Photo courtesy of Vexco


Having spent the last five plus years immersed in the subject of moisture problems in concrete and how to best control them, I have had the privilege of learning from and sharing information with the most esteemed experts on this subject in both the concrete and flooring industries. In recapping the information gleaned from the wealth of resources available, it became very clear to me that the picture of the problems and how best to solve them is blurred - fuzzy at best. Being the responsible party at Ardex and W.W. Henry to set the training agendas for our Sales Professionals, Distributor Partners, and Flooring and Concrete Installation Companies, the following is presented to sharpen the view on this whole “moisture in concrete thing” and to provide focus for you as you select a moisture remediation system.

One of the most important things you need to understand is that the problem we are looking at, representing billions of dollars per year in repairs, is due to moisture vapor: specifically from two sources – moisture vapor in the earth below our slabs and moisture from the “water of convenience” added to every concrete mix in order to place and finish it. The solutions offered to the industry by companies marketing moisture remediation products are not intended to address hydrostatic conditions, where liquid water is in contact with the bottom of the slab. Rather we are talking about moisture vapor moving up through the earth in an effort to “equilibrate” with the moisture conditions inside the occupied building, and we are talking about excess water wet put into the concrete mix as it is being placed. Given the above conditions, it holds that if we have a proper vapor retarder directly below the slab – AND – we allow our new concrete slab to dry (not “cure”) for a long enough period of time, a moisture remediation system is not necessary.

Photo courtesy of Ardex

The problem in our industry today is that while architects and design professionals are specifying proper vapor retarders directly under the slab in the new buildings being constructed today, the owners of these buildings would like them to be open and operating within a time frame that does not allow the concrete to evaporate the excess mix water such that the slab is dry enough to receive flooring. Add to this that we have countless renovation projects for slabs on and below grade where there may be no vapor retarder below the slab, or there was one once upon a time and it is no longer functioning as it should. Suffice it to say, regardless of whether it is new construction or existing renovation, there is a very high likelihood that some form of moisture control system is necessary prior to installing the floor covering. Here’s what you need to know about how these systems are supposed to work in order to make an informed decision as to how to correct a problem before it happens.

The most important step in determining a remediation course is to understand what it is you are trying to fix. Remediation of a moisture problem means that you have excessive vapor emissions coming from the concrete. Whether its new construction and not all of the moisture has dried out or it is a renovation project where there is no vapor retarder, what you are trying to do is to SLOW DOWN the emissions to a level that the flooring system can handle. If the manufacturer of the finished flooring says that their product (and adhesive, by the way) can handle a maximum of 3 lb. measured by the calcium chloride method, and the emissions from the slab equals 6 lb., we need to permanently reduce the emissions from that slab to a level that is less than 3lb. – lets say 2 for the purposes of this example – in order for the flooring to perform.

Another way of looking at this is to make an analogy with someone we can all readily grasp. Let’s say there is a 6-lane highway heading out of town. Cars are zipping along at a good clip, only to encounter an immediate change to three lanes as soon as you hit the next town. No warning signs, no speed bumps, nothing. Six lanes of traffic turn into three lanes in an instant.

But what if we were to install two tollbooths just as you enter the next town? We would put up some warning signs and maybe rumble strips and we would all be fumbling in our pockets for a few coins or bills to pay the toll. We would also have the opportunity to slow down and jockey for position in one of the two lines since we know the only way through is via the tollbooths. We get in line, pay our toll and emerge from the booth with three lanes of traffic to choose from. Take your pick and go.

That’s all we’re trying to do with a moisture control system: take 6 lb of moisture emissions and slow it down to 2lb. so that when it reaches the flooring system that can handle 3 lb., we’re home free. In case you didn’t notice, the “toll” you paid is just the cost of the moisture control system selected.

So, understanding what it is that a moisture control system has to do, let’s take a look at some of the key performance characteristics we should look at when selecting the right system for our project.

Photo courtesy of Ardex

#1 - Pay attention to what the moisture control system says about how much moisture the system can handle after installation. Various manufacturers will say that their system works up to “X” pounds of moisture. This consideration may have credence when dealing with a new construction project that has a vapor retarder below it and all we are worried about is the water of convenience leaving the slab. The problem is that the emissions from the surface are not always a good indicator of the available moisture present – hence the relative humidity testing we are learning about. Add to this that the slab may not even have a vapor retarder below it and the 8 lb. we are trying to control becomes too large to handle.

What we have learned is that, since the surface of the concrete is invariably drier than it is 4 or 6 inches down, once a floor covering is applied, the amount of moisture at the surface of the concrete will increase. So what may have been 8 pounds at the time of the test will climb to 10 – 12 – 14 or more. How many of you have had flooring installed when it was below 3 lb only to turn into a moisture-related failure some 6 months later? Now it is easy to understand why. Its not so much what the level of emissions from the surface of the concrete are now, it is what the selected moisture control system can handle after it is installed – that’s what really counts!

Photo courtesy of Ardex

#2 - Make certain that when selecting a remediation system, the one to be used will perform in an environment with high pH. Often overlooked is the mechanism of a flooring failure due to increased pH at the flooring adhesive/concrete interface. The flooring start to bubble or blister, we remove the flooring and the adhesive is all slimy and gooey and looks as though it was just spread this morning. Truth is that it was installed 6 months ago. We see an adhesive mess and assume that it got soft and loosened up by the moisture emissions when the fact is that the emissions caused an increase in the pH of the concrete up to a level of 11 or 12 and it is this high pH and not the moisture directly, that caused the adhesive to break down. Don’t forget that along with the maximum allowable moisture emissions from the concrete, most manufacturers put a maximum pH (9 is the most common) on the concrete as well.

The same mechanism that causes the moisture emissions to become elevated over time when the moisture within the concrete migrates toward the surface is the same reason the pH rises as well. What may have been a benign 9 or 10 pH on the surface of the relatively “dry” concrete can increase to 12 – 13 as the moisture emissions rise. This high pH creates an environment that destabilizes certain kinds of adhesives, particularly those we use to adhere flooring with high vinyl content, and we have very expensive flooring failures. Lesson learned – if we know the pH of the concrete can rise with an increase in vapor emissions, make sure that your remediation systems can handle very high pH conditions.


#3 – Select a system that can be easily applied completely and uniformly over the entire area and to the specified thickness. All this really means is that make sure that you are putting enough material on the concrete so that the product can lower the permeability of the concrete to a uniformly accepted level. Laboratory tests are great and they allow us to make informed decisions about products based upon side-by-side comparisons. However, when it comes to actually working on the job, the product applied to the concrete has to work just as well as in the lab test over every square foot of that floor.

In most cases, some type of mechanical preparation is required on the concrete surface (ICRI CSP#3 is most commonly quoted) prior to installing the remediation system. The manufacturer of the system will require that the material be applied to a uniformly specified thickness to achieve the laboratory measured perm rating. Since the most commonly used remediation systems are in liquid form and are hand applied on site, how easy is it to coat the slab to obtain the minimum mil thickness that will reduce the vapor emissions uniformly over the entire floor.

Some products being sold to reduce moisture emissions are recommended for coating at a rate of 400 sq. ft. per gallon. An acrylic emulsion system with 50% solids will dry to a mil film thickness of 2 mils. I don’t know about you, but no matter how hard I try, I can’t even paint my living room walls in one coat at 400 sq. ft. per gallon and achieve full and uniform coverage. And that’s over a very smooth surface. It is even more difficult to obtain proper minimum coverage over a concrete slab that has been shot blasted. Make sure the system you are installing is capable of performing over the entire floor area.

Photo courtesy of Vexco

#4 – If you don’t have a moisture emission problem, one coat of virtually any system will work fine! The tone taken here may sound ridiculous if not downright pompous at first, but having heard enough of the horror stories about failed systems, the experts have convinced me that two coats are essential to the overall performance of the moisture control system for a couple of reasons. The first is reflected in #3 above - two coats of paint on my living room walls are a sure bet that I’ll get the coverage I’ll need for a uniform appearance. Two coats of a remediation system on my slightly roughened concrete give me a much higher comfort level that I’ll have sufficient product to slow down the moisture emissions to an acceptable level.

The second reason, and the one that makes item #4 not so ridiculous or pompous, is that some manufacturers tell you to install their product in just one coat, but then require you to test the surface of the concrete after coating to make sure the emissions have been reduced properly. On many occasions it has happened that one coat turns into 3 or 4 (or more so I‘ve heard) coats to get to an acceptable emission level. Not only do you run into additional costs for material and labor, every time you have to retest the emission levels using the calcium chloride method, it adds three more days to the process. Then you find out there is still too high a level of emissions, and you’ll need a second coat, and another retest, and in some cases a third coat? Realistically, all things being equal, think about this: with all of the information presented, it is only logical that if one coat of a waterborne product is applied at 4 mils wet to a concrete slab and the flooring performs properly, it means that you didn’t have excessive moisture emissions in the first place.


#5 – How well can the remediation system stand up to traffic from other trades after it is installed? While this may not appear to be a critical item when making the initial assessment for the flooring to be installed, this is a performance issue that cannot be overlooked. If a remediation system is put down and the floor covering is placed right away with no other trades or traffic of any kind in between, there is only the flooring contractor to blame if the system is in any way compromised. Having said that, we have all been involved in enough actual jobsite situations to know that in spite of our best efforts to plan ahead, the flooring may not be installed immediately and other trades need to proceed to do their work as well. While this isn’t the fault of the manufacturer or installer necessarily, traffic can damage the installed system making it incapable of performing. For this reason, consideration must be given to the construction schedule and the system’s ability to remain intact should it need to be trafficked over by other trades until the finish flooring is installed.

Over the longer haul, what’s to say that the owner of the space decides to change the flooring in five or six years? Tear out the old and install the new. Will this process compromise the integrity of the moisture remediation system? If removal of the flooring violates the remediation system, the system must be re-installed to ensure protection of the new flooring. The owner paid for this five years ago; does it have to be budgeted again?

Photo courtesy of Vexco

#6 – Does the system selected allow the floor covering contractor to install the floor using materials and techniques that are usual and ordinary? If the installer needs to change his usual flooring installation procedures, make certain that the new instructions are clearly understood and can easily be followed. For example, on commercial projects, the most common substrate over which flooring is installed is porous concrete. But by installing a moisture control system over the concrete you end up with a nonporous surface. That same adhesive the flooring mechanic uses day in and day out may not be the right adhesive to use over a non-porous substrate. And even if it is the same, the installation instructions have to be carefully understood.

Since waterborne adhesives are the most common in use today, their installation instructions are directly tied to the porosity of the substrate to include the size of the notches in the trowel, and allowing longer open times before actually placing the flooring into the adhesive. While these installation instructions are readily available from the adhesive manufacturers, it remains that the contractor using them has to be aware of them and understand that the type of adhesive, the size of the trowel notching, and the open time of the adhesive may be different now that the remediation system has been installed over the concrete.

Photo courtesy of Vexco

# 7 – Check the warranty being offered very carefully and make sure that the installation is fully covered and for the full term of the warranty period.

If there is a failure and the moisture level does not exceed what the manufacturer recommended for the system installed, what is actually covered? In some cases, the manufacturer will replace the product only. Does additional warranty coverage come with additional costs? Who gets the warranty? Can the owner pass it on should they sell the building? What is the length of the warranty? Is it prorated? What is really covered: tear-out; reinstalling a new system; patching or leveling as required, the adhesive, the floor covering, labor?

The installation of a properly formulated moisture control system should flat out perform for the full length of the warranty period. Owners expect warranties that will protect them from future outlays. They’ve already spent good money to solve a problem. They should only have to pay for it once.