A close look at adhesives: Wood Cuts

By Brett Miller

By most accounts, adhesives were first used as an installation method in the wood flooring industry more than 50 years ago. Back then, options were limited, but ingenuity was not. In fact, those pioneer installers borrowed technology from their brothers in construction, specifically, their roofing counterparts.

For years, roofers had used asphalt to adhere shingles to roof tops, and it seemed just a leap of faith that the same method would work for wood floors. It was simply a matter of spreading the molten asphalt onto the prepared subfloor and then embedding the wood flooring into the asphalt before it sets. The work was difficult, messy and dangerous, but from these auspicious beginnings the adhesive wood flooring installation method was established.

Things have changed a bit since then. Today’s advanced technologies make adhesives an ideal installation method for most types of wood flooring. Determining when and how to use adhesives properly is the difference between a quality installation that will last for years to come and one that will cause headaches down the road.

The adhesive installation technique is used most often with engineered wood flooring products but can be used with some solid wood flooring products too, if it is recommended by the manufacturer. Adhesives work well over a wood subfloor, as well as over a concrete subfloor, making them ideal for basement, condominium and slab construction installations.

There are several types of wood flooring adhesives available on the market today. They include water-based, solvent-based and moisture-curing urethanes. Each type has pros and cons, and installers will need to do their research to find the product that will best fit their installation needs and also meet flooring manufacturer requirements. Do they want to work with an adhesive that is easy to use? Do they want an adhesive that will deliver long-term performance? Are they willing to deal with regulations that impact how they conduct their installation? All of these considerations will have an impact upon which product they ultimately choose for their installation.

Generally, water-based adhesives are easy to use but may not offer the same performance as other adhesives. This type of adhesive can also have an adverse effect on the wood. Solvent-based adhesives are moderately easy to use and have good strength. This type of adhesive, however, is regulated, and installers will need to adhere to strict rules and regulations concerning its use. Moisture-curing urethanes also are moderately easy to use, provide the strongest bond of the three types of adhesives mentioned, and will last for the life of the floor. This type of adhesive is regulated as well.

Over the years, adhesive technology has advanced to the point that the benefits are fairly universal no matter which type is used. Today’s wood flooring adhesives are very strong, very elastic and, once they are cured, very permanent. Innovations, therefore, currently focus on additional features that make the products more user-friendly, like ease of use, allowable subfloor moisture control, one-step systems, ease of cleaning and green benefits.

Traditionally, if a contractor wanted to use a moisture control system with an adhesive, they would likely be using a two-step system. This means that they first would need to apply a moisture retarder or moisture barrier to the subfloor and allow it to dry completely, then come back to apply the adhesive necessary to install the flooring material. Today, many manufacturers are offering one-step systems that combine the moisture and adhesive steps. This saves the contractor significant time on the jobsite, since an entire step, including time lost for drying, is eliminated. Current systems are marketed as 2-in-1, which combines an adhesive with moisture protection; 3-in-1, which combines an adhesive with moisture protection and sound control; and 4-in-1, which combines an adhesive with moisture protection, sound control and crack isolation/bridging.

Another major advancement in the wood flooring adhesive industry is the move toward the promotion of green, environmentally friendly products through the use of modified silanes. Silanes, which also are called silicon tetrahydrides, are inorganic compounds that are a colorless, flammable gas with a sharp smell used in the production of adhesives. Modified silanes, which also are called hybrid adhesives, address two issues. First, they promote a more environmentally friendly adhesive by using silane technology as opposed to isocyanates, which are organic compounds used in polyurethane production that can have negative health impacts.. Second, they have an easier application process and are simpler to clean.

Progress has also been made in the production of reduced volatile organic compound (VOC) products. VOCs are organic chemicals that have a high vapor pressure at ordinary room temperature. Their high vapor pressure results from a low boiling point, which causes a large number or molecules to evaporate from the liquid or solid form of the compound and enter the surrounding atmosphere.

VOCs are numerous, varied and ubiquitous. They include both manmade and naturally occurring chemical compounds. Some VOCs are dangerous to human health and can cause harm to the environment. Anthropogenic VOCs, which are VOCs that are caused or produced by humans, are regulated by law, especially indoors, where concentrations are the highest. Harmful VOCs typically are not acutely toxic, but have compounding long-term health effects.

VOCs in wood flooring adhesives are solvents and are commonly used to make adhesives less viscous. In recent years, legislation regarding allowable VOC levels has changed dramatically. Laws vary by region, and it is important for contractors to know the laws for the areas in which they are working. In California, the California Air Resources Board (CARB) monitors air quality for the state of California, but in other areas of the U.S., such as the Northeast, regulations are governed by the Ozone Transport Commission (OTC).

There are adhesive products available today that are marketed as having zero VOCs, but the VOC limits for wood flooring adhesives currently is 100 grams per liter, or 0.8 pounds per gallon (per the South Coast Air Quality Management District Rule #1168). The rule applies to all commercial and industrial sales and applications of adhesives, adhesive bonding primers, adhesive primers, sealants, sealant primers and any other primers.

The responsibility for compliance generally lands in the lap of the manufacturer of the product. They are required by law to manufacture their products to meet regulations and must clearly label their products to include required compliance information on the container. It is important to note, however, that while the bulk of the responsibility falls upon the manufacturer, ignorance of the regulations will not excuse a contractor from fines and repercussions, which can be severe.

No matter which product is used, all wood flooring adhesives require the same degree of jobsite preparation to ensure a successful installation. In fact, thorough jobsite preparation is crucial in the long-term performance of the floor and becomes even more critical if the installation will occur over concrete.

Contractors should make sure that the wood they use is properly acclimated to the jobsite. This step simply cannot be rushed, as it is a recipe for disaster. While this takes place, contractors should turn their attention to the subfloor. First, contractors will need to make sure that the subfloor is flat. In general, industry standards define this as a 3/16” variance over a 10’ area. If low areas are encountered, contractors will need to use a floor leveling compound, which cures quickly. If high areas are encountered, they will need to be ground down. In addition, the subfloor should be cleaned thoroughly by removing all dust, debris, paint, oil, stain, drywall mud or any other foreign material that could negatively impact the bonding characteristics of the adhesive. Moisture levels in the subfloor, the wood flooring material and the atmosphere must be measured, and must be within the NWFA Guidelines or the recommendations of the flooring manufacturer before the installation can begin. Finally, contractors should not be tempted to use concrete sealers, as these can have a negative impact on the installation down the road.

After the jobsite is ready, and the installation process is ready to begin, contractors should be sure that they use the adhesive recommended by the flooring manufacturer. Adhesive directions should be read carefully and only the trowel recommended by the adhesive manufacturer should be used. Contractors also should pay close attention to the flash time and the open time of the product. They should not exceed either one during the installation process. Once the installation is completed, the floor should remain untouched for at least 24 hours to allow the adhesive to properly cure. The reduction of foot traffic during this process will greatly improve the long-term bonding of the adhesive.

It is unlikely that the wood flooring contractors who first experimented with adhesive installations a half century ago realized the impact their innovation would have on wood flooring, but today adhesive installations represent a large part of the industry. The FlooReport by Market Insights LLC states that of the 1,062 million square feet of hardwood sold in 2013, 55% was engineered wood flooring, and by all accounts, the majority of that wood was installed using adhesives. Needless to say, this is an industry trend that is expected to “stick around” for years to come.