Flooring underlayments for laminate, hardwood and resilient flooring are designed for many things—including sound absorption, stability, moisture protection and extra comfort underfoot. Whether recycled rubber, cork, wood composite, foam or sheet, these products are built to withstand everyday stresses…as long as they’re installed properly.

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Subfloor prep

“Subfloor prep is critical to any successful installation for any underlayment and the major source of failures. Inadequate prep results in laitance [an accumulation of fine particles on the surface of concrete] and other bond-breakers, forming a barrier between the underlayment and the subfloor,” said Joe Hostler, Dependable general manager. “In laymen’s terms, if you don’t clean up the dirt, you are going to stick to it instead of the concrete underneath.”

According to Larry Scott, DriTac vice president, field technical services, subfloor preparation is key for all types of floor coverings. “Proper subfloor conditions center primarily on being clean, flat and dry as commonly referenced by industry-accepted standards. Proper subfloor preparation is paramount and should be among the preeminent objectives when attempting to achieve a successful flooring installation.”

David Ford, vice president of sales and marketing, Stauf USA, echoed those sentiments. “Subfloor prep is the foundation of good installation. If you have hollow spots or high spots in the floor it could turn a great floor into a less than appealing installation.”

Patrick Giles, vice president, technical and R&D, Maxxon, also stressed the importance of subfloor prep. “Components of floor prep are moisture or relative humidity testing, and determining floor smoothness, flatness or levelness as well as whether floor patch and sanding will be necessary. Also important is determining the porosity of the subfloor, whether a primer/sealer is required and choosing the proper adhesive depending on your findings.”

Bas Vangenderen, managing director, InstaFloor NA, said even small imperfections in an improperly prepped subfloor can spell trouble. “These small imperfections can cause echo chambers to form below the hardwood unless the underlay adheres to the base of the board. Non-adhesive underlays with irregular subfloors fall away from the base of the board in the subfloor depression areas and footstep noise is reflected back into the room.”

Moisture concerns

Determining the amount of moisture in a subfloor is critical. Improper installation can lead to many problems in the substrate and in the flooring, such as cracking, creaking and unwanted panel shifting.

Moisture testing is an essential part of prep, noted Brad Miller, vice president of product management and development, QEP. “A moisture test is always recommended on the subfloor before installing any type of flooring. Flooring should never be installed over subfloors with a moisture level that exceeds the recommended level as stated by the flooring manufacturer.”

Testing the moisture levels can never be skipped when installing hardwood flooring, Ford explained. “Moisture vapor testing is an absolute must. The slab has to be tested for vapor emission—no slacking in this area. It’s as important as using a trowel for spreading. Don’t assume a slab is dry just because it looks dry.”

Hostler stated that the nature of hardwood flooring to expand and contract in all directions makes moisture control underneath hardwood critical. “For slab installations, we recommend contractors follow ASTM 3010. This requires a perm rating of .10 or less which will ensure that the hardwood can handle the moisture emissions coming from the subfloor.”

When in doubt, consult the manufacturer. “Subfloor moisture control requirements are typically determined by manufacturer recommendations and subsequent moisture testing conducted prior to the floor covering installation,” said Scott. “There are several types of moisture mitigation products available on the market. Make sure to first check the manufacturer specifications before installing any kind of floor type, and that includes underlayments.”

Vangenderen noted that a vapor retardant or Damp Proof Membrane (DPM) is required below hardwood floors where there is any concern regarding moisture. “When in doubt use a DPM. This does not have to be part of the underlay, but could be a separate 6 or 12 mil polyethylene sheet or Visqueen. The underlay can then be laid on top of the DPM and the hardwood installed on the underlay. This is a highly effective moisture barrier system that is simple and cost-effective to install.”

Sound control

“Acoustic performance of a flooring system greatly improves the perception of quality and comfort of occupants and neighbors,” stated Eric Kurtz, hardwood installation systems market manager, Bostik. “While acoustic underlayments are available for use under floated floors to reduce sound transmission between floors, the sound of footsteps on the floating flooring is typically much louder than footsteps on glue-down flooring applications.”

Jack Boesch, MP Global Products director of marketing, said sound control underlayment is most often installed in multi-family properties. “If you’re in a single family home you’re not as worried about the transfer of sound.”

In sound control situations, wood underlayments are typically floated over or glued to the top floor, noted Dale Asp, national business development manager, Impacta. “Rarely will it be acceptable to nail. There are underlayment options that offer a sleeper system that will allow you to nail 3/4” solids without compromising installation. It is important to note that by using this method you won’t penetrate the actual acoustical product; therefore you won’t compromise the acoustic value.”

He added, “There are some acoustical underlayments offered on the market that are designed to both correct subfloor imperfections as well as offer sound control. Like anything else, any imperfections being dealt with must be within reason for these solutions to be applicable.”

Giles prefers a specific sound control product installation when working with LVT. “LVT applied directly over a sound mat is temporary sound control if the underlayment itself is not floating over a sound mat. If you remove and replace it with a different floor finish, the sound control may change for the worse. LVT installed directly over sound mats have trouble at the lower end of the frequency spectrum, which can generate footfall complaints.”

He added, “It is my opinion and significant experience that permanent sound mats be installed under a pumpable underlayment, which, with the appropriate mat, would meet or exceed footfall code before the finished floor coverings, as this allows floor finishes to be changed and replaced over the years without sacrificing sound control.”

Other considerations

Operations manager of Builders Granite & Tile in Houston, Andres Lopez, says an essential part of the installation process is getting it right the first time. “We as installers have to be cautious. We have to make sure we’re using proper adhesives so the flooring is able to function properly. The only downside I see with LVT is when it comes to the repairs—planking tends to suffer a bit more through the construction process.”

Resilient flooring is also susceptible to telegraphing, said Bob Cummings, Pak-Lite sales and marketing manager. “Telegraphing is where objects below the floor visually show through to the top of the vinyl flooring over time. Its cause can be traced to cracks and minor protrusions in the subfloor or variations in height of the subfloor.”

Vangenderen noted floor prep for resilient is much more demanding because of this reason. “Resilient floorcoverings tend to telegraph any subfloor imperfections, which become visible and unsightly when looking down at the floor. Laminate and hardwood are more forgiving of minor subfloor imperfections, but major subfloor problems will still need to be addressed and rectified before installation.”

Miller emphasized the importance of choosing the right underlayment for the job. “Picking the right underlayment for your flooring and the type of installation is essential to the success of the project. Good surface preparation and the right underlayment mean beautiful floors can be enjoyed for many years. The underlayment is just as essential as the flooring itself.”