When constructing a building in the U.S., one of the most critical yet often overlooked components of the building envelope is the under-slab vapor barrier. This protective layer prevents moisture from rising from the ground into the concrete slab and ultimately into the interior of the building. Proper installation of a vapor barrier is essential for preserving the integrity of flooring systems, preventing mold and mildew growth, and ensuring the long-term durability of the structure.
Stego Industries, a leading provider of vapor barrier solutions since 1998, offers a range of high-performance products designed for under-slab applications. The company’s Stego Wrap Vapor Barriers and Retarders are widely used in North America due to their durability, resistance to water vapor permeation, and comprehensive support for project teams. This article outlines the detailed installation procedures for Stego’s under-slab vapor barrier products, based on the manufacturer’s official documentation and best practices.
The guidance provided below is intended for U.S. construction professionals, including contractors, engineers, and DIY builders, who are responsible for installing under-slab vapor barriers on residential or commercial projects. The steps are designed to ensure compliance with industry standards, such as ASTM E1643, and to maximize the effectiveness of the vapor barrier system.
Preparing for Vapor Barrier Installation
Before beginning the vapor barrier installation, it is essential to gather the necessary tools and materials and prepare the sub-base according to the specifications provided by the design professional.
Tools and Materials Required
The following tools and materials are typically required for the installation of an under-slab vapor barrier using Stego products:
Tools:
- Utility knife or scissors
- Tape measure
- Work gloves
- Work boots
- Protective eyewear
- Trash/recycling bags
- Towel or rag
- Knee pads (optional)
- Tape roller (optional)
- Bulk sausage or caulking gun (depending on the installation method)
Materials:
- Vapor barrier or vapor retarder
- Vapor barrier seam and sealing tape
- Accessories for sealing the perimeter and penetrations, such as:
- Stego® Crete Claw® Tape
- StegoTack® Tape
- Stego® Mastic
Sub-base Preparation
The vapor barrier can be installed over an aggregate, sand, or tamped earth base. A cushion layer or sand base is typically not required when using high-performance vapor barriers, as the material is designed to withstand the rigors of the construction environment.
Once the base is prepared according to the design professional’s specifications, the vapor barrier can be unrolled and positioned over the area where the concrete slab will be placed. It is important to ensure that the vapor barrier completely covers the placement area and that all joints or seams are overlapped by at least six inches.
Step-by-Step Installation Process
1. Unrolling and Positioning the Vapor Barrier
The first step in the installation process is to unroll the vapor barrier over the prepared sub-base. The vapor barrier should be unfolded to completely cover the area where the concrete slab will be cast. Overlapping all joints and seams by a minimum of six inches is essential to ensure a continuous barrier against moisture vapor.
It is important to avoid unnecessary creases or folds in the vapor barrier, as these can lead to weak points that may compromise the effectiveness of the system. If the vapor barrier is not perfectly cut to fit the dimensions of the slab, it should still be overlapped at the edges to maintain continuity.
2. Sealing Joints and Seams
Once the vapor barrier is in place, the next step is to seal all joints and seams to prevent moisture from bypassing the barrier. This is typically done using Stego seam sealing tape, which is designed to adhere securely to the vapor barrier material.
To seal the seams:
- Apply the seam tape over the overlapped area, ensuring that it covers both layers of the vapor barrier.
- Press the tape firmly into place to ensure a strong bond.
It is also important to inspect the vapor barrier for any small holes or slices that may have occurred during installation. For minor damage, center the seam tape over the affected area and press it into place. For larger holes or slices, a patch should be applied by cutting a piece of the vapor barrier to cover the damaged area with a six-inch margin on all sides and sealing it with seam tape.
3. Sealing Penetrations
In many construction projects, utility penetrations such as pipes and conduits pass through the concrete slab. These penetrations must be properly sealed to maintain the integrity of the vapor barrier.
For single pipe penetrations:
- Cut a slit in the vapor barrier to accommodate the pipe.
- Seal the pipe individually using seam tape to ensure there are no exposed edges of the vapor barrier.
For multiple pipe penetrations:
- Cut a slit large enough to accommodate all pipes.
- Seal each pipe individually using seam tape.
- If the pipes are too close together for effective tape sealing, use Stego Mastic to seal the void space between the pipes.
Mastic should be applied using a disposable glove, paintbrush, or similar tool to ensure that the entire void space is sealed. It is important to ensure that no unsealed path exists to the subgrade, as this would compromise the effectiveness of the vapor barrier.
4. Securing the Perimeter
Securing the perimeter of the vapor barrier is essential to prevent it from shifting during the concrete placement process. Stego offers two primary options for securing the perimeter: Stego Crete Claw Tape and StegoTack Tape.
Using Stego Crete Claw Tape on Horizontal Edges
- Apply the entire three-inch width of Stego Crete Claw Tape as close as possible to the terminating edge of the vapor barrier.
- Ensure that the tape is not hanging off the edge of the barrier or applied to another surface.
- The entire width of Crete Claw should be applied to the vapor barrier.
- It is typically possible to apply the tape within two inches of the terminating edge, even if the edge is not perfectly straight.
Using StegoTack Tape on Vertical Edges
- Remove the release liner on one side of StegoTack Tape and stick it to the foundation wall at the height of the slab or at any impediments.
- When ready to apply the vapor barrier, remove the exposed release liner from the double-sided tape.
- Press the vapor barrier firmly against the StegoTack Tape to secure it.
- Trim any excess seaming tape after concrete placement and before the removal of any adjacent forms.
Additional Tips
- Stego Crete Claw Tape should be installed last, after the vapor barrier is sealed at the seams with seaming tape and at penetrations.
- Ensure that the surface of the vapor barrier is clean and free of moisture and debris before applying Stego Crete Claw Tape or StegoTack Tape.
Final Inspection and Concrete Placement
Before proceeding with the concrete placement, it is crucial to conduct a thorough inspection of the vapor barrier to ensure that all seams, penetrations, and perimeter edges are properly sealed. Any damaged areas should be repaired immediately using the appropriate sealing methods described above.
Stego recommends keeping a roll of seam tape and extra vapor barrier material on hand throughout the installation process to address any issues that may arise. It is also important to review the project plans and specifications to ensure full compliance with the design professional’s requirements.
Once the vapor barrier is fully installed and inspected, it is time to call for the concrete. The vapor barrier is now in place to protect the building from moisture infiltration and to support the longevity of the flooring and other building materials.
Conclusion
Proper installation of an under-slab vapor barrier is a critical step in the construction process that ensures the long-term durability and comfort of the building. Using high-quality materials such as Stego Wrap Vapor Barriers and following a structured, step-by-step installation process are essential for achieving a continuous, effective moisture barrier.
The key steps in the installation process include: preparing the sub-base, unrolling and positioning the vapor barrier, sealing joints and seams, sealing penetrations, securing the perimeter, and conducting a final inspection before concrete placement. By following these steps and using the appropriate sealing and securing products, construction professionals can ensure that the vapor barrier performs as intended.
It is important to consult with the design professional, review project specifications, and follow industry standards such as ASTM E1643 to achieve full compliance and optimal performance. With the support of Stego’s technical resources and on-site project assistance, construction teams can confidently install vapor barriers that protect the building for years to come.