Understanding Concrete Moisture - October 2011

By Jessica Chevalier


In the U.S. market, insurance claims related to concrete moisture totaled $1 billion in 2009. This number represents not only significant cost and waste (in ruined floorcovering) but a threat to the health of the commercial floorcovering industry.

Chris Hand of Allegheny Contract Flooring in Winchester, Massachusetts reports that large retailers like Walmart, Whole Foods and BJ’s Wholesale Club are bypassing the possibility of a concrete moisture problem (and the cost that comes with it) by choosing a polished concrete floor, which breathes and therefore doesn’t trap moisture, instead of one with a floorcovering. This is not good news for the floorcovering industry because it represents hundreds of thousands of square feet of lost sales in every location, and it makes it imperative that the industry find a way to fix concrete moisture issues, regain the trust of these major retailers and win back this business. 

Problems with concrete moisture occur when floorcovering is installed atop a concrete slab that is not fully dried or when an existing slab is exposed to a new source of moisture. When this happens, adhesives can fail, flooring can buckle or bow, and molds that adversely affect indoor air quality can grow between the slab and the floorcovering. 

According to Lee Eliseian, founder and president of Independent Floor Testing and Inspection (IFTI), concrete moisture problems aren’t knowledge problems but behavior problems. Eliseian explains, “The industry knows what’s good for it, but it keeps up the same bad habits.”

Most all of these bad habits are related to fast-track building. Owners want buildings completed as quickly as possible so that they can collect rent or get their own cash registers ringing with sales (an understandable goal in this economy), and that leads to as-quick-as-possible building and, for the concrete slab, less drying time. In fact, industry experts estimate that construction schedules have been compressed by 30% in the last decade. “It used to take a year to build a grocery store,” says Eliseian. “Now it takes four or five months. But concrete doesn’t care what our schedule is.”

In addition to that, since the installation of floorcovering is one of the last steps in the construction process, time and money are both especially short at that juncture, which means that building owners and contractors are more willing to cross their fingers, cover the slab and hope for the best. Fortunately, challenges with concrete moisture are both preventable and fixable if all parties involved in construction (from building owners to the subcontractors who pour the concrete) are willing to slow down and follow specific procedures.

Of course, there are a hundred small decisions that rush a project along and lead to a final problematic result. Most significantly, architects and owners often fail to lay out their requirements for concrete testing in the construction documents (testing by a third party firm should be the rule, according to Eliseian) and also don’t outline a path of action (or set aside funds) for handling a concrete moisture problem if it does occur. These are the large, conceptual means of eliminating concrete moisture problems but coping with the physical implications of a concrete moisture problem is another challenge.

Concrete is a porous material that acts like a sponge when exposed to liquid, wicking moisture to its surface. Concrete is made of cement aggregate, chemical admixtures and materials like fly ash and slag cement; water is added to this mixture to create a chemical reaction that, after drying, results in a product that is essentially man-made rock. While it only takes a 0.25:1 to 0.28:1 water to concrete ratio to hydrate concrete, more water is added (raising the total amount to between 0.42:1 and 0.5:1) so that the material is workable and can be poured; the “excess” water (everything over 0.25:1) is called the water of convenience. In order for a slab to be dry, all water of convenience must evaporate. If the water to cement ratio is 0.4:1, it takes about 46 days for the slab to dry. If it’s 0.5:1, it takes about 82 days. But the drying process cannot even start until conditions are right: a slab in a humid environment will not even begin the drying process.

Different concrete purveyors have different mixes for their concrete (and different mixes are created for different uses), but, for the most part, these mixtures are fairly standardized. In other words, unless a concrete purveyor deviates from the standard, problems with concrete moisture aren’t generally due to the way that concrete is initially mixed. However, the origin of problems may begin shortly after the concrete leaves the mixing site. 

On commercial building projects, it is common for many concrete trucks to sit in a line, waiting to pour their loads. The danger with this process is that the concrete trucks at the rear of the line risk having their load harden while they wait. As a result, truck drivers often add water to their mix as they wait to ensure that the concrete remains pourable.

Why is this a problem? If a driver has added water to his concrete mix, all drying time estimates are out the window, and some spots in the concrete will be much wetter than others. In general, one truck pours about 1,000 square feet of concrete. If, at the point of testing the concrete’s moisture level, a tester does not follow ASTM standards (which dictate that three tests should be made for the first 1,000 square feet and one test should be made for every additional 1,000 square feet), a wet spot may be missed, and that spot may develop a moisture problem. 

There is another danger during the pour that leads to concrete moisture problems. Vapor barriers are placed beneath all pours to protect the slab from moisture. However, the barriers can be punctured during the pour, allowing moisture a point of entry. Since the subcontractors who are in charge of the pour don’t generally have a personal or financial stake in the project, they are sometimes not as careful as they should be about avoiding this. Of course, once there are several tons of concrete atop the barrier, there is no way to repair it. 

In addition, over time, barriers degrade, so an older building may develop a moisture problem—even if it has never before had one—due to barrier decay. 

A concrete moisture problem may also develop after the slab has initially dried, if the landscape around the building changes, funneling water towards a grade-level slab, or if the water table rises. 

Most of the experts that we talked to believe that concrete moisture problems are unwavering but not increasing. Though fast track building is surely the biggest culprit, contributing factors are to blame as well. 

Barrett Morton of Shaw Commercial believes that location is often a problematic element. “During the past ten to 20 years, growth has necessitated that new builds be placed in less desirable physical locations. These areas may present unique challenges due to the physical attributes of the locations.” As buildings are increasingly built on slopes or in low-lying areas, for example to accommodate an expanding population, the concrete slabs under these homes may be more at risk of contact with water. This may contribute to a steady trickle of concrete moisture problem cases.

Some within the industry blame the proliferation of concrete moisture problems on the industry’s preference for water-based, rather than solvent-based, adhesives. Many believe that these new, greener water-based adhesives are more susceptible to water than previous adhesives, but other industry experts dispute that fact. 

Unfortunately, when adhesive breakdowns do occur, they often don’t occur right away. According to Paul C. White of Paul G. White Interior Solutions, a commercial and residential floor contracting firm in Maine, “Adhesives can take months or years to break down and fail if proper testing and mitigation have not happened.” White notes that the salts brought to the surface of the concrete in the vapor contribute to adhesive breakdown.

Says Terry Fitzpatrick, national installation services manager for Mannington Mills, “The flooring industry has introduced moisture resistant adhesives that are more tolerant of water of convenience, but these don’t remediate a bad slab.” 

Chris Hand is one expert who does believe that the greening of adhesives (through the removal of solvents and asbestos) has contributed to installation failures related to moisture, but he notes that no one in the industry is suggesting that those ingredients should be reintroduced because “no one wants to take responsibility if someone gets sick. No one wants to accept liability.” 

Hand doesn’t believe that moisture problems are increasing, but he notes that, “There is a lot more awareness about moisture in concrete now than there was five years ago. People are more aware because they have seen installation failures.”

Eliseian started IFTI in 1997 after spending 15 years as owner of a floor contracting firm. His firm was contacted regarding a slab moisture problem at a retail drug store that had resulted in several floorcovering failures. Eliseian and his company researched concrete moisture mitigation systems, applied a system and solved the problem. Soon, Eliseian realized that addressing concrete moisture issues was a great strategy for setting his firm apart from other flooring contractors. 

In 2004, Eliseian sold his flooring contracting business to focus on IFTI, which now has a dozen employees in its California office and over 200 IFTI Certified Field Technicians across North America. About 95% of IFTI’s business is on the preventive side of the business. “Unfortunately, many customers have had to go through the pain of a concrete moisture problem to adopt a preventative mindset,” he says. 

Eliseian’s firm conducts a battery of tests (all of which are standardized through ASTM) to determine the conditions of a concrete slab. It does not rely on a single test, and it conducts all tests to ASTM standards. 

The first step to successful concrete moisture testing is to establish good data regarding the conditions of the space. Testing should only be done when a building is fully enclosed with the HVAC units operational. If the building is not fully closed, testing can produce results that are inaccurate—results that, unfortunately, often indicate that it is okay to move ahead with floorcovering installation. Testing under the right conditions is a major hurdle for experts, who are often called in too soon and expected to come to a definitive conclusion on whether the floorcovering contractors can move ahead.

Moisture content in concrete flooring is expressed as the number of pounds of water being emitted per 1,000 square feet in a 24 hour period. It used to be common that floorcovering adhesives could not endure more than three pounds of moisture. Some of today’s adhesives can tolerate as many as eight pounds of moisture. 

Acceptable moisture levels also vary based on what floorcovering is specified. Several of today’s more popular commercial floorcoverings are contributors to concrete moisture problems because of their dense, impermeable constructions. Fiberglass-backed sheet vinyl is much less permeable than the felt-based vinyl, and modular carpet tile is denser (and therefore less permeable) than broadloom. “The denser the construction, the more it is affected by moisture,” says Ray Thompson, owner of the Floor Covering Institute. “Epoxy terrazzo is worst, and broadloom is best.” Because of this, it is especially important that flooring contractors abide by each product’s specifications for installation. 


The Plastic Sheet Method: An 18:x18" sheet of clear plastic is secured to the concrete surface with tape on all four sides. If, after 16 hours, the plastic has condensation on it, the concrete is still wet. However, a negative result (no condensation) does not necessarily mean that the concrete is dry below the surface. The plastic sheet method is considered inaccurate if the plastic is placed in direct sunlight or if the space is excessively hot. Ultimately, though the test is simple, inexpensive and non-destructive, it does not provide quantitative results.

Relative Humidity Test: This method measures the humidity under a sealed chamber on the surface of the concrete. After the chamber has been sealed for 16 to 24 hours, a capacitance based humidity gauge is used to make a reading. This low-cost and non-destructive method produces quantitative results.

Relative Humidity Probe (RH Testing): This test involves measuring the relative humidity of the concrete at a specific depth from the surface. A hole is drilled then allowed to sit for 72 hours to achieve moisture equilibrium. The method is useful because it can measure the dryness of the slab at different depths and can monitor the progression of the drying over time. Many of the experts that we consulted cited RH testing as their preferred method.

Calcium Chloride Test: In this method, a dish of calcium chloride is weighed, then placed in a sealed chamber on the concrete's surface for 72 hours. After that time has passed, the calcium chloride is removed, weighed again and the difference between the original weight and the second weight is calculated. This inexpensive and non-destructive test produces quantitative results; however, the test is not favored by industry experts because it is sensitive to the atmospheric conditions of the space, and it only provides a snapshot of what is happening in the top 1/2" of the concrete.

Gel Bridge Test: Concrete conducts electricity and conductivity is increased in the presence of moisture. In the gel bridge test, a hole is drilled into the concrete, then filled with a conductive gel. Two metal pins, attached to a measuring instrument, are placed in the holes and the conductivity of the concrete is measured, then judged against the conductivity of dry concrete. The gel bridge test is complicated by the inconsistent nature of concrete as a medium (variations in the aggregate used, voids and concrete mix ratios), so results aren't always accurate.

Radio Frequency Test: Since water molecules absorb radio waves, radio frequency instruments are used to read how a wave transmits through concrete. As with the gel bridge test, the aggregate type, concrete mix and voids will impact the readings. While some radio frequency machinery does account for different aggregate sizes and types, it does not consider voids or variations in the concrete mix.

According to Fitzpatrick, “Resolution [of a concrete moisture problem] is always ugly. By the time a moisture issue rears its head, often six months to a year after the pour, the buildings are often occupied.” The majority of concrete moisture problems occur on large pours like schools, hospitals and large retail locations. Once tenants are in the space, the problem becomes more than the cost of replacement materials, remediation materials and labor. The costs of lost business hours, moving expenses and lost rent are significant and often unquantifiable, not to mention the toll a situation such as this takes on tenant-landlord relationships and among co-workers within an organization.

When a problem does occur, Morton reports that the first call is typically made to the flooring contractor to ensure that they performed their duties properly. Did they understand the issues presented by the site? Were the proper moisture tests performed? 

Eliseian believes that the contractor cannot be held responsible if he wasn’t given the tools and time needed to get the job done properly—in other words, if he was just following the specifications laid out for him. 

But Hand sees it differently, “As an installer, if we install over a substrate, then we accept the conditions. When we install, we are accepting responsibility for whatever we’re installing over.”

If a building owner does not want to spend the time or money to properly handle a moisture problem, the contractor may request a release, which will exempt him from liability for problems relating to the slab conditions. This is fairly common practice, according to Eliseian.

If the problem cannot be rectified at the contractor’s end, the floorcovering manufacturer is sometimes called in to evaluate the problem, but if the manufacturer has clearly laid out the product’s requirements relating to moisture tolerance, and the product has performed, they can’t be held responsible.

Since the concrete supplier generally follows fairly typical procedures, as was discussed earlier, they aren’t usually at fault either, which leaves the architectural firm, who is writing the specifications on behalf of the owner. Eliseian says, “There is a loose consensus in the industry that the architects and owners are responsible because it is their design. If the owner wants the project completed in months, that’s what has to happen.”

The options for fixing a moist slab are fairly direct. Giving a concrete slab time to dry is the easiest solution to eliminating concrete moisture problems, but it is not always the most practical solution. Since a slab cannot begin to dry until conditions are right, the process doesn’t begin until doors and windows are installed. Once these elements are in place, the key is to get air moving quickly and constantly, until the slab has naturally dried. Because this is simply not feasible time-wise in many situations, other options are utilized.

An alternative path, according to Morton, is using a sand blaster to make the floor porous and breathable, then applying a topical epoxy seal to the floor. The seal will create a barrier, so that water cannot escape through the surface of the slab. This is an effective and long-term solution. However, it’s also an expensive one. Epoxy barrier systems typically cost between $3.00 and $4.00 per square foot. For an average size Walmart Supercenter (185,000 square feet) that adds over $700,000 of cost.

Penetrant fluids applied to a concrete slab are designed to penetrate the surface and react chemically with the concrete, with the goal of reducing the moisture vapor emission rate. While these penetrants are cheaper than epoxies, they are also less effective.

Desiccant drying is another option for remediating a moisture problem. In desiccant drying, the air in a space is circulated through absorbent materials—similar to that little packet of beads you find in a box of new shoes—thereby eliminating moisture from the space. However, the process is expensive and, if done too early, can cause the slab to crack and curl. Dehumidifiers are sometimes used as well to increase the vapor emission out of concrete, but results are very slow.

There are a few companies marketing admixtures (additives mixed into the concrete pre-pour) as moisture solutions. When sodium silicates are added to wet concrete, they interact with calcium hydroxide and make a gel, which is supposed to block moisture in a slab. Hand reports that, in his experience, these admixtures haven’t produced convincing results, nor do they have a long track record of success. As companies work to further develop these innovations, they may become a solution in the future, Hand believes. 

Dr. Heather Brown, director and associate professor of concrete industry management at Middle Tennessee State University, says that she has had some success with using admixtures to effectively improve moisture vapor transmission in her lab. However, she stresses that lab results are not necessarily consistent with job site results, since job sites present a plethora of variables. 

However, Brown believes that the skepticism about admixtures arises from a variety of factors. First of all, many admixtures are difficult to enter into the mixture. Second, the span of pricing for these admixtures is broad. “The price range is dramatic, so I think contractors begin to doubt the inexpensive products and don’t want to pay for the expensive options. The range of pricing can be $0.30 a square foot to over $1.00 a square foot. With so many options, it is difficult to wade through the products to find the ones that are proven performers.” 

The real goal, of course, is to avoid getting to the point of needing physical intervention. To that end, Eliseian advises that building owners include specific language in the construction specifications regarding what they expect in terms of testing. In addition, third party testers should be brought in to conduct concrete moisture tests on all pours; a path of action should be outlined in case of adverse test results; and money should be set aside to fund a mitigation process.

What third party practitioners does Eliseian recommend? “There are many solo practitioners who are very competent, but they are localized, so they don’t have the reputation of an organization backing them.”

He warns against organizations that do a broad range of construction site testing. These organizations often get commissioned to do the testing simply because they are already on site performing soil tests and the like, but concrete moisture testing is generally just a side business for them, not an area of expertise.

IFTI has a moisture testing technician certification program that trains people to “do it right,” notes Eliseian. “People often ask me why I’m training my competition. I tell them that training people to perform testing correctly and creating competition isn’t our challenge. It’s the ignorance of the need for testing that’s our challenge.”

Much to the relief of many a building owner, Eliseian reports, rarely is a slab replaced. “In most situations, a moisture problem can be corrected, and a floor can be installed.” 

Copyright 2011 Floor Focus