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Rapid RH
- What is Relative Humidity in concrete?
- What are acceptable levels of relative humidity?
- How many relative humidity tests should I use on each job?
- What is the correlation between Relative Humidity percentage and Moisture Vapor Emission Rate (lb/1000 sq ft/24 hr) measured with calcium chloride testing?
- When talking about moisture testing, what does equilibration mean?
- What are the advantages of Wagner Meters Rapid RH™ Smart Sensor Technology over other relative humidity instruments?
- How important is sensor calibration to the accuracy of the readings?
- Can I use the Rapid RH™ even if the HVAC isn’t on?
- How long does the battery last in the Rapid RH™ Reader?
- Once the “on” button is pressed how long will display stay on?
- Why do some Smart Sensors fit very tight in the drilled holes?
- My Reader is tight fitting into the Smart Sensor and difficult to turn the required 45 degrees. What can I do?
- Does my Reader need to be calibrated periodically?
- We had some water spill into one of our Sensors, is it ruined?
- Why do I see “ER”(error) on the Reader display?
- My orange cap was missing when I went to take a reading. Do I need to have the cap on to insure equilibration?
- What's the difference between the Rapid RH and a concrete moisture meter?
- What does it mean when my reader says “hi”?
- Who is qualified to measure relative humidity using the Rapid RH?
- Is it necessary to use both calcium chloride testing and relative humidity testing just to be on the 'safe side'?
- How can I learn more about concrete drying and measuring moisture in concrete?
Rapid RH
| Q: What is Relative Humidity in concrete? |
| A: Relative Humidity is the actual amount of moisture in air compared to the amount of moisture that the air could hold if saturated, expressed as a percentage. In concrete, you measure the relative humidity of a small volume of air at the bottom of a hole drilled into the concrete. |
| Q: What are acceptable levels of relative humidity? |
| A: The type of flooring product to be installed determines the acceptable level of relative humidity. Different RH specifications apply to different materials such as resilient flooring, wood, or epoxy coatings. Check with the floor covering manufacturer for a relative humidity specification. Many flooring manufacturers and industry associations recognize and specify relative humidity testing. ASTM F710 gives general industry guidelines. Typical relative humidity requirements range from 75 to 90%RH, depending on the flooring product. |
| Q: How many relative humidity tests should I use on each job? |
| A: For the Flooring Contractor and as part of the project documentation process, ASTM F2170-02 requires that 3 probes be placed in the first 1,000 sq. ft. and one probe be placed every 1,000 sq. ft. thereafter. If you’re using the Rapid RH™ as a monitoring tool early in a project to determine when final acceptance testing should be performed, several Rapid RH™ Smart Sensors can be placed throughout the floor 28 days after the pour and readings taken as often as desired. |
| Q: What is the correlation between Relative Humidity percentage and Moisture Vapor Emission Rate (lb/1000 sq ft/24 hr) measured with calcium chloride testing? |
| A: There is no correlation between the tests. Relative humidity testing is a measure of moisture condition in the concrete. When a floor covering is placed on top of a slab, it restricts evaporation from the top surface of the slab; moisture within the slab then distributes itself to achieve an equilibrium due to temperature and chemical interactions from the top to the bottom of the slab. In the long run, adhesive and flooring are then exposed to the equilibrium moisture condition at the top of the slab. The calcium chloride kit artificially pulls moisture out of the top few centimeters of the slab and does not reflect the long-term moisture situation that will be established by equilibration. Rapid RH™ Smart Sensors measure the relative humidity that will exist well after the floor is covered. |
| Q: When talking about moisture testing, what does equilibration mean? |
| A: Equilibration or stability occurs when a drilled hole achieves thermal and moisture equilibrium. For the accuracy of the readings it is necessary to wait until equilibrium is restored after drilling. With the Rapid RH™ testing system, equilibrium is achieved within 1 to 2 hours after drilling the hole and the Smart Sensor is inserted. Once equilibration is achieved future readings can be taken instantly. |
| Q: What are the advantages of Wagner Meters' Rapid RH™ Smart Sensor Technology over other relative humidity instruments? |
| A: RapidRH™ Smart Sensors are installed below the surface of your concrete slab, so there is far less risk of damage to the sensors or interference of normal activity on the floor. Once the Smart Sensors have been placed and equilibrated (approximately 1-2 hours) future readings can be taken immediately without any further equilibration time. The Rapid RH™ testing system significantly improves your ability to monitor drying progress of new and existing concrete slabs without adding substantial cost to the project. The drying progress of a slab can easily be monitored for any period of time by jobsite personnel with minimal training, using the Rapid RH™ Reader. There is no need to have a testing agency return to the jobsite with their instruments to obtain more results. |
| Q: How important is sensor calibration to the accuracy of the readings? |
| A: Sensors must have a current, accurate calibration at the time of use to provide trustworthy results. Rapid RH™ Smart Sensors are supplied with a calibration certificate to prove traceability to the U.S. National Institute of Standards and Technology (NIST). Other brands of reusable moisture probes must be periodically checked or returned to the manufacturer for re-calibration. |
| Q: Can I use the Rapid RH™ even if the HVAC isn’t on? |
| A: ASTM F2170-02 specifies that the floor must be at service conditions, in other words with the building (room) enclosed and the HVAC running. Relative humidity is calculated from temperature, so a big difference between what the slab is when testing, and what it will be “in service” is an important consideration. Relative humidity testing performed 40% below the surface of the concrete is less likely to be affected by the ambient conditions than calcium chloride testing at the surface, which is affected greatly by ambient conditions. |
| Q: How long does the battery last in the Rapid RH™ Reader? |
| A: The Rapid RH Reader should last anywhere from 7,000 to 9,000 on/off cycles. |
| Q: Once the “on” button is pressed how long will display stay on? |
| A:
The display on the Rapid RH™ Reader will toggle between RH (%) and Temperature (F) readings for 6 complete cycles, then turns itself off. Each measurement cycle is displayed for 5 seconds, for a total of 30 seconds on time.
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| Q: Why do some Smart Sensors fit very tight in the drilled holes? |
| A: This situation is most likely caused by one of two reasons: RapidRH™ Smart Sensors are placed in holes drilled with a carbide-tipped drill bit that falls within the specifications for an ANSI standard ¾” bit. This range is from 0.775” to 0.787”. The first reason could be that your drill bit has “worn” down with use and has lost some of its “diameter”. This will most likely become noticeable after about 60-70 holes drilled. The other reason could be that you have purchased a new drill bit that is on the lower end of the tolerance spectrum for diameter. |
| Q: My Reader is tight fitting into the Smart Sensor and difficult to turn the required 45 degrees. What can I do? |
| A: In a few instances, even if you have a properly dimensioned drill bit, the Smart Sensor housing may have been deformed when inserted into the concrete. This is especially true if one does not use the proper insertion tool. Use the Insertion Tool that came with the RapidRH Kit or the Rapid RH™ Sensor/Reader Pack to re-form the Smart Sensor housing by inserting the tool and pressing down to re-shape the Smart Sensor housing. This method works quite well to re-form the Smart Sensor housing to the appropriate dimensions. |
| Q: Does my Reader need to be calibrated periodically? |
| A: No. Each Rapid RH™ Smart Sensor has an embedded calibration from the factory. The Reader simply displays what the Smart Sensor tells it. That is what makes the Rapid RH™ Smart Sensor and Reader an intelligent system. Any Reader will display the correct value from any Smart Sensor. |
| Q: We had some water spill into one of our Sensors, is it ruined? |
| A: It is very likely that the Sensor will continue to function properly after water is removed from inside the Smart Sensor housing, for example, by vacuuming. However, if water ran down into the drilled hole around the Smart Sensor housing, then the concrete in that area may be damp; drill a new hole and install a new Smart Sensor to assure accurate and useful results. |
| Q: Why do I see “ER”(error) on the Reader display? |
| A: Check to be sure that there is no debris in the bottom of the Smart Sensor housing before you insert the Rapid RH™ Reader. Each Smart Sensor comes with a serial number label that is packaged inside the Smart Sensor. Be sure to remove this label from the inside of the Smart Sensor. Next, be sure that you line up the white serial number strip on the Smart Sensor with the white serial number strip on the Rapid RH™ Reader, twist 45 degrees clockwise and press the "ON" button. If you still see “ER”, please call Wagner Meters for support. |
| Q: My orange cap was missing when I went to take a reading. Do I need to have the cap on to insure equilibration? |
| A: No. Each Smart Sensor isolates the measuring environment from the outside air using a 3-stage redundancy isolation ring system. As the Smart Sensor is “seated” within the hole, the first stage is a vertical ring on the lowest portion of the Smart Sensor that seals the bottom angle of the drilled hole. At right angles to that, the second stage ring seals off the sidewall of the concrete hole just above the first stage. As a third stage backup, there is a third ring that also performs a seal against the sidewall of the concrete approximately one half inch above the second stage ring. Always replace a missing cap to protect the Smart Sensor and avoid debris getting into the housing when installed on a jobsite. |
| Q: What's the difference between the Rapid RH and a concrete moisture meter? |
A: ASTM F 710, Standard Practice for Preparing Concrete Floors to Receive Resilient Flooring says “All concrete slabs shall be tested for moisture regardless of age or grade level” However, moisture meters should never be used to make the final determination as to whether or not a concrete slab is dry enough for a flooring installation. Here’s why:
No ‘moisture meter’ of any type can give consistently accurate ‘moisture’ readings across the different mixes and densities of concrete. Additionally, other components (metal reinforcing bar, aggregate size and amount, etc.) can cause false indications of ‘moisture’ especially with non-pin meters. But pin-type ‘moisture’ meters are also not practical for moisture measurement because variable chemical and physical characteristics in concrete can cause false readings due to changes in electrical resistance that have nothing to do with moisture.
Additionally, even IF the so-called ‘concrete moisture meters’ were sufficiently accurate (again, they are not), they only measure ‘moisture’ (not relative humidity) in a very small area near the surface of the concrete slab. This type of surface ‘moisture’ testing tells us nothing about the conditions down in the slab. Once a floor covering is placed on a concrete slab, the relative humidity (RH) within the slab will equilibrate throughout the thickness of the slab. This means that a slab that may have been “dry” (low RH) at the surface (without a floor covering) will see a higher RH (migrated from down in the concrete) at the surface, when the floor covering has been installed. This is where the problems occur. The calcium chloride test method (F 1869, Standard Test Method for Measuring Moisture Vapor Emission Rate (MVER) of Concrete Subfloor Using Anhydrous Calcium Chloride), has the same problem, it is just a surface test.
Keep in mind that an uncovered concrete slab will indeed have a relative humidity gradient (typically drier at the surface; much wetter at depth) throughout its thickness until a floor covering is put on top. Under normal conditions, the RH at roughly 50% slab depth will be significantly higher than the surface unless the slab has been down for a long time, and a vapor retarder is directly underneath the slab. In reality, the surface of the concrete will more closely reflect the RH in the room or building which gives no indication of the potential for a flooring failure due to the high RH deep in the slab that will migrate to the surface when the concrete can no longer emit water vapor due to the non-permeable floor covering.
Again, most major floor covering and adhesive manufacturers in North America and Europe already have concrete relative humidity specifications (using ASTM F 2170, Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using In-Situ Probes) in their installation guidelines.
At best, moisture meters (pin-type or surface-type) may have some practicality as relative (qualitative, not quantitative) measurement devices for possibly indicating best placement for accurate, quantitative relative humidity sensors within the concrete. Moisture meters, similar to other non-quantitative test methods, are not final determination tools. |
| Q: What does it mean when my reader says “hi”? |
| A: Since the Reader can only display two digits, "Hi" simply means that the sensor is reading a number of 100. The relative humidity reading would be 100% or the temperature is 100 degrees or more. |
| Q: Who is qualified to measure relative humidity using the Rapid RH? |
| A: Anyone who follows ASTM F 2170 “Standard Test Method for Determine Relative Humidity in Concrete Floor Slabs Using in-situ Probes. |
| Q: Is it necessary to use both calcium chloride testing and relative humidity testing just to be on the 'safe side'? |
| A: Not at all. Howard Kanare, Senior Principal Scientist at the CTLGroup Labs, author of the definitive text on Moisture in Concrete, experienced concrete forensic specialist and industry-acknowledged expert on flooring failures states, “There are many reasons why calcium chloride moisture emission testing cannot do what a Relative Humidity test can accomplish. The bottom line is that RH testing is a far better predictor of whether or not a floor covering or coating on a concrete slab will succeed or fail. It is unnecessary to perform moisture emission tests in addition to Relative Humidity". |
| Q: How can I learn more about concrete drying and measuring moisture in concrete? |
A: The following are excellent resources:
Books and articles by Howard Kanare, Senior Principal Scientist, CTLGroup:
Concrete Floors and Moisture 2nd edition, Portland Cement Association, 164pp, 2008.
Available from PCA online bookstore: www.cement.org/bookstore
“Slabs on Grade: Concrete Floor Moisture Tests,” Concrete Construction Magazine, Sept. 2007.
“Why Are We Still Having Problems with Concrete Floors and Moisture?” Concrete Construction Magazine, 2007 Special Floors Issue, December 2007.
Other Publications
“302.2R-06: Guide for Concrete Slabs that Receive Moisture-Sensitive Flooring Materials”, Reported by ACI Committee 302, American Concrete Institute
“Moisture Testing of Concrete Slabs”, written by Peter Craig and George Donnelly, Sept. 2006 issue of Concrete International, Vol 28, No. 9
“Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes”, Designation: F2170-02, ASTM International
“Concrete Moisture Meters and Calcium Chloride Test: There are Better Ways to Test Concrete for Moisture, written by Christopher Capobianco, Oct. 2007 issue of Floor Covering Installer Magazine. |
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