Can you use self-leveling underlayment on wood?

Quick Answer

Yes, you can use self-leveling underlayment on wood substrates, but proper preparation is essential for good adhesion and to prevent moisture issues. The wood must be clean, dry, structurally sound, and properly primed before applying self-leveling underlayment.

Overview of Using Self-Leveling Underlayment on Wood

Self-leveling underlayment is a quick and easy way to create a smooth, flat surface prior to installing floor coverings like tile, vinyl, or laminate flooring. It can be poured or pumped onto surfaces like concrete, OSB, plywood, and even existing vinyl or wood floors. When applied to wood, there are some important factors to consider:

Types of Wood Subfloors

The two main types of wood subfloors are:

– Plywood – High quality, void-free plywood that is a minimum of 5/8″ thick is ideal for self-leveling underlayments. Look for a C-C plugged or better grade.

– OSB (oriented strand board) – OSB is prone to swelling and movement so it must be sealed properly. Use a minimum of 23/32″ thick OSB with a fully sanded face.

In general, plywood provides a smoother, more stable base than OSB.

Preparing the Wood Surface

Proper preparation is crucial when using self-leveling underlayment on wood:

– The wood must be structurally sound – Replace any areas that are damaged or not firmly attached.

– Clean thoroughly to remove dirt, oils, wax, sealers, paint, drywall mud, and other contaminants that can reduce adhesion.

– Sand down high spots and fill low areas with a polymer-modified self-leveling or patch underlayment.

– Seal the wood to prevent moisture absorption using an oil-based primer.

– Solid hardwood flooring requires sealing knots and dense species may need sanding for the primer to penetrate.

– Allow the primer to fully dry before applying self-leveler.

Preventing Moisture Issues

Unsealed wood can absorb water from self-leveling products leading to swelling, deterioration, and adhesion loss. Prevent this by:

– Ensuring the primer provides a waterproof seal to the wood substrate.

– Only applying self-leveler up to the manufacturer’s recommended thickness in a single pour (typically 1/4″ to 3/4″).

– Allowing proper drying time based on humidity levels before installing floor coverings.

– Using a moisture barrier over wood substrates can provide added protection.

Priming the Wood Surface

Priming is essential on wood before applying self-leveling underlayments. Be sure to use the proper type of primer:

– For plywood, use a PVA or latex primer.

– For OSB, use an epoxy or urethane primer to seal and waterproof.

– For dusty or porous substrates, prime first with a acrylic primer.

– Always follow the leveling product manufacturer’s recommendation for primer type.

Allow the primer to fully dry before pouring the underlayment. Be sure to apply an even coat, especially in grout lines on tile substrates.

Considering Floor Coverings

The type of flooring you plan to install is an important factor when applying self-leveler over wood:

– For natural stone, ceramic, porcelain, or glass tile, self-leveling provides an excellent base.

– Self-leveling underlayment must dry fully before installing vinyl, VCT, laminates, or carpeting.

– Hardwood flooring can be installed over self-leveler but may require a plywood layer on top for naildown installation.

– Self-leveling underlayment is compatible beneath floating engineered hardwood floors.

Always check the flooring manufacturer’s requirements before applying self-leveling underlayment.

Step-by-Step Process for Applying Self-Leveling Underlayment on Wood

Follow these key steps when using self-leveling underlayment on plywood or OSB substrates:

Step 1 – Inspect and Prepare the Wood Subfloor

– Inspect the wood for damage, soft spots, loose panels, or gaps. Repair as needed.

– Clean thoroughly – sweep, vacuum, mop, and degrease the wood surface.

– Check moisture content – wood should be no more than 12% moisture content.

– Sand down any high points and fill low spots with a patching compound.

Step 2 – Prime the Wood Substrate

– Apply primer according to manufacturer’s instructions for wood substrates.

– Allow primer to fully dry before applying self-leveler.

Step 3 – Mix the Self-Leveling Underlayment

– Mix self-leveling product per manufacturer’s directions.

– Only mix what can be applied during the open time (20-30 mins typically).

– For large areas, use pumping equipment to distribute the pour efficiently.

Step 4 – Pour or Pump the Self-Leveling Underlayment

– Pour self-leveling underlayment and spread into place using a gauge rake.

– Use a smoother to remove trowel lines and help level.

– Take care not to overwork the surface.

Step 5 – Allow Proper Curing Time

– Self-leveling underlayment typically cures in 2-3 hours for foot traffic.

– Allow 24 hours minimum for light traffic and floor coverings.

– Ensure moisture testing confirms dryness before flooring installation.

Step 6 – Install Floor Covering

– Once fully cured, the self-leveling underlayment provides a smooth, flat base for flooring.

– Always follow flooring manufacturer’s installation guidelines.

– Use proper adhesives, fasteners, or mortars suited for self-leveling underlayment.

Benefits of Using Self-Leveling Underlayment on Wood

There are several advantages to using self-leveling underlayment on plywood or OSB subfloors:

Smooths and Flattens

– Self-leveling compounds flow smoothly across the substrate.

– This helps correct minor imperfections or variations in the wood.

– Provides a flat, even base for flooring that improves aesthetics and performance.

Fast Installation

– Self-leveling underlayments can be installed very quickly compared to other smoothing methods.

– Large areas can be leveled in just a few hours.

– Speeds up overall installation time for new floor coverings.

Prevents Moisture Issues

– Properly sealed wood won’t absorb moisture from self-leveling pour.

– Limits swelling and cupping of wood from excess moisture.

Versatile for Many Flooring Types

– Suitable beneath a wide range of flooring materials.

– Provides appropriate substrate for tile, stone, vinyl, laminate, engineered hardwood, and carpeting.

Low Profile Application

– Can be applied in thin layers from 1/8″ to 1/2″ thick.

– Won’t raise floor height as much as other underlayment options.

– Allows installation of same floor height next to other rooms.

Challenges of Using Self-Leveling Underlayment on Wood

Despite the benefits, there are some potential challenges to consider when using self-leveling underlayment on wood:

Moisture Imbalance

– Unsealed wood can absorb water from the pour leading to swelling or cupping.

– Trapped moisture underneath flooring can cause mold, mildew, and adhesive failure.

Uneven Drying

– Variations in porosity or density of the wood can lead to uneven drying.

– Can result in cracks, hollow spots, or bond failure.

Excessive Thickness

– Applying self-leveling compound too thick in a single pour increases drying time.

– Thick layers are more prone to cracking shrinkage as the material dries and cures.

Inadequate Subfloor Prep

– Contaminants on the wood reduce adhesion with self-leveling underlayment.

– Cracks or imperfections telegraph through to the finished floor.

– Can lead to cracks, holes, bumps, and other application flaws.

Incompatible Materials

– Some coatings or adhesives react poorly with self-leveling products.

– Can cause bond failure, chemical reactions, staining, or compromised strength.

FAQs About Using Self-Leveling Underlayment on Wood

Can you put self-leveling underlayment over OSB?

Yes, self-leveling underlayment can be installed over OSB but the wood substrate requires sealing first with an epoxy primer to prevent moisture issues.

What can you not use self-leveling underlayment on?

Self-leveling underlayment should not be applied directly to surfaces like adhesive residues, gypsum-based products, chipboard, Lauan plywood, tempered hardboard, asbestos, aluminum, and dimensionally unstable materials prone to expansion or contraction.

How long does self-leveling underlayment take to dry before laying tile?

Most self-leveling products take 2-4 hours to dry for light foot traffic. However, allow at least 24 hours curing time before installing tile or floor coverings over the top. Check moisture levels to confirm it is fully cured.

Can self-leveling underlayment be used on stairs?

Yes, self-leveling underlayment can be applied to stair treads and risers to provide a smooth, consistent surface prior to installing flooring. Use with a primer and allow extended drying time.

Is self-leveling underlayment waterproof?

Self-leveling underlayments provide a water-resistant surface but are not entirely waterproof on their own. For waterproofing wood substrates, use a waterproof primer or membrane before the self-leveling pour.

Conclusion

Self-leveling underlayment is an excellent choice for smoothing and flattening wood subfloors prior to installing floor coverings. However, proper preparation and priming of the wood surface is vital for good adhesion and preventing moisture issues that could damage the wood over time. Provided the wood is clean, dry, structurally sound, and sealed from moisture, self-leveling underlayment can create the ideal substrate for long-lasting tile, vinyl, laminate, or hardwood floors on top. With the right product selection and application process, contractors can achieve professional, high-quality results.

Type of Wood Subfloor	Minimum Thickness	Primer Recommendation
Plywood	5/8″	PVA primer
OSB	23/32″	Epoxy primer