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.

powertrowel

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?

Moisture-Barriers-pic

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

1) PERM RATINGS.

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%.

2) TWO PART EPOXIES vs THE OTHERS

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.

IMG_9094

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.

The coalition of RH testers.

When it comes to Relative Humidity moisture testing for concrete slabs, the market leader in technology and related R & D is Wagner Meters.

You would expect such a market leader in vital flooring technology to reside in Chicago, New York or Los Angeles (that is, before business and industry started their mass exodus from the Hollywood State). In fact, Wagner reside is in one of those beautiful, green, quiet areas you find when touring the back roads of lower Oregon, replete with cute farmlets and trickling streams.

Jason from Rapid RH during presso
Jason conducts an RH Moisture Testing presentation at Shaw- (Image courtesy of Shaw Contract Group)

Not only have Wagner engineered some of the most innovative solutions for commercial moisture testing, they make a monumental input to improving the industry’s knowledge and skills base. Through a myriad of webinars, editorials and forums they ensure that the latest procedures are well publicised to an industry still trying to get its head around the need for moisture testing.

That was the reason for Wagner Meters’ Jason Spangler visit Down Under in August. I had the privilege of joining Jason and other industry folks at the premises of Shaw Contract Group (the importers of Wagner’s equipment), as he explained the importance of accurate RH testing in a changing industry.

I say “privileged”, because if you have spent years wading through the relevant moisture-testing information online and sought the right accreditation as we have here at Floor Test Australia, Jason has become somewhat of an orange-attired celebrity.

jason spangler
Jason in action

He is also proof of an adage we have been saying for some time: The Americans are the trail blazers in tackling this issue. In the USA, moisture-related flooring failures have been dubbed “the billion dollar problem”.  The spectre of ultra-expensive remedial problems is the perfect motivator to develop efficient, and scientifically-based solutions. The free market works well like that.

Jason’s recurring comment during his visit was this: “I’ve been involved in moisture testing and responding to flooring failure remedy for many years- the concerns and problems I am hearing here in Australia for the first time are identical to what we’ve heard in the USA.”

Here’s hoping we catch up quick. On behalf of a grateful industry, a big thank you to Jason for taking the time to come Down Under and help us out. We hope he enjoyed it, and to answer the most obvious question, he has told us “Yes, I did get to see a Kangaroo”.

So whose liability is it, anyway?

Floor Test Australia recently undertook the Lidcome TAFE information and accreditation session on subfloor inspection and moisture testing.

That the concrete slab subfloor needs to be moisture tested has been known for some time. Overall however, Moisture Testing for concrete subfloors in Australia is certainly an emerging (black) art, still not fully understood. The fact that Moisture Content via Capacitance Moisture Meters has given way to Relative Humidity (RH) Moisture Testing, is understood possibly even less.

There was a gargantuan amount of information to squeeze into one day, from the basics of Relative Humidity (RH) in the slab, to the mechanics of the Moisture Testing equipment, so credit must go to those who formulated the material. Still, many of the contractors and flooring retailers present were understandably overwhelmed at the implications of complying to a sub floor moisture test- that is, complying to the extent that they cover themselves as fully as possible in terms of liability.

So, whose liability is it anyway?

We live in an increasingly litigious society (and before you blame the Americans, note that Australia is actually more litigious per-capita than the USA), so doing it right first time is paramount. There are plenty of people out there ready and able to sue.

Lawyers can do that to you...

Lawyers can do that to you…

Not that most quality tradespeople and service providers haven’t always known that quality work is key- but, bearing all that in mind, nowadays there is increasing focus on how you record the information for future reference.

Having a $80,000 commercial vinyl installation blow up is obviously going to lead to the question of who is/was to blame.

At FLOOR TEST AUSTRALIA we know of a very telling resilient flooring installation failure which occurred in Queensland. The install was fine for six years. In the seventh year, the adhesive re-emulsified to the point that the floor level stunk out (it was a multi-story medical complex), as if the blisters in the floor weren’t bad enough. It was obvious to anybody with an ounce of common sense that the slab had taken on a major ingress of moisture long after the install, most probably due to a plumbing failure or the like. And yet, the installer was hauled in to contribute toward remediation- because he could not prove that the moisture levels were acceptable at the time of install!

So, it’s the installer’s responsibility to test the subfloor concrete slab for RH, right? Not necessarily. Large commercial projects have many stakeholders from installers, architects and project managers et al. Communication between all parties will obviously help produce a quality job. However, it stands to reason that whoever has taken the trouble to capture accurate figures describing the moisture condition of the slab prior to install, and acts upon the information accordingly, will reduce their liability significantly.

We have been involved in cases where the flooring contractor has tested the slab, but advised the project manager to get a second opinion. This is quite wise, especially if there are pressures from the final customer to fast-track an installation. In such cases, and independent test can absolve the the project manager and his installer from a potential strained relationship with the customer- that is, the customer can see that it is an independent, qualified voice expressing concerns about rushing into a floor install- not merely a contractor trying to squeeze more money out of them, or postpone a job to accommodate other work.

Of course, it helps to ensure that customers are advised before any plans are drawn up that there is the potential for sub floor issues and associated costs such as testing, mitigation, drying etc. This can often be covered as PC items.

So whose liability is it? We can’t answer that. But we can be sure that whoever owns the most information, and acts on it correctly, will have less need to worry about that question.

Is your concrete slab ready for flooring?

WHY should concrete slab moisture be an increasing problem for flooring installations over the last 5 or so years? Why is Relative Humidity (RH) Moisture Testing for Concrete Subfloors now in demand more than before?

Are concrete contractors using more water? Can we blame them for the spate of failures of late?

Well, no, of course not. They have to use more water in some cases- where excessively dry conditions can cause the concrete to crack, for example. Using more water helps the curing, and therefore the strengthening process of concrete. In fact, for major structural projects, engineers are using a combination of drying rate measurements and heat measurements in concrete structures to determine its overall strength. It’s called the maturity method. But that’s another story, for now (fascinating though it is).

Indeed, the water in concrete’s original pour is a part of life for flooring installations and we have known this for some time.

Certainly the “greening” of adhesive and other products has made them more susceptible to moisture and alkaline attack. There is little doubt in the industry that this is a prevalent issue.

adhesivefailure1

Green building codes and lower-VOC products are also a part of life, and adaption to them is required. But this alone is not the problem either.

Flooring industry boffins (that’s not a rude word by the way) has always agreed that moisture is an issue which needs to be tackled, but have not really agreed on how to measure it.

With almost 12 years in the timber flooring industry, I know that the timber folks were well accustomed to, and dependent upon, the “Moisture Meter” (electrical resistance) way of measuring. It was great- because the parameter was simple (nothing over 5.5% moisture content, down goes the floor). Even better than that, the meters were easy to use. Turn =\’em on, hold ‘em down, and look at the little needle.

What changed? Well, two things: It was always known to be the case that these measurements only scratched the surface of the concrete- literally- just a few mm’s. Also, it only measure the water which was THERE, rather than the water which HAD NOT FORMED YET. But only recently was it decided that this was a problem. Or, perhaps, it was that a better way was found.

Meanwhile, increased use of additives in concrete mix (green influence again) such as fly ash (waste material) was found to be skewing the resistance meter’s readings.

Only by measuring humidity deep within the slab, would a reading be found which would best paint the picture of what a flooring installation was most likely to experience if laid down at that time.

If only things could stay simple. But the Devil is always in the details, and Relative Humidity (RH) Moisture Testing for concrete subfloors has emerged as the method most widely acknowledged for its accuracy and relevance.

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