Moisture and Humidity Measurement Still Crucial for Engineered Flooring

Wood FloorWritten 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.

Seasonal Change Winter to SummerThe 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.

Natural and Engineered WoodAlso, 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.

Click here to learn more about orion moisture metersA good wood moisture meter is essential for any successful wood floor installation. Installers can easily use hand-held moisture meters to accurately and cost-effectively assess the MC of their wood.

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 used today as well as subfloors and wood materials. Wagner Meters’ Orion® wood moisture meters pinless technology offer fast and accurate readings of wood’s moisture content without leaving unsightly pin hole damage.

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.


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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.

Summary

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.

Last updated on May 4th, 2021

38 Comments

  1. gemma says:

    Hi,
    I’m installing a cork engineered floating flooring. ~2.5mm cork surface on a hdf core and 2mm cork under bottom. Installation manuals all recommend t-molding at all doorways and add 1/16″ to the already 3/8″ gap for over 30ft span. The manufacturer obviously has many warnings about adding gaps everywhere. Is there something about cork floor or using hdf that will expand in all directions that makes this floor different to other wood engineered floors? Does it expand more or less than other floors. I understand hard wood would expand in one direction along fiber, but hdf and cork is all directions.

    Also, when expanding more than 30ft is that in all directions, or just one way? like my room+hallway+room is just over 35ft long, but as most of it is hallway, and just expanding at ends, it’s not really a large area per say. Is it large expanses, or maybe more nooks, crannies, doorway pinching that are difficult for expanding/contracting floors?

    My installer doesn’t think t-molding at doorways is necessary, and I’m hoping for a slightly larger gap than 3/8″ where possible (the base boards are only 1/2″ so can’t be too much larger), but seems hard to cut to precision everywhere. When people talk about the gap do they expect it to be exact exact, or allow for human error and cutting so it’s not quite 3/8″?

    Thanks

    • Jason Wright says:

      Gemma,

      All floating floors expand and contract. Some require transitions in the doorways, some do not. Installers can maintain a proper gap along the edges without any trouble. Follow all manufacturers guidelines. Thanks for writing in.

  2. Andrew says:

    I have a house in Southern Spain and would like wooden flooring in the kitchen however my builder wont do the job because he said I would have problems with the humidity and yet I have seen many places in Spain with wooden floorboards. Am I missing something.

    Can you recommend a particular wooden floorboard that I could use?

  3. Gene Henry says:

    When I purchased my home in 2002 the foyer and dining room had hardwood flooring. This flooring was laid over a subfloor which was laid over concrete. The rest of the house had a thinner hardwood flooring over concrete. Hurricane Katrina did damage to the floor and we decided to replace the entire flooring with Bruce engineered flooring. The new floor in the foyer and dining room was laid over the original hardwood floor. Everything was great until this year when termite damage was found in the foyer under the new floor. A small part (approx. 5-6 s.f.) was removed and replaced as was the subfloor in this area. To do this the installer used treated wood to avoid any future termite damage. However, this area experienced some cupping some after installation. This was done about three months ago and the cupping has not fully resolved on its own. Also, the ends of the newly replaced pieces have a black stain at the end joints. Will the cupping fully resolve itself on its own and how can the stains be removed?

  4. Kevin Barbaro says:

    Hi! What should the relative humidity readings on engineered hardwood that has been down for about seven years be? Experiencing some cracking and the relative humidity of the wood is reading at 30%. Is that too high?

    • Jason Spangler says:

      Kevin:

      Thanks for the question. You are stating %RH IN the wood. I’m not sure how you are measuring that. Wood is usually measured in moisture content with a reliable wood meter. Most acclimated wood in a home would have a moisture content of 6-12% depending on the geographic location. Recommendations for interior temperature and relative humidity for the environment that have wood floors is typically 60-80F and 30-50% relative humidity. Hope this helps.

  5. Brandy says:

    Hi Larry,

    I had engineered bamboo placed in my home last March. I live in the mid-west and winter was still in full swing then. I’ve had to have 2 boards replaced within 2 months of install due to lifting/buckling. My flooring is now cracking throughout the house, discovered 7-8 months after install. Not actually sure when it actually began. The relative humidity in the home has been maintained between 40-60%. A flooring inspector hired by the bamboo company stated that the humidity in the floors was low throughout, with a reading exactly the same in every single spot tested in every room, including the small coat closet. What reasons could be to blame for low moisture readings in the floor with adequately maintained relative humidity? And should one expect to have the same exact reading in every single room on the first floor, including a small coat closet? Wondering if this could be a meter issue?
    Thanks!
    Brandy

  6. Tameka Wheeler says:

    Hi we have egineered floors in our home livingroom formal living and formal dining. Our floors bowed up in one area and the installers came to replace them. They ended up not replacing the floors because they said it was to much moisture in the concrete. We live in Texas. Our home is only one year old and we are having white clouded spots come up in a lot of areas on the floor. The floor has even split and cracked in one area. Our builders dont want to replace the flooring all over even when someone came out and said the floor is reading at 10 percent moisture in lots of areas. Will these floors last.

    • Jason Spangler says:

      Tameka:

      Thanks for the questions. Whether the floor will last is a very wide question that I can’t answer. It obviously doesn’t sound like it is going to perform the way it was intended. My biggest thing here is, if the floor was replaced once already and the contractor said it was because of excessive concrete moisture, then what did they do about the moisture to keep it from happening again when they installed the new floor? Good luck.

  7. Nancy says:

    Hi, we are considering either solid or engineered wood floors. There’s is so little that floor salesmen know or share with the consumer and what I have been told at times has been contradictory. We like in ky where many homes have solid hardwood. However salesmen talk about this area having too much humidity and how much better engineered wood is for this area. I believe this is a sales pitch. One question I have is 5” solid hardwood a lot more susceptible to cupping that 3 1/4? What about a 4”.
    We will be installing on main floor and we have a finished very insulated basement with a dehumidifier always in use. My husband is a hvac contractor and planning on installing a whole house humidifier. In our other home we had 60 yr old solid wood floors and never had problems with it. Also my other question is what’s is the main thing we should check for if we decide to do engineered wood instead?

    • Jason Spangler says:

      Nancy:

      Thanks for the questions. First off, I would recommend this resource https://www.woodfloors.org/ Yes they are pushing the virtues of wood, but the information they provide between engineered and solid is done in a way to educate so the end-user makes an informed decision. The wider the boards become the more critical moisture balance is, but in the narrow width range you are talking about I wouldn’t classify the difference “a lot”. I would make sure that you verify with the engineered and solid flooring manufacturers you are looking at that they recommend and warrant installations in a basement. In many cases, solid isn’t recommended here. Your last question about engineered/solid will be answered in looking at the link I provided above. Good luck.

  8. Mike Romain says:

    HI Larry, I live in Seattle and do have a furnace aircon system that removes small amounts of water, but not a true humidification control system. I am preparing to put in 7/16″ thick brazilian hickory (aka brazilian pecan) engineered flooring. I read that the ideal humidity range is 35-50% for installing this wood. Relative humidity outside in Seattle is higher than that.

    I’m going to purchase a hygrometer to know the conditions in my house. But would it generally be better to install the wood when RH is low inside the house (during the heating season), or higher (summer, maybe turning off the aircon for a few weeks to let humidity rise) or do i need to find a way to keep humidity in the suggested range? If so, only necessary during install or should I be looking into a humidification / dehumidification system, or am I overthinking this?

    The flooring seems to have two layers, a wood core (not plywood, but solid) with a 3mm wear layer of pecan wood. The existing floor is partly above a crawlspace with dirt and a vapor barrier with a 3/4″ plywood subfloor, with the majority being above a closed in basement with insulation in the basement joists and pecan will go directly over the existing 100 year old fir flooring (which shows some limited gapping but it is very old).

    Thanks in advance for any advice!
    Mike in Seattle

    • Larry Loffer says:

      Hi Mike,

      I am glad you are thinking about all the possibilities that could ruin a floor.

      It is essential to maintain constant humidity throughout the year.

      Wood is like a dense sponge, it will absorb moisture as well as release it depending on the surrounding conditions. If you install dry wood flooring in a high humidity environment, the flooring will gain moisture and expand (swell). The opposite will occur if the humidity is low, causing gaps between boards.

      What you need to do first is maintain the proper humidity level. Second, let the flooring equilibrate for at least 2 weeks where it will be installed. Third, it might be a good idea to check your subfloor with a moisture meter before installing the floor. Flooring installers should carry moisture meters. If you are installing yourself, I would recommend our Orion 910. Here is a link for more info about our moisture meters:

      https://www.wagnermeters.com/moisture-meters/

      Thank you!

  9. Zina says:

    Larry we have been having an issue with a Mohawk engineered floor. We have a slab home and a 10′ Kitchen island that opens to the LR area. on both the right and left side of the island we are experiencing a swelling area running diagonal across the floor. one side is 48″ long the other is 36″. One side the builder has pulled up planks and replaced. When the flooring was removed we found the the swelling run along the same direction as a crack in the slab. They put concrete sealer over the crack let it dry and then reinstalled the engineered planks. After about 3 weeks the area is swelling again.

    I do not see water pooling anywhere, the entire floor at the butt seems looks to me to be swelling, but the manufacturer says it is not. I think the problem is a combination of material and subfloor conditions. But moisture meter reading by installer shows within tolerance. Any way I could send ou some photos???

    Thank you

    • Larry Loffer says:

      Hi Zina,

      At this point, there are several factors that could cause this. There could be too much moisture in the concrete slab, the subfloor or the flooring itself.

      Did the Contractor use a moisture meter on the subfloor and flooring?
      The fact that the problem was around the kitchen island makes me suspicious of leaks.
      It is possible the concrete can absorb moisture, especially if there is no vapor barrier present.

      Another thought is… did the flooring installer let the flooring equilibrate to room conditions before installing?

  10. ron says:

    can the checks and cracks disappear in engineered wood flooring after it was installed over radiant heat and dry condition

    • Jason Spangler says:

      Ron:

      Thanks for the question. The cracks and checks may diminish, but they will never “heal”. It sounds like the heat and low humidity have caused the floor to shrink. Possibly adding moisture to the air, and in turn to the floor, some of these issues MAY become less noticeable. Good luck.

      Jason

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