer uncoupling or crack isolation capabilities. Another advantage is that they can be used in combination with other sound control measures, such as sound-rated ceilings.

A con to using underlayments for sound reduction is they can increase total floor thickness. The mass of an underlayment is one of the greatest contributors to the sound reduction performance, and increasing the thickness is a common way to increase the mass of an underlayment. Another disadvantage is many underlayments designed for sound reduction are compressible and may provide poor load support to the floor covering, which can lead to reduced service life of the assembly.

Williams: Using a sound-reducing adhesive saves time since you don’t have a two-step process of gluing the underlayment and then the hardwood. The cost of two layers of adhesive usually is more expensive than just using the one layer of sound-reducing adhesive. Additionally, labor costs are saved because you don’t have to pay the installer to spread two layers of adhesive or cut in the underlayment.

However, some sound-reducing adhesives are more expensive than using two layers of regular wood adhesive.

Petit: It is important to understand the characteristics of the sound material being used and ensure that it meets at least the minimum sound requirements. Rigid products like tile or marble should be installed over a product that won’t compress (understand the point load), which could crack the flooring.

Lamanno: One major advantage of using adhesives versus underlayments is that the underlayment will result in a hollow sound; it doesn’t sound like a solid floor. When the substrate is flat and you can create a continuous film from the adhesive, you can achieve a more solid feel. However, adhesive doesn’t work as well as a sound barrier on uneven substrates because the adhesive in low spots does not create a continuous film. There will be gaps that allow sound transmissions to lower levels and moisture that can affect the flooring above the film. The unevenness of the subfloor will create hollow spots.

Serraino: While some adhesives do have higher sound ratings than underlayments, you can find products of either type to fit your needs depending on the job at hand. Using adhesives means higher costs—both in product and installation—with additional skill requirements. There may also be some restrictions based on jobsite conditions. Additionally, moisture barriers may be needed. 

Keene: The biggest advantage of choosing a sound-reducing adhesive over an underlayment is time savings. Eliminating the underlayment reduces a step in the installation process. However, not all flooring products require an adhesive for installation.

Furthermore, relying on an adhesive alone can limit the potential for sound reduction. It should be noted the use of an adhesive does not always preclude, or eliminate, the need for using an underlayment. The Dependable StepSoft product, for example, could enhance the performance of an acoustical adhesive. 

Are there situations when one of these product types should be chosen over the other?

Fleury: In renovations of existing multi-family wood-framed buildings, topical sound attenuation systems may be the only solution. Removing the existing floor covering and underlayment, installing a sound mat and then re-pouring the floor would certainly be more cost-prohibitive. Over concrete slabs or planks, you may be limited by an overall height restriction which may prevent you from installing a sound mat (1/8” to 3/4”) with 1/2” to 1 1/4” of underlayment. This is when a thin topical acoustical system becomes more palatable from an economic standpoint.

Serraino: This will depend on the desired installation type. In the instances when a floating floor is desired, the use of underlayment is acceptable and you may use a moisture barrier, etc. In other instances, when the floor needs to be adhered and sound suppression is a part of the requirement, then the obvious choice is adhesives with sound suppression.

Both installation methods are used often and sometimes required in the design of a building. Also, in some cases the installation will require a cork underlayment to be glued down to the substrate, then the floor glued down to the underlayment. This process can get expensive with additional labor and adhesive costs. Sound suppression of the glue can thus become a cost-saver.

Mintie: When there are several competing products with similar sound ratings, a contractor should always compare each product’s Delta IIC results to determine the sound performance the tested product will actually provide to the substrate.

Typically, adhesives are best suited for ceramic and porcelain tile finishes as well as natural stone. They are also ideal for renovation projects where finish heights have already been established due to their thinner system profile build up.

Underlayment sheet mats work best under other types of glue-down finishes, such as hardwood, making them more versatile when various finishes require sound control.

Johnson: The main decision drivers for the choice of sound control solutions are available money, sound reduction requirements, limitations on build height and flooring type. There is no situation where one sound control solution is typically better than another as it is all really dependent on building code requirements and which system fits that requirement within the expense budget allowed.

“ The main decision drivers for the choice of sound control solutions are available money, sound reduction requirements, limitations on build height and flooring type. ”

– Jeff Johnson

Lamanno: If a floating floor is desired, an underlayment would be the correct choice. The pad can either be floated or adhered using adhesive. If you choose to adhere the pad, you would ‘double stick’ it, applying adhesive to the subfloor and then on top of the pad to adhere the flooring. A floating pad works well when a particular type of flooring (such as old vinyl asbestos or perimeter-bonded vinyl floors) is going to be covered and is difficult or problematic to remove. The double stick method also eliminates the hollow sounds that a non-adhered pad creates.

Gerolimatos: In most circumstances, sound reduction performance is only a portion of the expected capabilities of a floor assembly. Other functions must also be considered.  For example, a bathroom floor would benefit from uncoupling and waterproofing. Each job can be different and should be evaluated for its particular needs or challenges. 

Jackson: The ultimate choice for attaining the best sound control properties possible for any given project is to utilize adhesive and underlayment together. This system approach provides a solid-sounding floor free of hollow-sounding areas and optimizes sound abatement to the highest degree. Whether underlayment is utilized or not, gluing a floor down helps achieve optimal results for consumers.

Flooring adhesives should only be utilized when the flooring manufacturer recommends that the product can be glued down. When a particular flooring product is not recommended for glue-down installations, underlayment is the best option to implement sound control properties within the flooring system.

Williams: Situations where using both an underlayment and adhesive may be a better option would be if the added height of the system is needed to meet up to another flooring product. Using just the adhesive would work better in the reverse situation—when adding to the height would cause an issue of meeting the other flooring.

Petit: The type of substrate and the finished flooring to be installed can help determine which products to use. However, it is important that the products are mold- and mildew-resistant, meet at least the minimum ratings for impact insulation class (IIC) and sound transmission class (STC), and meet the ANSI specifications for setting the finished flooring. 

Summers: Consumers with chemical sensitivities often choose nailed-down floors to avoid the need for adhesives. Underlayments that don’t need to be glued down are an excellent option for these consumers.