Knowing the individual qualities of commonly used flooring underlayments (namely wood, fiber-reinforced gypsum panels, poured cementitious underlayment and cement board) will help you install aesthetically pleasing and long-lasting floors.
Because wood-based underlayments are relatively inexpensive, they remain the most commonly used underlayment material. Whether you choose OSB (oriented strand board), particle board, composite panels, plywood or lauan, you may find that these materials have limitations, especially in areas that are subject to moisture, such as kitchens, mud rooms, entry foyers and bathrooms.
While wood is acceptable under surfaces such as carpeting, it may create finishing problems when used under vinyl floor coverings. Many wood-based products are dimensionally unstable, making them less than ideal for use with ceramic tile. When wood is used under ceramic tile systems, delamination or broken tiles can occur. Additionally, when wood-based substrates are exposed to moisture, they can swell and warp, causing deterioration of the adhesive and damage to the underlayment.
In response, several alternatives have been developed that not only solve these problems, but provide additional strength and water resistance as well.
Fiber-reinforced gypsum panels provide a versatile, economical and environmentally friendly alternative to wood. The panels are well-suited for use in both wet and dry environments, including kitchens, bathroom floors, and tub and shower enclosures. They can be used underneath a variety of surfaces, including ceramic tile and vinyl floors.
While fiber-reinforced gypsum underlayment is a versatile backer board for use primarily under ceramic tile and vinyl, it can also be finished like drywall. This revolutionary product family incorporates 95-percent recycled materials and has earned "Green Cross" certification. It is an excellent replacement for lauan, which is made from wood harvested in endangered old-growth forests. Consequently, fiber-reinforced gypsum products are proving to be especially attractive for environmentally conscious specifiers, builders, contractors and building owners.
The rough surface of some wood-based products may eventually show through vinyl. To remedy this problem, contractors often will install a 1/4-inch-thick lauan underlayment.
Because fiber-reinforced gypsum panels deliver up to 60 percent more indentation-resistance than traditional underlayments such as OSB, contractors do not need to reinforce it. The board's impact resistance ensures a smooth, flat surface with no bumps or ridges to telegraph through the vinyl. Fiber-reinforced gypsum underlayment also contains no resins, adhesives, solvents or dyes that can stain floor-covering materials.
The behavior of wood-based products can cause problems when they are exposed to moisture. Fiber-reinforced gypsum panels utilize a patented technology that provides moisture resistance throughout the entire panel, making them an ideal solution for wet areas where mold and moisture may become a potential problem. In fact, they score a perfect "10" - confirming no mold growth - when tested following American Society for Testing and Materials (ASTM) D3273-00 standards. The panels also resist swelling, warping and other moisture-related issues that can occur with products such as plywood, OSB and lauan.
Designed to be cut using a utility knife, fiber-reinforced gypsum underlayment installs quickly and easily simply by scoring and snapping the panels. The product is available in a variety of sizes and thicknesses.
Poured Cementitious Underlayments
Architects, builders and owners can choose from a wide variety of cementitious underlayments to protect residential, commercial, institutional and industrial floors. Technological advancements in lightweight, pourable gypsum cement's strength, fire resistance and sound insulation - along with its ability to be poured before drywall is installed - make it advantageous for use over both wood and concrete floors (and eliminate the need to shotblast concrete floors).
Typically, poured gypsum underlayments are installed over wood or concrete subfloors and then covered with floor finish materials. These systems deliver a smooth surface that sets quickly and provides a bondable underlayment for finishing with carpet, vinyl, ceramic tile and other floor coverings. Poured gypsum underlayments can be installed quickly (up to 30,000 square feet in a single day).
The quality of poured gypsum cements has improved over the past several years while the industry has simultaneously established ever-higher compressive strengths. Today, these systems can offer strengths ranging from 2,500 to as much as 8,000 psi.
In addition, some gypsum cements are even strong enough to act as a truly self-leveling floor. They may also become the base of a finished floor that can be decorated with a stain or coating in an unlimited range of colors and patterns to create a unique aesthetic appearance.
Another option is either poured portland or engineered cement underlayments. Portland cements have been popular for many years and are a very economical choice. Engineered cements incorporate a unique cement chemistry for users who prefer a cement-based underlayment. They can be used in a wide range of applications and provide the high compressive strengths, performance and versatility found in existing gypsum cements.
Engineered cements can also be formulated to provide self-drying characteristics. Some can be used in high-traffic areas (including warehouses) without the need for a surface coating.
Increasingly, poured underlayments are becoming a major component in sound-masking systems designed to meet or exceed today's building code requirements. Several systems also meet Underwriters Laboratories designs for fire and sound ratings.
Cement board offers many of the advantages of thick-bed cement mortar without the expense and lengthy installation process. The board consists of a cementitious substrate made from portland cement that is sandwiched between layers of inorganic fiberglass mat. Its inherent strength provides a water-resistant base for tiled surfaces, especially those exposed directly and repeatedly to moisture. It will not swell, soften, decay, delaminate or disintegrate when exposed to water.
Ceramic tile has long been popular and affordable, so protecting it with a high-performance substrate is an important step in keeping the tile looking good and lasting longer. Cement board helps eliminate the possibility of prolonged exposure to moisture harming the surface behind or underneath the tile. Plus, its alkaline nature does not support mold growth.
Sooner or later, moisture will find a way to seep through even the highest-quality tile installation. The wrong substrate could cause cracked or loosened tiles, warped or bulging surfaces and excessive mildewing. Because cement underlayment is made from cement, it is water-durable. Should water seep through the grout, the cement board won't buckle, swell or expand.
Easy to install, cement board is available in various panel sizes and thicknesses for use in bathtub and shower surrounds, as well as on floors.