Sticking Around Through The Years

Wood flooring contractors who experimented with the application of adhesive some 50 years ago had little idea about the huge impact they have created today. With advancement in technology, adhesive has become an indispensable element of wood flooring. By Michael Martin, National Wood Flooring Association


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 simply was a matter of spreading the molten asphalt onto the prepared subfloor, and then embedding the wood flooring into the asphalt before it set. 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 will be 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 as well 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, condo, 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. 

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 lack long-term performance and strength characteristics. This type of adhesive can also have an 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 in the US. 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 in the US 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. These features include things 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, he or she 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. After it was dry, the contractor would then need to 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 into one process. 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.


Go Green

Another major advancement in the wood flooring adhesive industry is the move towards 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 colourless, 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 hazardous organic compounds used in the production of polyurethanes. Second, they have an easier application process and are easier to clean.

Like silanes, modified silane technology is based on reactive polymer chains that join together to form a meshed network. With modified silanes, however, the isocyanates do not function as the reactive chain-linking moiety (a part or functional group of a molecule); the silane serves this function. This is beneficial because silanes are silicone hydrides. Silicone is an inert compound, meaning it has little or no ability to react, and it is non-toxic. Silane technology, therefore, promotes a greener solution to isocyanates, which have been postulated to cause some adverse health reactions in humans.


Control The VOC Level

Another green advancement for wood flooring adhesives is the production of reduced volatile organic compound (VOC) products. VOCs are organic chemicals that have a high vapour pressure at ordinary room temperature. Their high vapour 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 in the US, 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 in the US 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 US, such as the North East, regulations are governed by the Ozone Transport Commission (OTC). Generally speaking, these organisations have implemented regulations to reduce the overall VOC emissions from products in an effort to reduce both environmental impact and human exposure. Products imported into the United States must comply with these regulations as well.

There are adhesive products available today that are marketed as having 0 VOCs, but the VOC limits for wood flooring adhesives currently is 100 g/L, or 0.8 lb/gal per the South Coast Air Quality Management District (SCAQMD) Rule #1168. 

This Rule is intended to reduce emission of VOCs and to eliminate emissions of chloroform, ethylene dichloride, methylene chloride, perchloroethylene, and trichloroethylene from the application of adhesives, adhesive bonding primers, adhesive primers, sealants, sealant primers, and any other primers. The rule applies to all commercial and industrial sales and applications of adhesives, adhesive bonding primers, adhesive primers, sealants, sealant primers, or any other primers. 

The responsibility for compliance generally lands in the lap of the manufacturer of the product, whether the product is made in the United States or in another country exporting to the US. 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.


Preparation & Installation

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 will 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. To properly prepare the subfloor, contractors will first need to make sure that the subfloor is flat. In general, industry standards define this as a 3/16-inch variance over a 10-foot area. 

If low areas are encountered, a floor levelling compound will need to be used, which cures quickly. If high areas are encountered, they will need to be grinded 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 national 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 realised the impact their innovation would have on wood flooring, but today, adhesive installations represent a large part of the industry. 

According to a report published by Catalina Research, among the 1,148.5 million square feet of hardwood sold in the US in 2013, 57.1 percent was engineered wood flooring, and by all accounts, the majority of that wood was installed using adhesives. In fact, in some areas of the US, coastal areas in particular, it is estimated that up to 75 percent of all wood flooring installations use adhesives. Needless to say, this is an industry trend that is expected to ‘stick around’ for years to come.

Rate this item
(0 votes)

FDMAsia About Us

For almost 30 years, FDM Asia has been the publication of choice for woodworking professionals in Asia Pacific, providing the latest news and expert insights of a diverse range of topics including process technologies, furniture production, panels manufacturing, raw materials handling and sustainability issues.

We have one of the most comprehensive woodworking database and e-media programme to assist you in your e-marketing and give you an exclusive opportunity to connect to our 25,152 online subscribers.