In terms of moisture, concrete is counterintuitive. When we think about concrete, many of us picture it as a dry, hard material; something that’s resilient to rain, snow and moisture. Unfortunately that’s not the case. Concrete is wet when it’s mixed, and is a porous material once it’s cured. Unless it’s been coated or protected, concrete will absorb moisture – even humidity from the air – and holds some level moisture in it at all times. That said, only so much moisture is allowed. Many finishes installed on top of concrete, such as flooring and coatings, require that moisture content in the concrete stay below specific moisture levels while work is in progress. The moisture content in concrete can’t be too high either; if concrete is too moist, it can crack, spall and fail in a number of ways. In turn, concrete moisture monitoring is important for a variety of reasons! Let’s get into the details of why concrete moisture monitoring is so critical during construction and building inspections, along with our top picks for the best concrete moisture meters on the market.
Navigate:
- Concrete Moisture Content: An Overview
- Does Concrete Absorb Moisture?
- How Does Moisture Affect Concrete?
- Moisture Content vs. Relative Humidity In Concrete
- Signs Of Concrete Moisture Damage
- How Do You Measure Moisture In Concrete?
- Best Concrete Moisture Meters: Our Top Picks
Concrete Moisture Content: A Brief Overview
Before we go any further, it’s important to draw a distinction between two different scenarios – wet vs dry concrete.
When concrete is being mixed, the amount of water in the mixture relative to cement – known at the cement-water ratio – can be very high. This ratio is calculated by dividing the amount of water (in pounds or kg) by the amount of cement in a given batch of concrete. One cubic yard of wet concrete mixture will consist of hundreds of pounds of water!
Knowing this, it’s important to also understand the concrete curing process. The moment concrete is mixed, it begins drying. Because of this, concrete must be poured and finished quickly. In the hours, days and weeks that follow, the new concrete will evaporate a huge portion of that water.
Concrete takes 28 days to fully cure ie. to reach full design compressive strength according to the American Concrete Institute code 318 (via ACI.org). That said, it can usually be walked on within an hours and coated or built upon within weeks.
Even after reaching full compressive strength after 28 days, concrete will still retain some moisture inside despite being “dry”. Depending on how recently it was poured, the humidity in the air and any vapor within the concrete, moisture and humidity levels can vary quite a bit. This existing moisture within fully-cured concrete is the moisture content we’re interested in!
Does Concrete Absorb Moisture?
Although we covered this in some detail already, the answer is YES! Concrete is an extremely porous material – like a sponge.
Concrete absorbs moisture when it rain or snows, but it also absorbs (or evaporates) moisture depending on the relative humidity levels in the atmosphere, even on a day with no precipitation. In humid environments, concrete will absorb moisture out of the air, while the moisture within concrete will evaporate in dry climates.
How Does Moisture Affect Concrete?
Moisture can affect concrete in a number of ways. Just as importantly, moisture can affect concrete from the moment it’s poured until the day it’s no longer in use!
What happens if fresh concrete gets wet? As we know, concrete needs water in the mixture to cure properly. ‘Wet curing’ involves intentionally spraying down the fresh concrete periodically in the days after a pour (beginning several hours after completion) to prevent the water from evaporating too quickly. That said, fresh concrete can still be damaged by excess rain or moisture if it’s not protected.
The surface of fresh concrete can be permenantly weakened after receiving rain due to the cement being washed out of the mixture. In turn, the top layers of concrete may begin to crack and peel away in thin flakes over the entire surface. These weakened top layers will also continue to absorb moisture more easily in the future.
What about finished, fully-cured concrete? Excess moisture is still problematic. While exposed concrete surfaces should be coated or otherwise protected, these coatings aren’t perfect – they have a limited lifespan and can still allow excess moisture into the concrete if not applied properly. If concrete cracks excessively due to settlement or damage, both coated and uncoated concretes are equally at risk for damage if too much moisture gets inside.
Moisture Content vs. Relative Humidity In Concrete
Although new concrete may be considered “dry” a few weeks or months after it was poured, it could still be retaining moisture inside in the form of water from the mixture, as well as vapor from humidity in the air. The two are often intertwined.
Depending on factors like time (days, weeks), relative humidity (RH) and the depth of the concrete where a reading is taken, moisture readings can vary – even in the same section of concrete!
This is because moisture content is not evenly spread through any particular section of concrete; the relative humidity near the surface will generally be less than the RH a few inches deeper, given that moisture closer to the surface can evaporate more easily.
This is important to consider before applying any finishes on top of the concrete. Since the vapors inside the concrete will eventually “want” to come out through the surface when atmospheric temperatures and humidity levels change, the moisture trying to exit will ruin any finishes installed over it in the process!
Just to reiterate a bit further, relative humidity (RH) levels in concrete are particularly important for finishes like:
- Flooring – Tiles, Wood, Laminates, Etc.
- Deck Coatings
- Waterproofing – Liquid & Sheet Membranes
- Paints
Before installing any of these types of finishes, checking RH levels inside the concrete is very important! We’ll get more into that below.
Signs Of Concrete Moisture Damage
Concrete moisture damage comes in many forms. Like we said earlier, signs of moisture damage in concrete can appear any time between placement and years after curing.
As we described above, the surface of freshly poured concrete will begin to scale and flake away in thin pieces soon after getting overly wet.
As for signs of concrete moisture damage in finished concrete, there are many to be aware of:
- Decay: If the concrete can be chipped or broken apart using minimal force, there’s a good chance that concrete moisture damage has occurred.
- Moisture In Cracks: If there’s water dripping or flowing through a crack in the concrete, especially in walls and ceilings, it’s likely that water damage is occurring internally.
- Rust Spots: Rust spots in concrete often indicate that the steel reinforcement inside (rebar, wire mesh, etc) is getting wet and rusting. This can be easy to spot in some cases, because the rust damage will follow a similar pattern to the steel inside. The steel will continue to erode over time, which causes further damage.
- Spalling: A broad term that includes breakage, peeling, scaling, section loss, etc.
Concrete moisture damage is usually easy to see visually, but what about instances where concrete moisture levels could be too high, but there’s still time to remedy it? What about installing coatings or other finishes on non-damaged concrete, where the moisture levels must fall within a particular range for proper installation?
That’s where concrete moisture monitoring comes into play.
How Do You Measure Moisture In Concrete?
There are a few methods of concrete moisture monitoring out there – some more scientific than others.
Below are a few of the most accurate and commonly used standards in construction:
- ASTM International Standard F2170: “Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes”.
- ASTM International Standard F2659: “Standard Guide for Preliminary Evaluation of Comparative Moisture Condition of Concrete, Gypsum Cement and Other Floor Slabs and Screeds Using a Non-Destructive Electronic Moisture Meter”
So what’s the difference?
- F2170 involves taking readings of relative humidity within the concrete itself using a bore, probe or some other means.
- F2659 involves taking surface-level moisture content readings though non-destructive means.
As you can imagine, each of these methods has advantages and disadvantages depending on the application.
Best Concrete Moisture Meters: Our Top Picks
Lastly, let’s explore three popular tools and kits used for various types of concrete moisture monitoring. Each of these tools is unique in its’ features and compliance with various ASTM standards. Let’s discuss!
Bluetooth App-Based Relative Humidity Monitoring: DeFelsko PosiTector CMM IS Test Kit (ASTM F2170)
Here are some highlight reasons why this device may be a great fit for concrete moisture monitoring on your projects, specifically for relative humidity (RH) monitoring:
- Wirelessly measure relative humidity and temperature in concrete floor slabs.
- Easily collect and report RH measurements in conformance with ASTM F2170 using their mobile app.
- In situ smart probes are reusable and weatherproof.
- Probes remain powered on for up to three weeks and broadcast wirelessly via Bluetooth while in situ.
- Combined sleeve and probe design simplifies the ASTM F2170 installation process; does not require consumables.
- Uses common coin cell batteries.
- DOES require coring holes into concrete.
Non-Destructive Moisture Meter: Tramex CME5 Concrete Moisture Encounter (ASTM F2659)
If you need a way to perform quick, non-destructive concrete moisture monitoring, here are some highlight reasons why this device may be a great fit for your projects:
- Non-destructive concrete moisture meter (complies with ASTM F2659).
- Measures up to 3/4″ deep into the slab.
- Provides 0 to 6% concrete moisture reading range.
- Measures moisture content by low frequency electronic signal via electrodes in the device.
- Battery-powered & less than one pound (approx. 12 oz.).
- Connect to your meter using Bluetooth and iOS / Android mobile app for continual development and integration of apps and reporting.
Dual Concrete Moisture Meter: Tramex CMEXpert II Digital Concrete Moisture Meter (ASTM F2659 & F2170)
If you need a dual-purpose concrete moisture meter that can perform both non-destructive moisture readings and measure relative humidity within the concrete, here are some highlight reasons why this device may be a great fit for your projects:
- The CMEX 11 Moisture Meter is designed for the instant and precise measurement of moisture content in concrete.
- Measures up to 6.9% Moisture Content in Concrete.
- Hold function “freezes” meter reading when inspecting areas where the meter face is not visible.
- Attaches to a relative humidity Hygro-i ® probe for in situ testing of concrete to international standards BS 8201, 8203, 5325 & ASTM F2170 (optional and additional).
- Measures 0 to 99% relative humidity using optional Hygro-i ® RH probe.
- Battery-power and less than one pound (approx. 11 oz.).
Optional Hygro-i ® Probe (Sold Separately)
In Closing
I hope this article has been clear, comprehensive and informative. If you have any questions about what we’ve covered, feel free to comment below! Thanks for reading.
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