Engineered wood floor installation over concrete

For best results, several areas of each room should be tested for excess moisture. If tests indicate too much moisture is in the slab, do not install hardwood floors. A new moist slab should be allowed to dry naturally or the process can be hastened with heat and ventilation. Slabs less than 60 days old are generally too wet to install floors. Test for Dryness New concrete is heavy with moisture, and it must be a minimum of 30 days old before moisture testing begins.

Determining moisture content of both the wood flooring and the subfloor is an important part of quality control in the flooring installation process.

Detailed qualitative and quantitative testing methods are provided by the National Wood Flooring Association. Flat, Clean Slab The slab must be flat with a trowel finish, free of grease, oil, stains and dust. Grind off any high spots and fill any low spots. Vapor Retarder With solid hardwood floors, a proper vapor retarder must be installed on top of the slab to make sure normal slab moisture does not reach the finished floor.

Layers of asphalt felt with asphalt mastic or 6 mil polyethylene sheathing are some of the choices. Subfloors The National Wood Flooring Association recommends two choices in sub-flooring systems for concrete installations: plywood-on-slab and sleeper. Either subfloor system is satisfactory for three-quarter inch flooring.

Asphalt felt or building paper: first, prime the slab and apply cold, cut-back asphalt mastic with a notched trowel 50 sq. Allow to set for two hours. Unroll lb. Over this, apply a second similar coating of mastic and roll out a second layer of asphalt or paper in the same direction as the first, staggering the overlaps to achieve an even thickness. Polyethylene: Cover the entire slab with 4 to 6 mil polyethylene film, overlapping the edges 4" to 6", and allowing enough film to extend under the baseboard on all sides.

Gluing floorboards to the underlayment that sits on the concrete is not recommended. Most engineered wood floors manufactured today are the tongue and groove kind. The boards interlock with one another so that neither glue nor nails are required to keep them in place. By virtue of this interlocking, the boards become a single, large sheet.

This sheet sits on top of an underlayment to protect it from moisture that might come up from underneath it. Between the interlocking capability and the way engineered wood is made, this is the type of installation most recommended for engineered wood over concrete in basements especially.

This can be a godsend when it comes to basements where sounds tend to echo, amplify, and bounce around. The intended environment of the engineered wood floor should always be paid equal attention. A dehumidifier is a good way to do this. There is also the matter of ambient air temperature. It should be reasonably consistent and it should always measure between 60F and 80F. Some manufacturers suggest removing the boards from the packaging.

None advise against it. Racking is a term defined as the laying out of the floorboards in advance of the actual installation. Racking a floor also allows for any defective pieces to be withheld for return to the manufacturer.

For your concrete slab to function as a subfloor, holes, cracks, and low spots need to be patched. The subfloor also needs to be level for your engineered wood floor to be level. Before taking on the tasks of patching and leveling, the subfloor must be clean and free of loose debris. Some engineered wood flooring products are designed for glue-down applications when installing flooring over concrete slabs. Other products are better-suited for a nail-down installation where they are secured to a wood subfloor with nails or staples.

And for do-it-yourselfers, the preferred method is the floating floor installation which uses no glue or nails.

This article, however, focuses only on the glue-down application. Nail-down installations are covered in this article. Regardless of whether or not the flooring is glued, nailed, or floated, engineered wood flooring needs to be acclimated to its environment before installation — just like solid wood flooring. This can be done by periodically measuring the moisture content of the wood until it meets the guideline specs for installation. There are two types of wood moisture meters available; pin meters and pinless meters.

The latter being chosen more often for their non-destructive electromagnetic measurement capability. Another thing to check is the moisture levels within the concrete slab. Excessive moisture in a slab can damage an engineered wood floor and cause the plies to separate. Most flooring manufacturers require moisture tests for concrete moisture to validate their warranty requirements.

Scientific research from leading academic and industrial institutions confirms the reliability and accuracy of the ASTM F RH test at these depths. Slab preparation is critical for glue-down and includes sanding, scraping, leveling, and filling low spots because the slab must be flat so the planks can fit correctly. An adhesive is not intended to fill voids or deflections. Use elastomeric adhesives specially formulated for wood flooring so they conform to the natural characteristics of wood — expanding and contracting.

That is, their elasticity ensures that the engineered wood has an ample amount of space to expand and contract without causing the glue to break its bond. Be advised: using the wrong adhesive or applying incorrect amounts can lead to a failed flooring installation.

For example, use an adhesive that contains no water — like a moisture cure urethane or modified silane. These products are a good choice for these installations because they increase the strength of the bonding agent and offer a degree of structural flexibility.

A glue-down installation requires premium wood adhesives to be properly troweled over the concrete slab. Then the engineered wood planks can be laid into the adhesive and locked together at their tongue-and-groove joints. The adhesive manufacturer should have instructions regarding specific trowel requirements. Use a notched trowel to spread the adhesive.

NOTE: Wood adhesives recommended today are much more environmentally friendly than in the past, but they cost more. Installation Expansion gaps should be left between the flooring and wall. The manufacturer should have recommendations for how wide the expansion gaps need to be. Installing engineered hardwood flooring over concrete too tight against a stationary object will not allow room for normal expansion and may cause a failure.

Important: Only spread the adhesive over small areas ahead of you at any given time.