Moisture and Humidity Measurement Still Crucial for Engineered Flooring
Written by Wagner Meters, published first by ProInstaller (Summer 2014 issue). Nearly 75 years ago, Swedish wood flooring company Kahrs introduced engineered wood flooring. As an alternative to hardwood floors, engineered wood flooring is comprised of a relatively thin layer of hardwood glued to a core of plywood or some type of fiberboard that’s not visible.
In recent years, engineered flooring has surged in popularity, both in homes and commercial applications, for several reasons. It comes in a wide variety of colors, textures, and strip widths to suit most any taste, it is durable and cheaper substitute for solid wood floors, and it is more versatile and eco-friendly.
Because engineered flooring is less prone to moisture damage, it can be installed over a variety of surfaces in many applications, including basements, kitchens, and bathrooms with light moisture.
Although an engineered floor can, in many situations, be a better choice than a solid wood floor, it is not perfect. For instance, complications may occur after installation due to undesirable moisture and relative humidity (RH) levels in both the engineered product and the concrete sub-floor.
In addition, despite the fact that engineered flooring can be installed in places unsuitable for solid wood, it is not meant for extreme conditions. Installers should be aware that large humidity swings, excess moisture, and lack of climate control can cause engineered floors to break down just like wood floors.
Relative Humidity Concerns
The space for the engineered flooring needs to be conditioned based on the manufacturer’s guidelines. Manufacturers typically require a range between 35% and 55% ambient RH, but those guidelines can vary. Some manufacturers may have a range of 40-60% RH while others may require 30-50% RH.
It’s important for installers to know if the end-user has the ability to control the climate within those ranges after installation. Otherwise, trouble can occur.
For instance, if an engineered flooring manufacturer’s low RH range is 40% and the product is installed in Nevada where the average RH is about 30%, problems can occur – unless the end-user is able to control the RH.
The same issue can occur in the Midwest where the humidity varies widely between winter and summer. When it’s 5° F outside, it’s difficult to maintain the RH at 40% when the furnace is running constantly. Such imbalances can lead to checking/splitting, delamination, and end-gapping. In these cases, flooring failures may not be covered under warranty.
Variances in RH can occur from floor to floor or even room to room. For instance, humidity levels can rise in a building because of humidifiers, steam radiators, moisture-generating appliances such as dryers, or combustion appliances such as stoves. Cooking and showering also can increase indoor humidity.
When indoor RH is low, “dry cupping” can occur in engineered flooring. The top wear layer tends to dry out much faster than the core board material, especially if the wear layer is thin. As the wear layer rapidly dries, it tends to pull away from the bottom core material. The result is a cupped floor, with the corners lifting or curling first.
In addition, splits and checks can also occur when RH is low. Splits are openings that run from top to bottom, while checks are smaller openings that don’t run as deep. The stress in the boards can also cause the finish to show wrinkles or ruptures.
To prevent complications because of low RH, it’s recommended that the end-user install a whole-house humidification system that turns on with the heat. Whole-house humidification systems not dependent on heat also are available for arid climates such as in the Southwest. At the minimum, small portable humidifiers can also be used. The key is to keep the RH levels constant, even if a bit high or low, to prevent cracking and checking in the boards.
Wood Moisture Concerns
Although engineered wood flooring is less prone to moisture damage, it is wood after all and still requires the same MC management as any other wood product. All wood holds moisture content. As the RH rises, wood absorbs moisture from the air. And, as RH falls, wood releases moisture into the air. Wood, therefore, must be allowed to reach its equilibrium moisture content (EMC). That is, it must reach a balance between the wood’s MC and that of the ambient conditions.
Also, some engineered products combine several woods, each with its own distinct MC characteristics. If installers don’t pay sufficient attention to those wood characteristics, problems may follow.
Another important factor about engineered flooring is that the core and the wear layer react differently to moisture. If the two have different MC levels, they can become out of balance. The performance of the floor in these conditions depends on several factors, including MC at the time of manufacture, core construction types, and thickness of the wear layer.
For instance, it’s often claimed that “the thicker the wear layer, the better the flooring”. That claim may not always be true. Moisture may affect a thicker wear layer in a manner similar to solid wood – in effect, expanding and contracting more than a thinner wear layer.
If the top wear layer and the core have the same shrinking tendencies, engineered wood will move just like solid wood. If the top layer and the core shrink differently, then the panel is more moisture sensitive. This can cause more shrinking and warping.
As a general rule, the core of engineered flooring is more dimensionally stable than solid wood flooring because of its multiple layers of plywood, high-density fiberboard, or hardwood. However, large humidity swings, excess moisture, and lack of climate control will cause an engineered floor to fail just like a solid wood floor.
Experts in the wood flooring industry recommend measuring for MC and RH before and during installation. Relying on old-fashioned methods of feeling the wood or eyeballing the sub-floor can be risky, resulting in costly problems later.
Wagner Meters offers a complete line of wood moisture meter products designed to meet almost any use, and they can measure the MC of the majority of wood flooring species used today. Their proprietary pinless technology offers fast and accurate readings of the wood’s MC without leaving unsightly pin hole damage. For instance, Wagner Meters’ MMC220 Extended Range digital wood moisture meter reads MC between 5-30% up to a three-quarter-inch depth.
It’s important to take moisture measurements at the time of delivery, before acclimation, after acclimation, and after job completion. Waiting until the floor shows defects from shrinking and cupping may be too late to file a claim since the MC at the time of delivery cannot be determined.
Concrete Moisture and RH Concerns
Although engineered flooring can be installed successfully on either on-grade or above-ground concrete slabs, it’s critical to understand that moisture measurement and management are necessary for the concrete slab as well as the hardwood flooring. Like wood, concrete has independent, changeable moisture levels that vary with changes in ambient RH.
Concrete absorbs water vapor as RH rises and releases water vapor into the air as RH falls. Moisture can also enter concrete from other sources, such as excessive rainfall, ground seepage, or a leaking appliance. This will upset the balance between ambient conditions and the conditions necessary to have engineered floors look and function properly. The reverse is also true. Installers, therefore, must be certain MC levels are stable in both concrete and wood before combining them.
According to flooring industry standards, concrete sub-floors should be given enough time to dry to an appropriate RH level before engineered flooring is installed. In this instance, installers should use a wood moisture meter to ensure precise moisture measurement of the finished wood flooring product and an appropriate RH testing device to ensure concrete feasibility for installation. Wagner Meters has the equipment to perform both types of testing. Assessing the concrete and wood moisture levels separately reduces the potential risk of future moisture related problems that can occur when combining the two materials.
Certainly, engineered flooring provides customers and installers with a number of options for an aesthetically-pleasing, long-lasting installation. However, it’s important to know the conditions where the flooring will be installed and the acceptable RH range from the manufacturer. While engineered flooring may be less susceptible to moisture, the flooring material, and the concrete slab should still be checked for moisture to avoid costly call backs and unhappy customers.
Larry Loffer is a senior technician at Wagner Meters, where he has over 30 years of experience in wood moisture measurement. With a degree in Computer Systems, Larry is involved in both hardware and software development of wood moisture measurement solutions.