Moisture Testing for Concrete Floors- What Measures What? Part 2

Now that we've dispensed of the fallacy of water vapor as a cause of flooring and coating failures, it's time to establish the difficulties of correctly measuring for moisture content of the concrete surface.

Moisture Migration - It is primarily Top-Down not down-up

In earlier articles, I have covered the misinterpretation of data that has led to more moisture claims than ever before, simply because the "facts" of moisture testing do not match what we are taught.

The causes have ranged from vapor pressure to hydrostatic pressure and high humidity, with THE method that will solve all our problems...only these facts haven't solved anything, only made them worse since none of these "causes" was ever a concern to begin with.

The situations again begin with the chemical complexities of concrete and the misinterpretation of data.

The Two Factors of Concrete Quality - Water to Cement Ratio and Curing

It has long been surmised that a low water content is capable of producing quality concrete. Coupled with proper curing practices, the end product should last for decades or even longer. Yet with all of the grandiose declarations, even concrete designated as HPC (High Performance Concrete) has under-performed badly.

Even as lab study after lab study continues to tell us these SHOULD be performing better than what is being delivered, again there is this obstinate refusal to accept that repeating the same things over and over and expecting a different result isn't working, won't work and never will work when the changes and history are taken into account, the current standards remain in place.

Low water to cement ratio and optimized curing is desired, but the challenges presented in the field are not allowing either method to function as intended and as "proven" in the laboratory. Since the field results fall well short of laboratory results, it's time to dig in and explore why this chasm exists.

The 28 Day Curse

Irrespective of where in the world the studies are conducted, the stated goal is to achieve a specific compressive strength at 28 days. Occasionally a study will extend the timing out to 56 days, but any conclusions tend to become muddled since any issues are dealt with on a speculative basis rather than taking a deeper dive, particularly when it comes to what the chemistry IN the concrete is doing and why it is doing something that is constantly left to speculation or simply not being addressed.

It has been very well established through historical data and MANY studies that concrete exposed to elevated temperatures will tend to have higher 28 day strengths, which everyone cheers, yet the higher the temperatures, the lower the 365 day strength is, no one says a thing, since it is now someone else's problem. Therein lies the crux of the situation, as long as we continue with the emphasis ONLY on getting the construction schedule on time, the outfall creates a situation where project after project becomes someone else's problem, which end up becoming an economic drain on everyone. Back in the 1980's, Time and NewsWeek Magazines sounded the alarm on our failing infrastructure. 40 some years later, our infrastructure has only gotten worse, even after spending billions each year to try and catch up on defective and deficient structures and roads.

The concrete industry has established the 28 day benchmark which initially was a benefit, but now has become an albatross. Curing with water and then with curing compounds was an effort to ensure the concrete developed its full potential.

The curing process back when cement was a coarser grind and there was more cement in a given strength design, the curing process was VERY successful. In a 1984 article by Ev Munro for Concrete International magazine. It was noted that the more rapid strength development of the finer grind led to a lowered cement content to achieve the same 28 day strength target. In the UK, modern concrete in the 1980's were using upwards of 34% less cement to achieve the same 28 day strength. The internal heat generation prompted more stringent curing requirements since the finer cement grind also produced increased heat of hydration. Also not considered was the permeability of the modern concrete was much higher, upwards of 500% more permeable than its earlier predecessor. What was NOT considered was this more modern concrete might be less durable.

Moisture Testing History

Basically the first standard method of testing was to tape down a sheet of plastic, let it sit overnight and check to see if there was any moisture present when the plastic was peeled back.

Another method briefly used was to pour salt onto the surface to see if the salt would dissolve. Table salt was used, until someone found that calcium chloride could reveal moisture levels where the table salt wouldn't. NOTE: This is an area where people should understand the critical humidity threshold of salts. The critical humidity threshold of table salt is 74-76% RH. The critical humidity threshold of calcium chloride is approximately 28-30% RH. This means the humidity levels, once exceeding 30% will cause the calcium chloride to dissolve and become liquified. The table salt (sodium chloride) wouldn't liquify until the humidity levels exceeded 75%. NOTE: This is a chemical form of "dew point" (ionic dew point) where condensation will occur at humidity levels well below that of atmospheric dew point.

This apparently made it way into being covered with a lid of some sort which eventually morphed into the calcium chloride method. The details of what and why the 3 and 5 lb moisture limits are convoluted, with competing theories as to who and why these levels were developed.

Flooring manufacturers who began seeing an uptick in moisture claims, particularly in the era where solvents were increasingly removed from usage and the industry was desperate for something "scientific sounding" they could latch onto. Making things even worse, the "cause" of moisture failures was caused by "hydrostatic pressure", another scientific sounding label many, if not most flooring and coating manufacturers latched onto as the moisture problems increased.

It was about this time where I began to become involved with moisture-related flooring failures after spending my prior years in waterproofing and restoration, particularly with historical and underground structures. I vigorously objected to the term hydrostatic pressure (since hydrostatic pressure with grade level concrete is a violation of the laws of physics) with any grade level concrete and became aware that virtually NONE of the flooring or adhesive manufacturers understood even the basics of moisture-related failures.

Not letting the concrete industry off the hook, I took issue with many of the published experts in the concrete industry who stated vapor pressure was the cause of epoxy and cementitious coating delamination. This was a low-level of sophistication that competed with the hydrostatic pressure supporters. NOTE: in any livable environment, vapor pressures cannot exceed 0.5 psi. then consider an epoxy has an adhesion exceeding 100 psi, it wasn't difficult to figure out vapor pressure was a non-issue.

Calcium Chloride gives way to RH probes

Calcium chloride was a standard and remains so for many flooring and coating manufacturers. As it became increasingly clear that calcium chloride tests were not an optimal solution, other methods attempted to come forward to take the helm. I will say that the majority of calcium chloride tests are conducted incorrectly with essentially no oversight on if and when these incorrect methods were used as the determination for a moisture-related flooring failure.

Taking advantage of the difficulties experienced in the field, a proponent of RH probes stated "If moisture tests are so accurate, why are we still having problems?"

Taking advantage of the last 25+ years of RH probe testing, I would go further and ask "If RH Probes are so accurate, why have problems tripled since their inception?"

The answers lie not in the methods, but in the interpretation of the data and the applicability of the data.

On a Mission

I embarked on a quest to try and find some method, if it existed that could give meaningful results, simple to understand, implement and make economic sense.

I approached several manufacturers and approached by several manufacturers to either consult for them, or simply evaluate their methodology.

To put this in perspective, I was using the ONLY method I KNEW to be very accurate, but for the purposes of field usage, ease of use and affordability was completely impractical was gravimetric (oven method). This method has been used by many different industries and across a wide spectrum of materials, food stuffs, medicines, cosmetics and just about anything else where knowing the moisture content was critical. THIS (gravimetric) was my baseline.

I hoped for something that was at least along the lines where a reasonable and consistent correlation could be established.

The Turning Point

Even though I had recommended Tramex's concrete meter for measuring at time of installation as far back as 2010, I did NOT recommend it as an absolute when it came to testing the moisture content of concrete. This all changed when I received a study conducted in Finland by a very well-respected third party testing agency VTT.

The VTT Study as I refer to it, qualified several methods of moisture testing in their laboratory. What got my attention is they used the gravimetric as their baseline. This is something I had never seen in any study prior to this when evaluating a concrete moisture test method.

The qualifying devices consisted of RH probes, electrical, calcium carbide (the German Standard) and Tramex.

Jackpot!

When these devices and methods were brought into the field, they tested over concrete that apparently had a curing compound and areas with the curing compound removed. The first batch of results were taken after 14 weeks outdoor exposure. NONE of the methods, surprisingly the calcium carbide also fell into this group, were even calculably correlative with gravimetric except Tramex, which was nearly identical.

The bigger difference came at 28 weeks where the variability become more apparent and consistent with the theory of concrete hysteresis, even as the correlation of Tramex with gravimetric b3came slightly more precise.

I approached Tramex and asked if I could consult for them, as they now have proven what I was looking for and even exceeded my wishlist.

The Tramex Concrete Meter aligned elegantly with gravimetric, which as is the case with the currently used methods for coatings and flooring, takes 1-3 days or more to conduct the procedures properly, whereas Tramex takes literally minutes to perform, with instant and more meaningful data. These immediate results can catch transient moisture spikes that can occur in site conditions that would otherwise sabotage a perfectly good flooring installation simply because there is no other way to detect the presence of these transient spikes and/or moisture that can be absorbed by the concrete well after the initial site testing has been completed, irrespective of what type of moisture test was conducted.

Testing Results are ONLY Valid at Time of Testing

This caveat exists everywhere, yet when the results are most critical, there hasn't been a reasonable method to accurately monitor these changing site conditions.

There is no legitimate reason for any conscientious installer to NOT have this meter on hand. Unlike calcium chloride or RH Probes, this monitoring is NDT (non-destructive testing) and has no repeating costs. You aren't paying for multiple probes, calcium chloride kits, or dealing with disposal issues and site repair.

Moisture Absorption can occur in Minutes

In a recent site demonstration, a group of installers were present where the Tramex meter was used on a 40+ year old concrete slab. The concrete was tested with what was likely a curing compound with a measurement of 1.9%. The coating was ground off and the reading remained at 1.9%.

The group walked over to another area, and what was estimated to be 10-15 minutes later the same exact area gave a measurement of 4.3%.

This was a very graphic example of what can happen in a job site. Normally, someone would remove the coating, wait over night THEN test for moisture. That process would have given an incorrect baseline from the get-go, AND the ASSUMPTION would have been "the moisture originates from the concrete", when in reality, it originated from the ambient conditions. Another step in correcting a long line of misinterpretations!

Part 3 - We can Change the concrete to be suitable for any and all floors, but we HAVE to ask and know WHAT to ask for.