Maxx Minutes Blog

Cellulose Fiberboard – how does it REALLY measure up against Maxxon's Gyp-Crete®?

Cost has long been a deciding factor for decision makers in the construction industry.  Many gypsum underlayment system alternatives, including fiberboard systems, boast a lower price point, but how do they really measure up? 

Maxxon’s Gyp-Crete® is one of the most efficient fire and sound control products available.  The poured underlayment fills the space where the wallboard meets the floor, completely sealing room perimeters, protecting the base plates from the spread of fire and helping prevent smoke leaks.  The Maxxon underlayment dries, creating permanent sound control and added fire resistance.

Cellulose-based fiber board, commonly referred by the brand name Homasote®, is a sheet of compressed recycled paper bonded under high temperature and adhesives.  Its uses vary from arts and crafts to sound deadening underlayment in commercial and residential construction.  It claims to be a cost effective equivalent of a Maxxon Sound Control System, when in reality, a Gyp-Crete and Acousti-Mat® system have many superior features.

Cost and Labor
  • The average cost for a ¾" deep Gyp-Crete underlayment installation is around a dollar per square foot. Gyp-Crete is batch mixed onsite with sand and water and pumped into place by trained professionals who can install up to 20,000 ft2 per day. Maxxon gypsum underlayments can be walked on in as little as 90 minutes after installation, allowing other light subtrades to resume quickly.
  • Fiberboard installation requires mechanical fastening (glue and screw), which is extremely time and labor intensive. The average cost for fiberboard installation is roughly $1.35 per square foot and installs at a quarter of the rate that Gyp-Crete does; 4,000-5,000 ft2 per day.

    Floor Covering Considerations
  • Maxxon underlayments dry with a smooth flat surface ready to receive virtually any floor good.
  • Carpet and pad can be installed directly on fiberboard, while hard surface floor goods require an additional plywood or mortar underlayment installation. Homasote in particular, does allow for direct installation of LVT greater than 4 mm, however many resilient flooring manufacturers require a minimum psi of 3000, forcing the underlayment installer to install the additional underlayment layer before floor goods installation.

  • Maxxon underlayments, and the optional IIC upgrade of an Acousti-Mat sound control mat encased in the Gyp-Crete, become part of the building structure and last the lifetime of the floor, not just the floor goods.
  • Replacing floor goods will eventually damage fiberboard, requiring it to be replaced almost as often as the floor goods.

    Sound Ratings
  • Multifamily projects across the country require a sound code minimum of 50 IIC/STC. While both Homasote fiberboard and Gyp-Crete underlayment will help achieve code requirements, Gyp-Crete STC ratings will typically land on the higher end of the code spectrum. By upgrading to the Acousti-Mat system of an entangled mesh mat encased in Gyp-Crete, your project is protected from impact sounds as well. Without a sound mat you can expect to achieve code if your project is exceptionally built without cut corners or accidental flanking paths. Why take that chance? A well-designed sound control system will always include a sound control mat.
  • STC RATINGS:Transmission of airborne sound is largely controlled by the mass of the floor system. This effect is commonly estimated using the Transmission Loss Mass Law, which predicts an increase in STC rating by five points when the system mass is doubled. At a typical density of 115 pounds per cubic foot (pcf), a Gyp-Crete underlayment contributes more than four times the mass of a fiberboard layer (26-28 pcf), significantly improving sound performance.
  • IIC RATINGS: By upgrading to a Maxxon Acousti-Mat Sound Control System (entangled mesh Acousti-Mat encapsulated in Gyp-Crete), not only do you create permanent sound control, you also effectively reduce low frequency noise common to multifamily environments. Based on Maxxon sound data, and our extensive experience with entangled mesh mats, an air gap created by an entangled mesh mat is the most effective way of reducing low frequency noises, like barefoot walking, objects dropping, and chairs rolling. The air gap provides dead space to capture and disperse low frequency vibrations. Acousti-Mats create an air gap; Homasote® and other flat sound control mats do not.


    Additional Sound Considerations
  • Maxxon underlayments are pumped into place, allowing them to flow over floor height variances and create a smooth, flat surface ready for flooring installation. As the underlayment dries, it stiffens the floor, virtually eliminating bouncy, squeaky floors.
  • Fiberboard is fastened to the subfloor, making it impossible to address floor height variances. Settling of a building structure may upset nails and screws in the fiberboard, leading to bouncy, squeaky floors when walked on. By mechanically fastening direct to the subfloor, not only do you lose the air gap, but now introduce flanking paths, furthering the opportunity for sounds to transfer through the floor.

    Fire Ratings
  • Maxxon sound control and underlayment systems are listed in over 100 UL Fire Ratings. Maxxon gypsum underlayments, including Gyp-Crete, are a critical component in all of these fire ratings.
  • Fiberboard does not contribute to fire ratings; it has a Flame Class Rating of III (or C), which means it is the highest class for flame spread. Gypsum underlayments are a Class A, meaning 0 flame spread.

    Indoor Air Quality
  • A common myth promoted by the fiberboard industry is that gypsum underlayments introduce significant amounts of moisture into the building envelope, leading to respiratory problems and mold growth. In truth, Maxxon underlayments and sound mats meet the stringent VOC requirements of GREENGUARD Gold Certification, are inorganic and provide no source of nutrients to sustain mold growth, making them safe for occupants of any age or sensitivity.

    For additional information, or to learn more about Maxxon underlayments or sound control systems, please contact your Regional Manager at 800-356-7887 or