Sub-floor prep for glue down installation

Because of its stability and compatibility to various installation methods, Engineered hardwood flooring has become very popular in many markets.  Although it can be glued, nailed/stabled and floated, more and more contractors will recommend the glue down method even over plywood sub-floor.  This is largely in response to the prevalence of OSB plywood sub-floor.   OSB plywood doesn’t hold clits or stables well, therefore the engineered wood planks can come loose over time.  In this post, I will like to address a few key points while preparing the concrete and plywood sub-floor for glue-down installation.

Many flooring adhesive manufacturers offer guidelines in sub-floor preparation.  Not only it is crucial for the installer to follow the guideline to ensure proper adhesion, it also ensures full manufacture warranty is honored.  In general, the concrete slab should be free of glue residue from carpet, loose debris or any major cracks.  Then the leveling should be checked and kept within the tolerated range of the flooring to be installed.  Light sanding is also recommended to “rough-up” the surface for better bondage between the glue and wood planks.  Unfortunately concrete sanding is often omitted by contractors to save time.  Most consumers are not aware the importance of concrete sanding and how it can affect the outcome of the installation.

Sanding off glue residue from old sheet vinyl flooring.









The same procedures should apply to OSB sub-floor as well.  The plywood should be free of all glue residue.  Nails used during construction should be checked and hammered.  If the installer noticed any loose or squeaky areas in the the plywood, fasteners should applied to secure the plywood.  Sanding is also recommended to increase adhesion of the glue.  Often contractors will start to apply flooring adhesive as soon as the carpet is removed.  This could also cause the glue to fail or left many hallow spots under the flooring.

OSB plywood after sanding. Clean and free all any glue residue.












Sub-floor preparation is the first step of flooring installation.  It is the foundation of a successful installation.  However, once the flooring is laid, it is very difficult to verify if the preparation is done correctly.  And since the effect of a carelessly prep sub-floor could take years to show, if at all, it is often forgotten in the installation procedures.  So when discussing the flooring project with your installer please make sure you are clear with what to expect from the work.  Also verify with the glue or flooring manufacturer’s guidelines and make sure correct steps are taken during preparation for the warranty to be full honored.

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