There are some things that just need to be done a certain way.
For concrete moisture assessment, whether in a large-scale commercial venue or a residential basement, a singular technique stands out: the ASTM F-2170.
Though its title might not be immediately revealing, the ASTM F-2170 is recognized as the benchmark for accurate moisture measurement in concrete.
So, what does the ASTM F-2170 mean and why does it set the bar for measuring moisture in concrete?
In this article, we'll dig into exactly that, as well as:
- Completing concrete moisture tests to the standard
- The most important application for ASTM F-2170-compliant testing
- & more
ASTM F-2170 | A Closer Look
Though the methodology of testing relative humidity (Rh) in concrete the ASTM F-2170 employs had been used in Europe for a few decades prior, the standard was brought to the U.S. in 1999 and published in 2001.
Born out of a need for a more accurate & reliable moisture measurement method for concrete slabs and to get the upper hand on floor failures, the ASTM F-2170 took a new approach to qualifying moisture presence.
But first, a quick step back.
Prior to the adoption of the ASTM F-2170, those testing concrete for moisture relied on several different methods. In addition to accuracy, the problem with other methods was consistency with results. Take, for instance, the calcium chloride method – what the ASTM F-2170 replaced as the standard for concrete moisture testing.
Though it produced results, calcium chloride moisture tests didn't always provide a true representation of moisture presence. The testing method involves putting an anhydrous calcium chloride crystal (a salt) onto the surface of concrete and waiting at least 72 hours. During that time, the crystal absorbs moisture and becomes heavier. At the end of the test, the crystal is weighed. Suffice it to say, a higher weight means more moisture exposure.
The trouble with this moisture measurement methodology is the results are indicative of all the moisture the crystal was exposed to, which can be more than what passed through the concrete. For instance, should a high humidity or even rainy day occur – more moisture is likely to pass through the material. Consequently, even floors that checked out with acceptable moisture levels still failed later as the test was inadequate (we'll come back to this later).
Back to the ASTM F-2170 ...
Unlike other testing methods, quantifying moisture in concrete under the ASTM F-2170 goes under the surface to take a different type of measurement. More specifically, the standard uses the in situ method (more on putting this to practice later) to perform concrete Rh tests from inside sealed holes in a slab using a hygrometer probe.
Why is the in situ relative humidity testing the preferred way?
A few reasons:
- From inside a concrete slab in a controlled microenvironment, there's little chance of external factors, say, a change in a room's humidity, impacting results.
- The moisture you can't see usually poses the biggest problem. In the case of concrete, its porosity allows water vapor (something that's not obvious to the naked eye) to travel through it.
- It's nearly impossible to test concrete's moisture accurately with a moisture meter. As pin-type moisture meters rely on electrical conductivity and can only take surface-level readings. What's more, concrete’s electrical properties vary depending on its composition, meaning a pin-type meter is unlikely to give you a true indication of moisture. Pinless – or non-invasive meters – generally can't take readings more than ¾ inch below the surface. And rather than quantifying moisture content percentages, pinless meter measurements only qualify moisture presence and help you determine areas of concern. That’s not to say moisture meters don’t have a place in testing concrete for moisture – they can help you do a quick evaluation and determine areas where a closer look is required.
- As moisture moves through concrete at a gradient, representative results require gathering data from multiple points. The in situ method using the ASTM F-2170 standard sets the minimum number of probe insertions needed per 1,000 square feet.
- Moisture meters are for rapid evaluation, and whilst in situ takes 24 hours to complete a test, it’s considerably less time than calcium chloride testing. However, in situ testing can go on as long as needed, just as long as the microenvironments the probes are in stay protected & undisturbed.
Testing Concrete Humidity to ASTM F-2170 Standards
The in situ concrete Rh testing method is a relatively straightforward process.
After identifying an area of concern within a concrete slab, properly administering an in situ test to ASTM standards requires using a hygrometer, probes, and following seven steps:
- After using a pinless meter to locate areas with the highest potential for moisture, drill three holes for the first 1,000 square feet in the area of a concrete slab being investigated to a depth equal to 40% of the slab’s thickness. You’ll need another one hole per 1,000 square feet after.
- Clear the holes of dust and debris – use a wire brush to free up any loose particulate and then vacuum each opening.
- Visually inspect the bottom of each hole to make sure you haven’t drilled into the heart of a piece of coarse aggregate (e.g. gravel). If more than half of the hole’s base is coarse aggregate, drill a new opening.
- Set your Rh probe sleeves to the correct depth and insert them into each hole.
- Insert Rh probes into their respective sleeves and place a cap to seal each opening.
- Wait 24 hours for the probes to equilibrate with their microenvironment’s relative humidity.
- After 24 hours, take & record Rh readings using a hygrometer.
A Word on In Situ Probes for Concrete OptionsReusable and disposable hygrometer probes are both used for concrete slab Rh testing. Though reusable probes are typically more expensive than their disposable counterparts, they offer two primary advantages that are hard to ignore. From an economic standpoint, reusable probes can be used multiple times, making them more cost-effective over the long term. From a technical standpoint, reusable probes are more accurate than disposable because of the type of sensor technology they employ. |
When ASTM-Compliant Concrete Rh Testing Matters the Most
While there's never a wrong scenario to check moisture in concrete if there's a concern, there's one where the test matters the most: before installing flooring overtop concrete.
Why? That takes us back to the reason the ASTM F-2170 came to be: the need for a standardized and accurate way to gauge moisture presence in one of the hardest building materials.
Think of your favorite big-box retailer.
Chances are its floors are tile – tile that's installed overtop a giant concrete slab. If that slab is improperly tested for moisture and if it doesn't have an appropriate vapor barrier, the chance of a flooring buckling or lifting (tile tenting) somewhere is all but certain at some point. Diagnosis of the issue and the accompanying repairs are very costly, not just from a labor standpoint, but also because it may require shutting down areas of the store.
The same holds true for any part of a building with a concrete base: be it a home or other commercial property. Concrete slabs that aren't tested to ASTM standards are an expensive repair bill waiting to happen.
ASTM F-2170 | Providing Clarity for Moisture & Concrete Slabs
As the standard for gauging moisture in a concrete slab, the ASTM F-2170 brings clarity to a process that was once inconsistent and unreliable for decades.
Providing a more accurate and reliable approach to measuring moisture in concrete, the ASTM F-2170 provides a way to confidently assess the integrity of a slab floor.
Take a Deeper Dive in Concrete Slab Moisture Testing
Download our guide to checking moisture in concrete slabs with a hygrometer:
