Dewpoint is the temperature at which the humidity in the air begins to condense in and on the concrete substrate. Floor coverings and adhesives should not be installed any time the air temperature or concrete surface temperature is within 5ºF above dewpoint. Photo courtesy of Parterre.

Dewpoint problems are often mistaken for moisture problems. Consider a flooring installation that has been tested for moisture via the calcium chloride or relative humidity test method along with a pH test. The installer has taken great pains to ensure that the project goes error-free.

Less than a month later, blisters begin to appear beneath the flooring material, and/or there is adhesive wheel tracking in the material or oozing at the tile joints. Upon further review by opening up the flooring material the adhesive is wet, gummy and stringy. The adhesive has not cured (re-emulsified).

Next, a series of events start to take place establishing the guilt or failure of the flooring, the adhesive or the installer. The manufacturer is brought in to establish whether the material and/or the adhesive are defective, and the litigation cycle (i.e. expense, downtime, lost revenue, damage to customer goodwill and reputation, etc.) begins.

The effects of dewpoint are nearly indistinguishable from those associated with a classic moisture problem. In reality, dewpoint is a transitory effect that can be easily controlled at the time of installation – if the installer is made aware of its existence and how to control potential detrimental effects. Let’s examine the causes and effects of dewpoint and ways to avoid the problems associated with it.

What is dewpoint? Dewpoint, as it pertains to concrete and other substrates, refers to a confluence of environmental conditions (temperature and humidity) to create a “wet” substrate – even when there is no direct exposure to a water source! Water droplets or condensation on a cold glass of liquid are examples of dewpoint’s effects. This is a critical point to remember in any floor installation.

When dewpoint occurs in concrete, the resulting moisture migrates to a cooler, damper environment. So, if the concrete surface and/or interior area are cooler than the room temperature, the moisture will migrate towards that area; the volume of moisture migration is regulated by the available amount of moisture in the environment (i.e. in highly humid air, or from the water in water-based adhesives). The porosity and permeability of concrete surface dictate the efficiency of the moisture movement. This is among the reasons why good concrete mix design and finishing are so important.

How can this create problems during and after the installation? The problem occurs when a water-based adhesive is installed over an already damp substrate (even when the concrete surface appears to be dry). If the room environment is humid, it is difficult – if not impossible – for an adhesive to properly set. So, even if the adhesive appears well transferred to the floor and the concrete, the moisture content of the concrete surface may be too high to allow the adhesive to properly cure – provided it cures at all.

Basically, in the presence of sufficient moisture, the adhesive acts as if it is still in the container. Because moisture in liquid form is quite cohesive, it tends to move towards pockets of void space (larger and small) and manifests itself as blisters in sheet vinyl. In vinyl composition tile (VCT), the adhesive complicates matters when foot and rolling traffic causes it to ooze out through the tile joints. Because it tends to equalize with the environment, the moisture can wick toward the seam or joint area, which in turn retards a complete set of the deposited adhesive. As attempts are made to remove unsightly adhesive residue, the still-liquefied adhesive beneath the VCT moves to the just treated area -- closing the circle on a vicious cycle.

This is but one reason why it is vital for any testing entity to be well-schooled and certified as competent in moisture testing protocol and interpretations of its results. Without knowledge and consideration of dewpoint and its effects, the testing entity runs a distinct danger of creating a totally avoidable problem. Errant testing and evaluation can lead to spending time, resources and money on an unnecessary and usually expensive moisture-control system. As a point of conjecture, imagine how frequently a successful installation of a moisture control product had been used on a project where the problem was actually misdiagnosed.

The best way to avoid dewpoint problems is to become aware of your immediate surroundings and the environment in which the flooring materials will be installed. The surest way of determining your environment is to conduct measurements of the room and concrete surface temperatures, the relative humidity and dewpoint.

This is a lot easier than it sounds, thanks to improved and affordable testing apparatus. The equipment I consider vital to measuring job site conditions:

Hygrometer: Measures humidity (as opposed to a hydrometer that measures specific gravity).

Thermometer: One used for measuring ambient air temperature and another – which is more difficult to find – for measuring concrete surface temperature

Dewpoint meter: There is a combination hygrometer/thermometer/dewpoint measuring meter that does all three functions.

During the installation, the relative humidity within the jobsite should be less than 60%. It may be necessary to set up air movement devices, like fans or blowers or dehumidifiers, to precondition the room and maintain a proper environment throughout the installation process.

Why have dewpoint problems become so common? Three key factors have contributed to an increase in dewpoint related problems: use of water-based adhesives, changes in construction requirements and fast-track building processes. Let’s look at each of these in greater detail.

Water-based adhesives. As more water is added to adhesive formulations, the more critical a dewpoint condition can become. Water-based adhesives tend to cure slower than their solvent-based counterparts, leaving them more susceptible to moisture related problems. Further complicating this equation are the film of the adhesive (trowel notch) and open time (the time allowed for an adhesive to develop before the placement of the material into it).

It is important to note that when most of the so-called modern moisture-sensitive adhesives have completely cured they are at least as durable in high-moisture conditions as traditional solvent-based products.

Changes in construction requirements. Unmodified older buildings have a natural air exchange, anywhere from one to four exchanges per hour. This, in turn, may help control moisture-related problems by diluting and dispersing any moisture within the building. The tighter the building’s envelope, the lower the infiltration rate and natural circulation of the air. In traditional historical restoration, the steps to correction of moisture problems have been to seal the building so completely that the building cannot breath.

Fast-track building practices. Time is money. As a result, more structures are being built faster, with little or no regard for the natural curing and/or seasoning of the building materials. Concrete cures very slowly and, for several months after it is poured, contributes to overall moisture problems as water evaporates from its pores. Due to their moisture content, drywall, drywall texturing, plaster and paint can contribute to interior moisture problems as well.

Also, artificial heat sources are often overlooked contributors to interior moisture content. One commonly used fuel – propane – has high water content, approximately 90% by volume (this is why it is referred to as a hydrocarbon). The two most common by products of propane are water and carbon dioxide. If you have ever visited a jobsite where propane is being used, you’ve probably seen the windows sweat (a manifestation of dewpoint).

If concrete is cold, a common situation during the winter months, the moisture will move to the cooler, damper side of the slab (bottom). As a result, the concrete doesn’t dry out completely. The carbon dioxide and moisture associated with propane heating conspire to increase the propensity for immediate and future moisture problems.

Dewpoint is an important consideration and, in our analysis, it constitutes at least 30-40% of the moisture problems we encounter. Considering the high percentage of misdiagnosed dewpoint conditions, it is no wonder that many conventional moisture control efforts have demonstrated apparent success.

Our industry needs to be properly informed about dewpoint and other moisture-related conditions. Increased knowledge will help us quit wasting money, time and resources on misdiagnosed problems and, ultimately, allow us to allocate our time and resources wisely.