Site Preparation For Glue-Down Wood Floors

How to Install Engineered Hardwood Flooring:

This section, is designed to answer the following:
  • How to prepare your room for flooring installation?
  • What is required as a subfloor?
  • Can it be installed over radiant heat?
  • Does it matter what width of flooring I buy?
  • Are there special issues associated with a new house?

For nail-down, click HERE for instructions installing a classic 3/4″ solid wood floor. These instructions are not meant to replace a professional installer, but rather to help our customers understand the process and help those that wish to install the flooring themselves, with some introductory information.

Please read carefully all the information included with your flooring purchase, and follow the manufacturers recommendations as your first line of defence!

What subfloor is considered adequate for Engineered Floors?

Plywood: As with standard 3/4″ nail down flooring, The National Hardwood Flooring Association recommends a minimum of 5/8″ tongue and groove plywood as a base. Aspenite or any other particle board product is not considered to be suitable substitute.

If you are very fanatical you may choose to add a layer of 1/4″ plywood on top to cross laminate over the seems. In installations where the edges of the original subfloor are seen to bridge at the seams, the extra layer of 1/4″ ply helps to even out the hills and valleys that can show through the relatively malleable 3/8″ flooring.

Concrete: Many of these products can and are designed to be glued down to a concrete base. Check with the individual manufacture for guidance, and follow specific instructions for moisture barriers etc.

Mirage recommends a number of glue manufacturers that WILL warranty an engineered wood floor, glued to a concrete slab, as long as there are NOT any related moisture problems in the concrete.

Testing your subfloor before installing MIRAGE engineered floors?

  • subfloors must be tested to see how level they are. Your floor must be flat to within 3/16″ in 10 feet. Sand high spots with a floor sander, and fill low spots with an appropriate floor leveler (make sure it is given time to properly dry).
  • All old flooring must be removed, if it does not provide a solid gluing surface (or a new subfloor installed over top)
  • the prepared surface must be clean for good glue adhesion.

Wood Subfloors: It is essential that a wood subfloor be screwed down every 6″ to the underlying floor joists. Once that has been completed, although it may seem kind of stupid, it is a good idea to jump around on every corner of the floor, to locate any remaining squeaks.

Add additional screws and reblock the floor from underneath in those areas that persist in squeaking. Don’t let anyone convince you that squeaking can be solved by nailing or gluing a new floor on top. At that point, it is usually too late to solve the problem!

Concrete Floors: A concrete floor must be free of grease, oil or dust. If it has been coated or painted, and you wish to glue your flooring directly onto the concrete, you may have to wash it with an acid to etch the concrete, prior to installation. This will improve the quality of adhesion, between the concrete, glue and floor.

Ask your installer for advice!

All cement floors must be properly dried (typically 60 to 90 days old for new concrete) before considering any floor installation.

Test concrete slabs for moisture!

Tape a 15″ square of clear polyethylene plastic to the concrete slap with moisture resistance tape, sealing the plastic around all four sides. Leave it for 24-48 hours. If no condensation collects under the film, then the slab is probably dry enough to install your floor. Test a number of different locations around the room and test it in the damp part of the year.

Use heat and fans to speed drying if necessary, on a new slab. If this is an older home and moisture problems are present, DO NOT install wood flooring. The glue will not hold in most cases and the moisture will get into the wood and cause all kinds of problems

Below Grade vs At Grade Concrete Slabs

When a cement slab is located at ground level (at grade), you don’t usually run into problems with moisture, once the slab has cured properly, and can easily glue this type of wood flooring directly onto the concrete. BUT, with the traditional basement floor, that is lower than the surrounding land (below grade), drainage around the house becomes a key issue in determining whether you will have moisture issues.

A “wet basement” can exist one time of the year and not another, or “one year” and not the next….. so be sure that you are comfortable in saying you DON’T have moisture problems year round before you invest any dollars in any kind of wood floor.

Plywood laid over concrete on below grade applications:

If you wish to install a subfloor, over a concrete base, for insulation or to address minor moisture issues, please see these web sites from Industry Associations:

Can I install an Mirage engineered flooring over radiant heat?

Yes, its construction with a plywood base and a layer of solid wood, laminated on the surface makes the product more dimensionally stable (relative to a solid wood floor). It can withstand minor fluctuations in temperature, caused by an infloor heating system. It is a great choice!


  • Narrower plank flooring will always be more stable then its wider cousin, thus avoid wider planks when possible.
  • Make sure your radiant heat system has been operating for a number of days prior to installing your floor, so any residual moisture is removed.
  • check the moisture as suggested above.

The fact that it can be glued down, gives one a degree of comfort in not worrying about putting a nail through one of your pipes during installation….. but yet still ending up with a floor that looks exactly like a traditional 3/4″ solid wood floor.

There are many different methods of installing radiant heat systems, both for new homes and to retrofit an older home. This is beyond the scope of this article, but let me say this:

  • Most important is to have a system that works on water volume and low temperature (most new systems).
  • Low operating temperatures, go a long ways not to shock your floor and cause any buckling or cupping.
  • Systems with external thermometers help to maintain a steady even water temperature with limited radical movement,even though the external temperature may fluctuate. Look for this feature.
  • For more information try: The Hardwood Council Tips on Installing Hardwood Flooring over Radiant Heat

Installing wood in a new home, are there special considerations?

Follow the advice for a traditional wood floor, get your house to a reasonable humidity (ie under 55%). Although Mirage engineered floor is more dimensionally stable, it is still made from natural wood fibres and will react to excessively high or low moisture levels.

New homes, at the initial construction phase tend to have high moisture content from drying concrete foundations and new paint. Buy a hygrometer and for a few bucks monitor the moisture and protect your flooring investment.

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