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Since the late 1970s, poured gypsum underlayments have played an important role in both the fire resistance and sound attenuation of multi-family dwellings. Regional building codes began to require floor-ceiling fire breaks around this time. Several methods were developed to provide this fire break, including gypsum-based and lightweight concrete products.
Both have the capability to be used as a heat sink, however, engineers and designers came to prefer gypsum underlayments because they can achieve fire ratings at half the thickness of lightweight concrete. The two can also provide adequate compressive strengths for use with many types of floor coverings. Unfortunately, over the next couple of decades, bad practices in the field led to gypsum underlayments with low compressive strengths while developing a reputation for being soft, chalky, and weak.
Gypsum floors with low compressive strengths persist today, especially when rehabbing older buildings. In the past, carpet and padding were popular floor coverings in multi-family units, which not only helped provide exceptional sound attenuation between units but also helped cover weak underlayments with minimal-to-no repairs. More recently, there’s been a trend in floor coverings in multi-family units from carpet to resilient flooring products. Installation of those resilient floor coverings requires a smooth, dense, and hard surface—meaning those old, damaged gypsum floors can no longer be hidden and must be properly repaired.
Maintaining the fire resistance of the existing structure is critical for code compliance and the safety of those in the building. Products used for repairing damaged gypsum floors should meet the ASTM E119/UL 263 standard for fire resistance. There are many products in the market that claim to be approved for repairing gypsum floors, and while there’s no doubt that many can provide a smooth and hard surface, their ability to provide the fire resistance necessary to maintain the fire rating of that floor-ceiling is certainly a cause for concern.
When it comes to repairing gypsum floors, the right products and proper procedures are the key to maintaining the fire rating and regaining the strength and durability needed to support high-performance floor coverings. One of the advantages of gypsum-based products is that they achieve all this and more. In most cases, they can be applied much thinner and still meet the standard for fire resistance. In most applications, the minimum thickness needed to meet the standard is 3/4 in. They are also quick-setting so trades can resume their work the following day and, when properly formulated, gypsum-based products can achieve compressive strengths as strong as concrete.
At USG, we have developed a portfolio of products and solutions for rehabbing damaged gypsum floors. Depending on the size of the repair, USG offers both a pourable and trowelable solution that can be used to rejuvenate a bad floor and provide a new, durable, smooth surface that is ready to receive today’s most demanding types of floor coverings.
USG DurockTM Brand Quik-TopTM is a self-leveling underlayment that self-seals and is ready for floor coverings in as little as 15 hours with a compressive strength of up to 10,000 psi. Similarly, USG DurockTM Tuf-SkimTM is a trowelable floor patch for smaller, well-defined areas of repair. It can be ready for floor coverings in as little as 30 minutes and has a compressive strength of up to 6,000 psi.
All USG gypsum-based underlayments and patches are UL Classified and specified for use in over 130 fire-rated assemblies where UL Designation Type LRK or HSLRK are listed. Before proceeding with any repairs, determine whether the assembly is structurally sound. Consult a structural engineer if there are any concerns about the integrity of any existing floor.
For more information about USG gypsum repair products and solutions, visit usg.com/repair