Below the Surface

April 5, 2005
Exploring enhancements in poured cementitious underlayment
While building owners, architects, and builders can choose from a wide variety of underlayment materials to protect commercial floors, they increasingly have made poured cementitious gypsum their material of choice. Technological advancements in this underlayment’s strength, fire resistance, and sound insulation, along with its ability to be poured prior to the installation of drywall, make it advantageous for use in both dry and wet areas.Typically, poured cementitious underlayments are installed over a wood or concrete subfloor and then covered with floor finish materials such as vinyl, wood, tile, or carpet.  Some systems also have been specifically designed for use over electrical and hot-water radiant flooring tubes.The quality of poured cementitious underlayments has improved over the past several years.  Some systems offer strengths ranging from 2,500 to as much as 8,000 psi – the highest available. At these strengths, they are 50-percent more durable than entry-level poured underlayments.Underlayments at 6,000 to 8,000 psi may become the base of a finished floor that can be decorated in an unlimited range of colors and patterns to create a unique, high-end look. This enhanced performance has now made poured cementitious underlayments appropriate for virtually any commercial project.Moreover, the underlayments are suitable as a major component in sound systems designed to meet or exceed today’s stricter building code requirements. Some even meet Underwriters Laboratories’ designs for fire and sound ratings.Recently, surface enhancers have been developed that strengthen the bond between adhesives and poured underlayments. Along with mold and mildew resistance, these coatings also are pH-compatible with most water-based adhesives, and reduce the alkalinity of concrete floor surfaces without adversely affecting the floorcovering adhesive. Fast-drying and economical, the surface enhancer can be rolled or spray-applied as soon as the underlayment is walkable – usually within about 4 hours.Poured cementitious underlayments provide practical advantages as well. They can reduce the overall construction schedules while working more efficiently and safely. Today, underlayments with low water demand and a minimum compressive strength of 2,500 psi are able to withstand the rigors of construction activities. As crews go about their jobsite business, the floors are less prone to dusting, chipping, and cracking.When the underlayment is poured immediately after “dry in” (after the structure is secure from moisture), contractors are able to take advantage of significant scheduling benefits. By achieving 80 percent of its compressive strength within 24 to 36 hours following application (with proper ventilation), a 0.75-inch-thick floor can dry completely in 5 to 7 days.Reducing moisture that might promote the growth of mildew is also a top priority for building owners. The earlier installers pour the underlayment, the longer the drying time – and the less opportunity for moisture to be present during subsequent construction phases. In addition, a dry surface eliminates the possibility of cementitious flooring materials spattering on gypsum wall surfaces and damaging finished walls.Finally, pouring prior to the installation of drywall adds a new safety dimension to the jobsite. Providing a high-strength, smooth floor surface greatly reduces the chance of injuries that can occur when walking or moving equipment across uneven surfaces. These beneficial advancements, along with new innovations currently on the horizon, definitely make it worthwhile to take a second look at poured cementitious gypsum underlayments.Ray Kaligian is director of marketing, specialty products division, United States Gypsum Co. (, Chicago, a leading manufacturer of industrial products used in a variety of applications.

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