Hardwood over Concrete: Technical Installation Solutions for Urban Homes

The rise of modern, urban housing in Bellevue has made concrete slab foundations common in condos, townhomes, and custom builds a frequent challenge for hardwood installation. Concrete slabs present a unique set of obstacles: primarily, the potential for moisture vapor transmission (MVT) and the rigid, cold nature of the subfloor. Traditional solid hardwood cannot be safely installed over concrete. The successful installation of hardwood over a concrete slab requires specific technical solutions, including the critical use of a high-quality moisture barrier and the mandatory selection of glue-down or floating engineered systems.

Carpet To Go serves homeowners, contractors, and businesses across the Puget Sound, specializing in technical installations. Our teams of professional installers and estimators ensure the highest quality of workmanship in an efficient manner, using proven methods and products to make your hardwood project over concrete a success.

The Concrete Slab Challenge: Moisture Vapor Transmission

The primary threat to any wood floor installed over concrete is moisture even if the slab appears dry.

Vapor Drive and Hardwood Failure

• Hygroscopic Nature: Concrete is porous and naturally wicks moisture from the ground below (a process known as vapor drive). This moisture travels up through the slab and, if not blocked, is absorbed by the hardwood.
• The Failure Point: When traditional solid hardwood absorbs this excess moisture, it swells, leading quickly to cupping, warping, and outright buckling of the floor a catastrophic installation failure.
• Moisture Testing is Critical: Prior to any hardwood installation, installers conduct thorough moisture vapor emission rate (MVER) testing of the slab using the Calcium Chloride or RH In-Situ Probe test. These tests determine the amount of protection needed.

The Engineered Solution: Structure and Stability

Because engineered hardwood is dimensionally stable and less prone to moisture-induced movement than solid wood, it is the only safe option for concrete installation.

Mandatory Moisture Barriers and Installation Methods

• The Moisture Barrier: A moisture barrier is not optional; it is the most critical element of the installation. Depending on the MVER test results, this barrier can be a specialized, 100%-solids polyurethane adhesive (which acts as a glue and moisture barrier in one), or a heavy-duty, impermeable vapor barrier film placed under the floor.
• Glue-Down Engineered System: This is a highly recommended method, especially for larger urban spaces. The engineered planks are secured directly to the concrete using a high-performance adhesive that often incorporates a moisture barrier. This provides a very stable, quiet, and solid feel underfoot.
• Floating Engineered System: In this method, the engineered planks are clicked together and rest on top of a foam or cork underlayment, which often incorporates the vapor barrier. The floor “floats” over the slab, allowing for natural movement without restraint. This is a fast, often quieter, and cost-effective option for many Bellevue condos.
• Acclimation: Even with a moisture barrier, both the engineered hardwood and the concrete slab must be properly acclimated to the interior’s temperature and humidity levels before installation begins.

Subfloor Preparation and Lifelong Maintenance

Proper preparation of the concrete surface is essential for the success of glue-down and floating systems.

Leveling and Long-Term Care

• Leveling and Flatness: Concrete slabs are rarely perfectly flat. Before installation, the slab must be ground down or patched with a self-leveling underlayment (SLU) to meet the strict flatness requirements of the hardwood manufacturer. Unevenness can cause stress on the joints of the hardwood, leading to squeaks or separation.
• Underlayment Choice: For floating floors, the choice of underlayment is crucial. Options include foam (basic sound dampening) or cork (superior sound dampening and thermal insulation, highly desirable for second-floor condos).
• Radiant Heat: If the concrete slab contains a radiant heating system (common in modern builds), engineered hardwood is the only viable option. The moisture barrier is still necessary, and the heat system must be controlled to prevent the surface temperature from exceeding manufacturer limits.

Technical Expertise for Hardwood over Concrete with Carpet To Go

Successfully installing hardwood over a concrete slab requires technical expertise, specialized materials, and rigorous testing a level of detail that only professional installation teams, like ours at Carpet To Go, can reliably provide. Carpet To Go has been helping homeowners and contractors for over thirty years; our friendly, knowledgeable staff and expert installation teams are dedicated to making your unique project a success.

To ensure your hardwood installation over concrete is performed correctly with the necessary moisture protection, visit our Bellevue, WA showroom or Contact us for an In-Home Consultation with a Design Consultant.