When it comes to building construction, there are a lot of moving parts that contribute to successful product and system installations. The “first side of your building envelope” — the system that separates the concrete slab you cast on or below grade from the under-slab environment — is no different; it is vital to the longevity and integrity of the building’s foundation. Since 1998, Stego has focused on providing high-quality materials and unsurpassed support to project teams in order to help protect all elements and people within the building envelope.
That’s why Stego Wrap Vapor Barriers and Retarders are the most widely specified below-slab moisture vapor protection films in North America. Our products’ unique combination of strength, resistance to water vapor permeation, and longevity— and the robust quality control measures we have implemented to verify these features — have contributed to that lofty title, as have Stego’s Life of the Building Warranty and unparalleled project-specific site support.
Selecting the right vapor barrier for your project is the first half of the battle. Then secondly, proper installation is equally important to help ensure your selected products perform. Throughout my career in the construction industry, I have seen a wide range of project conditions lending to diverse installation scenarios and have spent countless hours (quite an understatement) reviewing these various installation conditions to instill confidence in the builder, architect, and owner.
Based on my research in building science, expertise in product development, and deep understanding of the requirements of ASTM E1643 Standard Practice for Selection, Design, Installation, and Inspection of Water Vapor Retarders Used in Contact with Earth or Granular Fill Under Concrete Slabs —a best-practices guide developed over more than two decades — I am here to provide you with expert step-by-step instructions for an effective vapor barrier installation that will make your project a success.
START TO FINISH: Varies based on project size and number of installation crew members
DIFFICULTY: Easy to moderate; depending on project-specific conditions
INVOLVES: Lifting, cutting, taping, and kneeling
TOOLS:
MATERIALS:
Watch our video for a step-by-step guide on how to install an under-slab vapor barrier using Stego products.
A vapor barrier can be installed over an aggregate, sand, or tamped earth base. A cushion layer or sand base is typically unnecessary when using high-performance products — the vapor barrier is tough enough to withstand rugged construction environments.
Ensure the vapor barrier is clean and dry when applying a manufacturer’s engineered seaming tape or approved method.
Pro Tip: Use a cloth or other means to remove dust, debris, and excess moisture from the vapor barrier prior to applying seaming tape.
Where to terminate the vapor barrier can differ from job site to job site. Talk with any Stego Representative, and we will always recommend that you consult with the project design team about where to terminate the vapor barrier to ensure vapor protection is located where it is needed. This collaboration will help establish a balance between protecting as much of the building foundation as possible with the vapor barrier coverage, while also avoiding having the vapor barrier potentially compromise any structural considerations that may require bonds between the slab and the earth or other concrete surfaces.
ASTM E1643 instructs to extend the edges of the vapor barrier to terminate at one of the following locations:
For the remainder of this article, I will refer specifically to Stego’s diverse product offerings.
The first two scenarios described here utilize Stego Crete Claw Tape, a multi-layered tape that mechanically fastens the vapor barrier to the fresh concrete subsequently cast against it. Sealing with this accessory is the most selected method because of its ease of application and versatility to accommodate most conditions.
SECURING STEGO CRETE CLAW TAPE ON HORIZONTAL PERIMETER EDGES:
Pro Tip: Applying Stego Crete Claw Tape within 2” of the terminating edge is almost always possible, even when the terminating edges are not cut perfectly straight.
Pro Tip: Install Stego Crete Claw Tape before rebar but after the vapor barrier is sealed at the seams with seaming tape, sealed at penetrations, and terminated at the project’s perimeter and/or other specified terminating location.
Pro Tip: Temporarily secure the vapor barrier to the foundation wall with a small piece of seaming tape. Trim excess seaming tape after concrete placement and before removal of any adjacent forms.
Pro Tip: Clean the surface of the vapor barrier to ensure that it is free of moisture and debris prior to the installation of Stego Crete Claw Tape.
Where adjacent and existing foundation constructions exist (e.g., stem wall, footing), an alternative to using Stego Crete Claw Tape to seal the wrap’s terminating edges is to use a double-sided tape, like StegoTack Tape. A double-sided adhesive strip can be used to bond and seal the vapor barrier to concrete, masonry, wood, metal, and other surfaces. StegoTack Tape is a flexible and moldable material to allow for a variety of applications and installations.
SECURING STEGOTACK TAPE ON VERTICAL PERIMETER EDGES:
Pro Tip: Store StegoTack Tape in a cool area out of direct sunlight, and whenever possible, minimize the time that elapses between applying the StegoTack Tape to the existing wall and applying the vapor barrier to the StegoTack Tape.
Pro Tip: If consistent, continuous pressure will not be applied (e.g. by a concrete slab), a PVC termination bar, like Stego Term Bar, may be necessary.
And if that is not enough, here’s yet another alternative method for sealing the vapor barrier at the perimeter to existing adjacent concrete constructions, this time via a mastic-type sealant like Stego Mastic.
SECURING STEGO MASTIC ON EITHER VERTICAL OR HORIZONTAL EDGES:
Pro Tip: If consistent, continuous pressure will not be applied (e.g. by a concrete slab), Stego Term Bar may be necessary.
The purpose of a high-performance vapor barrier is to stop water vapor and other soil gases from migrating into the concrete slab and building interior. For that reason, imagine taking a bird’s eye view of the project – you want to make sure none of the subgrade is visible, and that’s true around permanent penetrations too (including the underside of horizontal utility penetrations).
Some projects are littered with clusters of pipes and other conduits (e.g., hospitals, laboratories, data centers) while others are mostly bare (e.g., warehouses). Many fall somewhere in between, and it is a rare project indeed that doesn’t have at least a few permanent penetrations of the vapor barrier. Here’s how to address those penetrations.
SEALING AROUND SINGLE PIPE PENETRATIONS:
IF VOID SPACE BETWEEN THE VAPOR BARRIER AND THE PIPE CAN'T BE MINIMIZED:
Pro Tip: Apply using a disposable glove, paintbrush, or similar.
SEALING AROUND MULTIPLE PIPE PENETRATIONS:
WITH TAPE:
While Stego Wrap Vapor Barriers and Retarders are extremely durable, the controlled chaos of a construction site can lead to damage to the vapor barrier during installation. It’s a good idea to review the vapor barrier coverage area for any damaged areas.
Also, be aware that work not yet performed by other trades could also cause damage to the vapor barrier. Slab reinforcing (rebar or mesh), as well as general machine and foot traffic, could lead to punctures or damage to the vapor barrier.
Pro Tip: Keep a roll of tape and some extra material on hand to touch up the vapor barrier all the way up to and through concrete floor placement.
Here are more specific steps: