Gypsum underlayments are becoming increasingly popular among contractors, yet they also present several challenges in the flooring industry. As a lighter, more affordable alternative to traditional concrete, gypsum is gaining traction in modern construction, especially for multi-family housing, apartments, and hotels. While it offers a range of benefits like fire resistance, sound control, and durability, dealing with gypsum underlayments requires special care and attention.
What Are Gypsum Floor Underlayments?
Gypsum floor underlayments are non-structural, poured materials designed to create a smooth, flat surface for finished flooring. They are particularly valued for their fire-resistant properties and ability to control sound. Additionally, gypsum underlayments are lighter than traditional concrete, making them easier to handle and install. For example, a 1.5-inch slab of gypsum concrete weighs 13 pounds per square foot, while regular concrete weighs 18 pounds per square foot. Despite this difference, gypsum underlayments offer comparable compressive strength to traditional concrete, making them a versatile choice for residential and commercial projects.
A popular brand of gypsum underlayment is GypCrete, a product by Maxxon Corporation. Gypsum underlayment is also produced by other suppliers, including Hacker Industries, each offering various products for different construction needs. These materials are commonly used in environments where fire protection and soundproofing are priorities, such as in hotels, multi-family housing, and large apartment complexes.
The Installation Process
Installing a gypsum floor underlayment involves several steps and conditions to ensure a smooth and successful installation. Before, during, and after installation, the building interior must be properly enclosed and maintained at a temperature above 50°F. This is critical for stabilizing the structure and subfloor temperatures. Additionally, continuous ventilation is required to remove moisture from the area, ensuring that the gypsum dries properly. Adequate heating and ventilation are essential to achieve the best drying conditions for the gypsum underlayment.
Ventilation and Drying Conditions
The drying time for gypsum underlayments can vary depending on multiple factors, including ventilation, humidity levels, weather conditions, and the thickness of the applied gypsum layer. Ideally, with proper ventilation and heating, a gypsum topping installed at 3/4 inch thickness should take approximately 7 to 10 days to dry completely. However, under less-than-ideal conditions—such as low temperatures, high humidity, or poor ventilation—the drying time can be extended.
To achieve the proper drying environment, it is essential to monitor the air exchange and maintain the necessary temperature in the building. During this drying phase, the gypsum underlayment must be protected from excess moisture, as excessive water can lengthen the drying time significantly. If natural ventilation is insufficient, mechanical ventilation or additional heating may be required to accelerate the drying process.
Testing for Dryness
Before any flooring coverings are installed over a gypsum underlayment, it is crucial to ensure the material is completely dry. The moisture content of the gypsum must be below 5% for optimal results. One of the most reliable methods for measuring gypsum moisture content is using a moisture meter designed specifically for gypsum, such as the Delmhorst BD-2100 or Delmhorst G-79.
However, a significant challenge arises when dealing with resilient flooring like vinyl, as flooring manufacturers often do not recognize moisture meter tests as adequate for vinyl flooring. The ASTM F2170 standard, which involves using the Insitu RH Probe Test, is an acceptable method for testing the moisture content in gypsum toppings. Unfortunately, this test is difficult to perform properly on thin gypsum layers, such as those found on wood subfloors (minimum thickness of 3/4 inch) or concrete subfloors (minimum thickness of 1/2 inch). In such cases, accurate moisture readings may be hard to obtain, and as such, additional testing methods may be necessary.
Sealing the Gypsum Surface
One of the unique challenges of working with gypsum underlayments is the necessity of sealing the surface. Unlike concrete subfloors, where adding a sealer may break the bond with adhesives or patching compounds, gypsum surfaces require a Top Coat or Sealer after installation. This layer serves two purposes: it enhances the bond between the gypsum and the adhesive and prevents dusting, which can negatively affect the adhesive’s performance.
It is essential to ensure the gypsum surface is clean, dry, and free of contaminants such as mud, oil, or grease before applying the Top Coat/Sealer. The sealing process is particularly crucial because the porosity of the gypsum can significantly affect the drying rate of adhesives. If the surface is porous and unsealed, it can reduce the open time of adhesives by as much as 50%, making installation challenging.
A practical test to determine whether the gypsum surface is properly sealed is to sprinkle water onto the surface. If the water is absorbed quickly, it indicates that the surface is still porous, and an additional coat of sealer is required. Conversely, if the water beads up on the surface, it signifies that the gypsum is adequately sealed, ensuring that the adhesive will have its full working time.
Bonding Issues with Resilient Flooring
The adhesion between the gypsum surface and the resilient flooring material is another critical factor to consider. Inadequate bonding can result in floor instability and premature wear. To ensure proper adhesion, a bond test should be conducted by installing a 3-foot by 3-foot section of flooring using the recommended adhesive in different areas of the room. These test areas should be spaced approximately 50 feet apart, ideally in low-traffic areas such as near walls or columns. After 72 hours, the flooring should be securely bonded, indicating that the subfloor surface is clean and properly prepared for flooring installation.
Conclusion
While gypsum floor underlayments offer many advantages, including fire resistance, sound control, and a lightweight alternative to traditional concrete, they require careful handling during installation. The key to successful gypsum underlayment installation is ensuring proper ventilation, maintaining an appropriate temperature, and testing for adequate moisture levels before proceeding with flooring installation. Additionally, sealing the gypsum surface and conducting bond tests for adhesives are crucial steps to ensure long-lasting performance and a smooth finish for resilient flooring.
By taking these factors into account and following industry best practices, contractors and homeowners can successfully install resilient flooring over gypsum underlayments, resulting in durable and aesthetically pleasing floors that stand the test of time.