Correct Moisture Barrier Under Wood Floors on Concrete

Installing beautiful wood floors is a dream for many homeowners. But this dream can quickly turn into a nightmare if moisture issues arise, causing cupping, warping, gapping, and other problems.

Concrete slab moisture is enemy number one for wood flooring. If excess moisture exists under new flooring, major damage occurs over time. Using a proper moisture barrier between concrete and wood is crucial.

Importance of Moisture Barrier Under Wood Floors

Why is controlling concrete moisture so vital under wood flooring? What issues can arise without taking proper precautions?

Preventing moisture damage to wood floors

Wood naturally expands and contracts with changes in moisture and humidity. Exposed to excess moisture, wood cupping, crowning, and warping occur as the material swell and distort.

Water causes wood floor finishes to peel and flake. It leads to decay and compromised structural integrity. A moisture barrier protects against moisture penetration, preserving the beauty of natural wood.

Allowing proper concrete curing

New concrete slabs contain substantial moisture, requiring full curing before installing wood flooring. Proper curing takes at least 60 days. Quick installation without a moisture barrier risks major floor damage.

A barrier allows concrete to cure fully while protecting wood from residual moisture. Test slab moisture content beforehand per concrete moisture testing standards for assurance.

Meeting installation requirements

Most engineered and solid hardwood flooring manufacturers require installing a moisture barrier over concrete subfloors. Failing to include a protective barrier according to guidelines voids the flooring warranty.

A proper moisture barrier meets manufacturer specs for material type, thickness, coverage, seam sealing, and permeance rate. Review standards before purchasing materials.

Extending flooring lifespan

Excess moisture threatens floor finishes, adhesives, and the stability of flooring materials. The useful life of expensive wood flooring becomes severely shortened without a functional shield.

An effective barrier adds longevity, preserving beautiful floors for decades rather than a few short years. This protection allows enjoying wood flooring investments much longer.

Choosing Right Moisture Barrier Material

What moisture barrier options work well for wood flooring over concrete? Consider all material aspects when deciding.

Polyethylene Plastic Sheeting

6 mil polyethylene plastic ranks among the most common moisture barriers. It comes in large sheets, overlapped atop concrete for a continuous protective layer from moisture penetration.

Plastic sheeting works well under engineered, solid, and laminate floating floors. Adhesive helps secure seams during installation. Apply tape for added seam strength if desired.

Foam Underlayment with Moisture Barrier

Many foam underlayments combine cushioning with an attached or embedded plastic moisture barrier. These two-in-one products reduce installation steps.

Foam underlayments work with floating click-lock floors, adding softness and sound isolation. Types include dense rubber, cork, and cross-linked polyethylene options in various thicknesses.

Rubber Cork Underlayment

Rubber granule and cork blended underlayments offer moisture protection plus antimicrobial and acoustic abilities. These green products rank as durable and sustainable.

High-quality rubber cork barriers resist mold, mildew, and decay while blocking up to 10 lbs. of moisture vapor emission. Density varies by brand and product tier.

Asphalt Saturated Felt Paper

Asphalt or tar coated felt paper makes an inexpensive moisture barrier option. It comes in long rolls, installed atop slabs prior to nailing down solid strip or plank floors.

Felt paper works under plywood subfloors as added protection from below. Overlapping creates a moisture shield that also reduces squeaks and board movement.

Installation Preparation

Proper planning and testing set the stage for an effective moisture barrier installation. Advance steps bring peace of mind before laying floors.

Testing Concrete Slab Moisture

Evaluate concrete moisture before the install using relative humidity testing per ASTM F2170. Measure levels with probe sensors at 20 different spots across the slab.

Concrete should emit less than 75% RH before installing wood flooring without a vapor retarder. Emissions up to 90% RH allow a barrier.

Allowing Adequate Concrete Curing Time

Ensure concrete cures adequately as excess moisture gets trapped beneath floors. New concrete requires about 60 days to dry sufficiently in most climates.

An effective moisture barrier protects wood flooring if concrete slab moisture remains slightly high after the cure. Test again before installing flooring.

Checking for Cracks and Uneven Surfaces

Inspect concrete for cracks, holes, and uneven spots needing repair. Grind down high points over 1/4 inch displacement. Fill divots and cracks with patching compound.

An uneven slab telegraphs issues through to the finished floor. Fix defects so the moisture barrier lies completely flush to the concrete.

Cleaning and Clearing Debris

Ensure the concrete slab appears free of dirt, oils, paint, drywall mud, or other construction debris. Sweep and mop areas well after surface repairs conclude.

Contaminants on concrete interfere with moisture barrier sheet adhesion. A clean, cleared subfloor allows proper product bonding.

Installation Steps

Follow precise moisture barrier directions for secure moisture protection under wood floors.

Roll Out Moisture Barrier Material

Roll out the plastic sheeting, underlayment, or felt paper parallel to the flooring installation direction per layout plans.

Run materials at least 4-6 inches up perimeter walls. Allow ample overlap for adhesion at seams to prevent moisture ingress.

Overlap Seams 2-4 Inches

Overlap moisture barrier edges and ends by 2-4 inches for continuity. Alignment keeps seams tight and staggered across the floor area.

Manufacturer guidelines detail the ideal overlap width for each product type. Following specs prevents leaks through slight edge gaps.

Seal Seams and Penetrations

Run clear packaging or duct tape along the entire moisture barrier perimeter and over all seams between sheets. Use acoustical sealant to seal around pipes and other penetrations.

Sealing safeguards against moisture sneaking under taped edges or through unprotected gaps. It enhances the barrier performance.

Install Flooring Above

Carefully install engineered wood, solid strips, or laminate flooring over the secured moisture retarder according to standard methods.

Glue down systems attach right to the barrier. Floating floors incorporate foam underlayment over the plastic layer as a combined package.

Problems and Solutions

What moisture related issues arise under wood flooring? Fixes bring floors back to normal.

Preventing Moisture Issues Under Wood Floors

Routinely checking under baseboards for condensation or water beads helps detect leaks early. Address rising slab moisture before it damages floors.

Sealing concrete cracks annually prevents moisture intrusion from below. Reapply floor protection after remodeling or water incidents.

Repairing Moisture Damaged Wood Floors

Pull up cupped planks to the nearest walls and replace affected areas. Sand and refinish mildly swollen sections to restore flatness.

For extreme water damage, a full floor replacement works better than continual repairs. Include an enhanced vapor barrier during reinstallation.

Identify moisture sources causing wood floor deformities. Boost room ventilation, seal slab cracks, or improve drainage against foundation walls as needed.