Concrete is a fairly ubiquitous material for construction projects. In homes and most offices, concrete is used for foundations and subfloors—many buildings even use concrete for major load-bearing walls. With concrete being such a common building material, professionals in the construction, restoration, and home inspection industries all need a means of accurately detecting moisture in concrete.
Some companies offer so-called “concrete moisture meters,” which can provide a qualitative, surface-level reading of concrete moisture. However, these concrete moisture meters do not provide accurate, quantitative measurements of moisture in concrete. This is because the composition of concrete mixes — even ones made by the same company — can vary greatly between batches, meaning there is no consistent set of physical properties that a concrete moisture meter could be calibrated to.
So, how can you accurately measure moisture in concrete structures? Here are a few tips to get you started:
Tips for Testing Surface-Level Concrete Moisture
For many home inspection and restoration applications, a surface-level test of concrete moisture may be enough to satisfy the demands of the job—or, at least, inform you if further testing deeper in the slab is warranted. So, to quickly get a rough idea if concrete near the surface is wet, there are a few things you can do:
- Use a Reference Scale Meter and Test a “Dry” Sample of Concrete First. Reference scale moisture meters can provide a quick and reliable “wet/dry” indication for concrete. Simply test a bit of concrete you know to be dry with the meter and make a note of the reading given. Then, use the meter to test the rest of the concrete—if a reading is significantly higher than the sample you tested, then that section of concrete is probably wet and needs more exhaustive testing per the ASTM F-2170 standard.
- Consider Using Pinless Moisture Meters. Pin-type meters can only test the material between the pins for moisture. Given the hardness of concrete, this can be problematic. Using pinless moisture meters allows for faster testing of larger sections of concrete since the scanning plate only needs a flat surface to work. These meters can scan just below the surface layer of concrete without much prep work, so taking readings in concrete is easy. Just be sure not to drag the scanning plate across the concrete, as this can damage the meter and compromise its accuracy.
- If Using Pin Meters, Bring Ductile Nails. If you need to use a pin meter, want to get even deeper into concrete than you could with a pinless meter, or are trying to find out how deep a moisture pocket in concrete is, bring some ductile nails. You can drive two nails into the concrete, then run wires from the tips of the meter’s pins to the nails (or, if the nails are close enough together, just touch the pins to the nails—one pin per nail) and take a reading. If you’re trying to determine how deep a moisture pocket is, drive the nails in little by little and take a reading every 1/4” or so. This can help you to determine how deep a moisture pocket is in concrete.
- Calcium Chloride Solution Testing. One way to get a relatively reliable assessment of moisture near the surface of a concrete floor is to use the ASTM F-1869 calcium chloride test. These tests determine the moisture vapor emission rate of concrete, and can provide a decently reliable estimate of moisture conditions in the surface of a concrete slab. However, they can be greatly affected by ambient humidity conditions, so be sure to use a thermo-hygrometer to test the relative humidity (RH) near the testing area.
While these tips can be useful for testing surface-level moisture, there may be times where you need to test moisture conditions deep in a piece of concrete—and, here, you’ll need the most accurate results possible.
Tips for Following the Best Way to Measure Moisture Deep in Concrete Slabs
When measuring moisture in concrete, the best and most reliable method is to use the ASTM F-2170 testing method. Under this method, you’ll use a thermo-hygrometer with in-situ probes, along with a series of prepared holes, to get readings of relative humidity deep in the concrete slab. Testing RH deep in the slab is crucial for determining how much moisture the slab is likely to release into surrounding materials, helping you prevent (or at least anticipate) moisture issues.
Here are a few tips for detecting moisture in concrete per the ASTM F-2170 Standard:
- Bring Safety Gloves and Goggles. Part of the standard’s requirements involve drilling holes deep into concrete (at least 40% of the slab’s thickness). When drilling concrete, flying chips of concrete and dust are going to be an issue, so be sure to bring eye and hand protection to avoid injuries.
- Measure the Total Area of the Concrete Slab to Be Tested. Odds are, you’ll have access to blueprints telling you how much surface area the concrete has—but don’t just rely on that. Measure the area of the concrete floor you’re testing yourself so you know exactly how large it is. This way, you’ll know exactly how many holes you need to prepare (three holes minimum for the first 1,000 sq. ft., and another hole for each additional 1,000 sq. ft. beyond that).
- Use a Rotary Hammer Drill with Three or Four Cutting Edges. This kind of drill and head combination will help ensure a smooth hole is created—making it easier to fit a sensor sleeve into each hole. 5/8” size drill bits are preferred for Delmhorst’s sensor sleeves.
- Take Multiple RH Readings at Each Hole. To help avoid skewing any results with an anomalous reading, be sure to take several measurements of RH at each hole you test. This way, if one reading is off, you can easily determine this fact.
- Consider Drilling Extra Holes. Keeping to the bare minimum of three holes for up to 1,000 sq. ft. of concrete (and just one more for each 1,000 sq. ft. after that) can mean having gaps in your testing area. Consider making additional holes so you can evenly distribute them throughout the testing area and be a bit more thorough.
- Choose Your Thermo-Hygrometer Carefully. Having the right thermo-hygrometer and sensor probes can make a huge difference in the accuracy of your concrete moisture testing. Ideally, you’ll want a model that has a minimal level of sensor drift (2% or better), so you can get reliable readings.
Need help finding the right thermo-hygrometer to use for your ASTM F-2170 testing needs? Contact the experts at Delmhorst Instrument Co. today. Or, check out our guide to flooring systems at the link below to learn more about using thermo-hygrometers for concrete moisture testing.