R.H. Readings In The U.S.A

(Post title best sung to the tune of “R.O.C.K. in the USA” by Johnny Mellencamp- in case you didn’t get it. Well, it seemed okay when I wrote it in my head…)

This may be a slightly shameless plug, since we use the same equipment for the same reasons, but here’s a hat-tip to a mate in the USA who knows a thing or two about concrete moisture. An interesting article.

Click here to read



Surface RH% Test Standard Withdrawn.

If you’re privvy to the science behind the in-situ method of moisture testing, and why it is the most accurate and researched way of predicting the slab’s moisture condition, this would come as no surprise to you.

ASTM F2420-05(2011)- “Standard Test Method for Determining Relative Humidity on the Surface of Concrete Floor Slabs Using Relative Humidity Probe Measurement and Insulated Hood” has been withdrawn by the standards committee, as of December 2014.


A recap: The “hood” method as it is known (because the Standard’s full title is a mouthful) aimed to capture the RH condition above the slab. AS 1884-2012, Australia’s Resilient Flooring Standard, prescribed ASTM F2170-2012, the in-situ probe at-depth method, to accurately measure the RH% condition of the slab. However, it referenced ASTM F2420-2011 where drilling into the slab is not possible, due to in-slab heating elements or such like.

The problem is, the two methods are very different. Even the standard itself acknowledged that the hood method only captures the RH% condition at the time of the test. The in-situ method is a real predictor of future RH% potential if a sealed floor is placed on that slab.

It was also recognised that the hood method only captured the RH% condition in that portion of the slab. In-situ RH% tests capture the “worst case scenario”, that is, to what RH% the slab would equilibrate to across its surface if it was sealed by a floor.

The hood method was also notorious for drift. While the hood was given the same equilibration period as in-situ (72 hours), the standard itself prescribed a maximum amount of drift in the reading allowable before the reading should be disregarded, and you have to go back later and read it again. Much later. Floor Test Australia has seen this first hand. The drift could be up or down, which also suggests the hood method was more instantly susceptible to environmental changes.

The standards committee actually stated that drift may not settle until up to 70 days after the hoods were placed. We don’t know of many construction jobs which can wait 70 days for a go/no-go on the flooring decision.

Precision and bias tests also showed a large disparity between different hood products in equal environments.

Obviously, the obsolescence of ASTM F2420-05 could be detrimental to those who simply cannot drill into the slab. In these cases, contingencies must be found, such as accurate scanning for in-floor elements to determine drilling locations. It certainly highlights that the need for accuracy in measuring the slab’s moisture.


Perception is everything- Why you should use independent, certified moisture testing #2

Of course, not all flooring installations require certified, independent moisture testing for the concrete subfloor. In fact, you might think not all installations require any testing at all, which we discussed in an earlier post .

If you are installing 50 square metres of carpet in a residential job, it would probably suffice to undertake the testing yourself- especially if it’s just you and the homeowner. No middle men, no consultants, no lawyers, construction company boffins or twenty different stakeholders asking twenty different difficult questions.

Sadly, not all jobs are this simple. There are as many reasons to have independent, certified moisture testing as there are people who need to be assured that it is not as simple as just…slap a floor down and walk away.

Put simply, when you tell that construction company that they need to pay an extra $40,000 to apply moisture mitigation on that large-scale commercial project- mitigation which they will never see, and whose benefit they may never know- they will want to know why. And if they don’t, their customer certainly will. Especially if that customer is a government department.

When you tell them it’s because the moisture is too high and the floor could “blow up” at a later date, their approach will most likely be “of course you will say that, you get to charge me an extra $40,000”!

Independent test results are just that- independent. Demonstrably, and provably, free of commercial affiliations and conflict of interest- perceived or otherwise (in the business world, perception is everything!).

Floor Test Australia  have frequently provided testing on sites where testing has already been done. This is not unusual, especially on public infrastructure projects in tourism, healthcare and education. It’s reassuring to see more and more flooring professionals undertake the testing (providing they do it properly), but it proves that, rightly or wrongly, the decision makers in the project often take a dim view to results that mean more expenditure for them. They need to be assured in every possible way that the expenditure is for their own benefit.


Power Troweled concrete- friend or foe?

Here’s a question- if you’re a flooring installer, do you get to make recommendations to your client before the concrete is even poured?

In a perfect world, you would be able to sit in on the discussions between architects, construction heads and specifiers and talk about the concrete stuff. Then you’d know that, by the time you’re called in to lay the floor, the concrete surface is all ready for you and requires minimal preparation for you to do your stuff.

But it’s not a perfect world. You know that the concrete folks have recommended nice water content in the mix to ensure high-strength curing, and a power-trowelled finish to ensure it’s smooth to touch and pleasing to the eye. And somebody’s paid for all that.


Then you arrive. You have to enlist some expensive and time consuming grinding to a specification which gets rid of that sexy power-trowelled surface, because there’s no way your adhesive is going to bond to that. In fact, neither will your moisture suppressant/ mitigation product, when you find that the tight, smooth, power-trowelled surface has prevented the slab from drying much, if at all. And you have to pay for that.

Wouldn’t it be better if neither needed to be done at all? Somebody would save a lot of money, and whoever advised them to save that money would be quite the hero.

Excessive power trowelling is the bain for flooring contractors. Not only does the “tightened” surface restrict a good drying rate for the whole thickness of the slab, it’s also another reason why capacitance Moisture Meters’ surface readings cannot be relied upon. The less-open and porous nature of the first few millimeters will generally read low.  Couple that with a low drying rate, the moisture deeper in the slab will tell a very different story.

Here’s another tip: Grinding ain’t grinding. A surface grind to remove the “feathery” imperfections which can be left from a myriad of other trades or levelling compounds added to the surface- isn’t necessarily going to open the pores of the surface as required. Some homework is required on the specification of grinding!

It might not be possible to have input into the entire building process,  to the extent of requesting a desired finish of concrete. However, as major projects are becoming more professionally managed, those at the “end” of the process (such as the humble flooring installer) are more increasingly consulted. If you’re lucky enough to be one of them, make the most of it and put in your two bobs’ worth on power trowelled finishes.

Of course, this is not to blame the concrete guys. They are asked to produce a flat, smooth surface and the power trowel process is the best way to do it. If they under-do it, the job may not be accepted. They trowel as much as possible, “just to be sure”. It’s the specifiers, architects and project managers who need to be fully aware of the pitfalls for the flooring professionals.

So you’re going to mitigate…

That’s a great idea. You’ve quoted high enough, or have PC allowances, so you’ve decided that you’re going to slap down a moisture sealer/suppressant/barrier, just to be sure that slab will behave itself when a floor goes on top. Surely an accurate and relevant moisture test is not required, right?


Well, not really. Bear with me as I explain two major considerations.


No, this is not about the quality of a hairstyle popular in the 70’s.  As oils ain’t oils, so moisture barriers ain’t moisture barriers. Traditional two-pack epoxy Moisture barriers all have permeability ratings. That is, how “gappy” is the matrix structure of the cured sealing material, in that it can allow material to pass through it at a microscopic or minute level. A suitable metaphor would be to compare firing a pellet gun at a wire fence or a metal sheet. The slug probably won’t pass through the metal, but it probably will fly through the wire fence. Some might use the term “porosity”.

Perm ratings measure in the amount of mass (usually in grams) which can pass through a given area of the cured material (usually in square metres) PER a given period of time (usually 24 hours). Perm ratings are measured against their own Standard, but we won’t go into that right now.

However, it’s difficult to directly compare perm ratings for each product, because the Standards dictate how to determine the rating, but not how to express it. Some will give the perm rating for single hour periods, but strictly under certain temperatures and RH levels. Some state a rate per 24 hour periods.

So there are more “solid” products with greater moisture suppressing properties, and lesser ones.The differences are generally reflected in the costs of these systems which can translate to between $8 per square metre to $20 per sqm and above.

So here’s the trick: A moisture barrier is not a cure-all, because some are only rated to perform UP TO A CERTAIN MOISTURE LEVEL EXISTING IN THE SLAB- and most of them will stipulate an RH% figure. Some will perform at over 95%, some no higher, some up to 98%.

Remember, with any permeability, a barrier simply slows down the release of moisture vapour pressure to the point at which the flooring/ adhesive can handle it. If the humidity deep in the slab is high enough, the pressure will be higher. FLOOR TEST Australia have tested many a slab which should be moderate, yet reads 99%.


There are other emerging moisture treatments besides two-part epoxy film builds. Actually, some of them have been around for several decades and have been re-invented, or have crossed over from other applications (such as concrete surface densifiers) and regarded by some to be useful for keeping moisture down. They often boast of being single packs, easy to apply, dry in an hour, flooring able to he adhered within a few hours, and often with extremely low VOCs.

Their technical names include “alkali silicates”, or reactive /colloidal silicates. They react with existing moisture and lime (calcium hydroxide) in the cement mix, to create a gel-like or crystalline substance in the pores of the concrete. This is the effect which made them useful surface densifiers. Some of the product claims range from pragmatic to extremely bold, implying that they will solve all moisture problems.

It is very difficult to wade through the mire of political/ commercial interests which dominate the debate raging over these types of products and remain objective. While Floor Test Australia is INDEPENDENT of those things, we acknowledge the time and money put into researching moisture-related flooring failures by many commercial entities whose only interest is preventing flooring failures.

Efflorescent salts on concrete surface treated with silicates (magnified). Pic courtesy of Ardex Australia

Efflorescent salts on concrete surface treated with silicates (magnified). Pic courtesy of Ardex Australia

Indeed these are useful products in their own sphere. As I mentioned earlier, some are adapted from surface densifiers which are used to produce spectacular concrete grinding effects. However, like the epoxies and their different perm ratings, these products have their catches as well.

Firstly, since the sole function of the product is to react with the calcium hydroxide (CSH) in the cement mix to be effective, what if there is not sufficient CSH in the mix to react with? There are other elements within concrete mixes which can react with CSH and therefore reduce its availability for the silicate treatments to work.

We also know that colloidal silicates can cause efflorescenceThat is, calcium carbonate and other alkaline deposits from the cement mix in the slab can form on the surface over time due to the silicates reacting with Carbon Dioxide in the air. This can definitely compromise the performance of an adhesive. Can the manufacturer provide a (warrantied) procedure for removing these deposits? 

Being a different method of moisture suppression, many of the adhesive manufacturers who create a whole moisture barrier/ adhesive system, will not warranty their products over these silicate-based treatments. The silicate product may have its own warranty, but that doesn’t mean they can warranty the adhesive and the flooring itself. Nonetheless, some of the silicate products have made good associations with other manufacturers and specify which adhesives work best over their product.

Like epoxies, these products also require a degree of surface porosity in order to be effective. The rule of thumb is- if the surface is not porous enough to take any moisture treatment, it’s not going to accept a flooring adhesive. Those power-trowelled (“helicopter”) finished surfaces can be a nightmare for any moisture mitigation or floor adhesive product.

Again, there are many different camps with many differing opinions on epoxies vs silicates. But anyone who says that you don’t need a verifiable moisture test before any major flooring installation, regardless of a) whether moisture mitigation is planned and b) what mitigation product will be used…. is kidding themselves.

Why you should use independent, certified moisture testing

Here’s a great article by one of the USA’s most learned gurus on subfloor preparation, Peter Craig.

The article is in FCImag- a leading US publication for Floorcovering installers, it’s free to register.

Some quotable quotes:

“When a flooring failure occurs, one aspect of the process that is scrutinized is the moisture testing that was performed prior to the installation. … Who performed the tests? What methods and equipment were used? How were the test sites prepared? Under what conditions were the tests performed? How many tests were performed? Was the equipment properly calibrated? … In all too many cases, the results of the moisture tests are discredited due to procedural errors on the part of those who performed the tests.”

Certification is crucial to avoid these common mistakes. (to)… provide more consistent, accurate and truly representative test results that will allow those responsible to make better decisions as to when a concrete floor is ready for a floor covering.”

Click here to read the article.

Goo in the science lab

We’ve mentioned before that unchecked RH at-depth can cause a litany of grief even long after the floor is installed.

Floor Test Australia recently conducted a test for a private school.

The vinyl install was completed in 2010. The installation was top quality.

Fast forward to 2013, when adhesive began to ooze through the seams in the vinyl. When squares were cut out, the adhesive was as fresh and sticky as the day it came out of the tub. We’ve talked about re-emulsification before, too.


Here’s the interesting bit: The installer did the right thing- they moisture tested prior to install. But that was 2010, when everybody used capacitance meters. The readings were fine. This implies;

a) that moisture content % is indeed irrelevant as established by the AS 1884-2012 findings

b) that the slab was fine at the time but moisture was introduced after the fact

c) both of the above

Either way, it stresses the importance of testing prior to install, if you want less chance of having to test after a failure to try to shift liability for the failure elsewhere.