The old school method was to use hard board, staple, patch and sand it, then install whatever the resilient product was. Well, the evolution has caught up. Underlayments are just not that generic anymore. It seems the resilient manufacturers have stepped back from underlayment and placed the decision on product usage upon whomever is supplying and installing it. There is a large choice of products, and the range is ever increasing with imported woods. In fact, it is easier for the flooring manufacturer to provide information on what not to use. Then again, those recommendations will vary.
There are conflicting installation recommendations between the manufacturers on issues such as whether to: butt the panels, or leave a slight gap; patch the joints, or don't; sand before patching the joints, or sand after patching the joints. While some panels are pre-printed with a stapling grid, other manufacturers recommend a random stapling that does not leave a pattern that could telegraph through. The objective is the same for everyone: provide a clean, smooth surface that an adhesive can bond to.
Common sense, quality materials and good work practices are the path to follow. Selecting a quality underlayment is not too difficult a challenge. Never use a panel that is not specifically recommended for use as an underlayment. The APA, American Plywood Association, has a grading system that serves as a reference. Your supply distributor is another resource that can assist and provide the installation recommendations that match the exact flooring product. The very last thing any installation contractor wants to hear is that a resilient installation replacement is due to their underlayment problem.
Consider these factors when selecting an underlayment product:
• The panel is specified for the application.
• The manufacturer provides a written warranty.
• The product has written installation procedures.
• The product meets the requirements of the resilient and adhesive manufacturers.
Common failure related points:
Discoloration - Sources of staining or bleed through are from printing, marking, paints or stains, oil, and grease on the panel or the substrate. Inappropriate fasteners can also be a cause.
Staples - Stapling is the most common fastening method used. Problems associated are that the staples are too shallow, leaving a bump, or are too deep, causing the staple to pull through. The length of the staple should be sufficient to penetrate firmly into the substrate, but not through it.
Loose spots - These are areas that generally were overlooked and received no staples, the tool ran out of staples, or the staple was too long thereby penetrating the substrate and working loose.
Floor patch - Weak products can break down and crumble or support growth of mold that can stain the surface.
Sanding - Lack of consistent sanding creates humps, especially when panel joints have been patched.
Existing substrate - Underlayment contours the existing substrate, so it is sometimes necessary to fill low spots or sand high spots prior to installing the panels.
Lay out - Improper offsetting of panel joints or alignment of panel joints with substrate joints.
Trimming - Failure to leave an adequate expansion gap around wall areas may cause the panels to buckle.