Newsletter: How to use a Reference Scale for Evaluating Concrete

 

May 2017,

Issue No. 20

Lignomat Product Video

Lignomat in situ probe method for ASTM F2170

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Lignomat Ligno-Scanner SDM

(Watch Video)

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How to Use a Reference Scale When Analyzing a Concrete Slab

When placing a floor covering over concrete slabs a contractor must first evaluate the concrete to ensure proper acclimation has been met. We often use two different methods for evaluating moisture in materials a qualitative analysis and a quantitative analysis.

Qualitative vs Quantitative analysis. Often times with a moisture meter we describe the scale as a qualitative number or a quantitative number. A qualitative number is often referred to when using a reference scale. A reference scale commonly has a range from 0-100 and should be used in terms of more moisture or less moisture. We always tell our customers that this scale should only be used as a comparative reading. Thus one should take a reading in an area where there are no moisture problems and compare that reading to an unknown area where there could be a leak or more moisture. 

Another good application is when a floor installer is preparing to drill holes so he can set his RH probes to do moisture tests using ASTM F2170. The floor installer wants to set the RH probes so that he can get a good representation of the concrete slab. He uses the Ligno DuoTec BW in pinless mode, on setting 25, and starts scanning the floor. His average reading is between 35 and 45, however he has found a few spots that are reading a little higher in the 55 range. Since the floor installer wants to make sure the flooring he is installing stays as beautiful as the day he puts it in, he drills the holes where the moisture meter was reading 55. The meter has picked up more moisture in these areas however the number 55 is only a qualitative number it is not a percentage of moisture. The floor installer drills the holes and sets his sensor. 72 hours later he is ready to take some RH readings. He is getting readings that range from 65% -70%. This is a quantitative measurement taken using a RH% scale. From this we can analyze if the concrete slab is ready to have a floor covering installed. Using the manufactures specifications he can ensure that the concrete slab is ready for his floor covering. 

Floor installer taking a measurement on setting 25 in order to get a qualitative analysis of the concrete slab. Notice there is no unit of measurement on the reading.

The moisture in a slab sits 40% into the concrete slab. Only when a floor covering is placed on top of the slab will the moisture move to the surface and cause floor covering failure. Lignomat pinless moisture meters read up to 3/4″ into material, thus the information that you get from a pinless reading cannot alone determine if a concrete slab is ready for a floor covering. It is always recommended to use the ASTM F2170 test method for evaluating a concrete slab. 

www.lignomat.com  —  Email: sales@lignomat.com – 800-227-2105  —

Lignomat’s Unique Design for Taking Measurements Using ASTM F-2170

The RH BluePeg uses a single microchip, factory calibrated to NIST Standards. Each BluePeg comes with a NIST traceable certificate. The RH BluePeg probes comply with the latest ASTM F2170.

For the first year, Lignomat offers to check the probe calibration at no charge. For sensitive tests, the calibration of the removable probes could be checked after the test. We also sell a salt solution for the RH BluePeg probe which can be purchased for $49.00. The salt solution allows for easy calibration that can be done in-house over and over again.

Good Seal, Easier to Place Sleeves

Lignomat’s sleeves have feathered fins along their entire length, which provide an excellent seal. The lip of the sleeve covers the area around the concrete hole and provides another barrier for any air escaping. At the bottom of the sleeve is a movable cylinder, which places the RH probe every time as required by the ASTM F2170. Standard sleeves require no cutting. 3″ long sleeves are available. We also have top extenders that can be used when measuring gyp-crete.

Better Sealing, Flatter Caps

 Lignomat’s caps come with an o-ring to absolutely seal the sleeves. The caps are flat and do not interfere with any traffic around the test area. We supply red caps to easily spot the sleeve with a RH BluePeg sensor.

Fast Connection

A fail-proof, easy-connect 35 mm stereo plug is used to connect RH probes. No twisting, turning or setting-up an instrument for readings. No pin arrangements need to be fitted.

Most Accurate Testing

Our meter instantly shows the RH and temperature values. The resolution on Lignomat’s meter is 0.1%. No guessing or rounding up.

 

 

Newsletter: How to Make Sure Your Moisture Meter is Working Correctly

 

November 2016,

Issue No. 19

Interesting Websites

Calibration of Handheld Moisture Meters. 9 Wood:

(read more)

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How to make sure your moisture meter is working correctly.

Every floor installer and inspector should have a meter to check the moisture in wood floors. Having a moisture meter and knowing how to use it is not all there is to know. It is also important to know how to check calibration and function of the meter to avoid false measurements.

Floor installers should measure the moisture content upon delivery, before and after acclimation and when the floor has been installed.

Recently I had a phone call from a customer asking me, why two meters he is using on the same floor read differently. He said one meter consistently reads around 6%, whereas the other meter from a different manufacturer read consistently no values lower than 8%. We finally figured out the reason for the discrepancy by checking the default readings for both meters. (Default reading is the value a meter indicates, when the read button is depressed with nothing connected and pins pointing into the air.)

The default reading for one meter was 6% the other meter read 8% even though the pins were not touching any wood. A moisture meter will never read any lower than the default reading, which means the meter with the 8% default reading will never be able to indicate any moisture content below 8%, even when measuring drier wood.

Since the moisture meter user may not be aware of any malfunctioning of the meter, it is advisable to check the basic functions of a pin and pinless meter before and after each test series. In addition, the calibration of moisture meters can be checked with calibration test blocks available from the moisture meter manufacturers.  These external check blocks are essential for a valid check procedure. Moisture meters often have internal calibration checks, but those checks do usually not include the connection to the measuring plates for pinless meters or the connection to the pins, cables or hand probes for pin meters.

Basic function check for pin meters:

When the on-off switch or read button is depressed by hand without touching the pins, the lowest moisture value for the chosen wood species setting should be displayed (default reading). This test indicates there is no short within the circuitry. Meters may also show higher values if the area between the 2 pins is contaminated or has condensation.

This meter from Lignomat shows the lowest value (default reading for wood group setting #3) with the decimal point blinking. On-off switch between the pins is depressed, but fingers are not touching the pins.

When the on-off switch or read button is depressed and both pins (integral pins on the meter or pins of the external probe) are touched at the same time with two fingers, at least 12% should be indicated. Continuity test indicates that the connection from pins to circuit board to display is working.

Calibration check:

Last, the calibration can be checked with the pin test block. The pin check block consists of one or two resistors which produce a certain moisture value when pins are touching the contact points of the calibration check block. 

Only an external check block can confirm, that probe, cable and meter are functioning properly. Measurements are supposed to be within +/-1% of 12% for this calibration check block.

Basic function check for pinless meters.

When the on-off switch or read button is depressed and nothing is touching the measuring plates on the back of the meter, the lowest moisture value for the chosen wood group is displayed (default reading).

Hold meter in the air to make sure no material is touching the measuring plates and the lowest possible value appears on the screen with “Min”. 

For the continuity test, place the pinless meter on your forearm and depress the read key, a high moisture value should be indicated. An additional meter check can be performed by measuring a realm of paper. If the paper test is done repeatedly with the same setting, the indicated value should not vary significantly over the course of a year. This can be used to check consistency and accuracy of the calibration over time.

 Last, the calibration can be confirmed with the calibration check block. The check block for pinless meter is usually a material plate which produces a defined reading when the meter is lightly pressed against the surface.

Always press down slightly on the meter when taking measurements and when checking the calibration with a calibration test block. 

After checking the meter with the above described methods, you think you are ready to take measurements. Stop. A very important next step is to set the meter for the correct wood species. Find out about the wood species.  Find out if it is an engineered floor and what the hardwood species of the top layer is, set the dual-depth meter for that species and the ¼” measuring depth. Now you are ready to start a test series.

Last, your moisture measuring report should include place, date, moisture meter brand and instrument name, pin or pinless, wood species setting and measuring depth, location where the reading was taken and indicated moisture value in percent. A photo of the meter while taking readings is always helpful.

What if all of the above has been followed, but accidently the wrong species setting has been used for the measurements. If you cannot go back to take the readings again, ask the meter manufacturer, if they can tell you what the readings would have been with the correct setting.

www.lignomat.com  —  Email: sales@lignomat.com – 800-227-2105  — Grete Heimerdinger

Product Manager at Lignomat.

 

Newsletter: Storing and Acclimating Your Lumber

 

August 2016,

Issue No. 18

AT A GLANCE

*Storing and Acclimateing Your Lumber

* Moisture in Concrete: Free and Bound Moisture

Interesting Websites

Concrete Floors and Moisture

(read more)

Scientific article about different methods to measure moisture in concrete. Great information about the different types of water in concrete.

(read more)

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Storing and Acclimating Your Lumber

Many woodworkers end up collecting and storing all different types of wood whether its leftovers from a previous project , or wood for a project that will be happening down the road. It usually ends up in an old shed or the side of the workshop and of course preferably in a climate controlled room. Where ever you may be storing wood it is important to understand how the climate the wood is in affects the usability of the wood.

 

If dry wood is stored in a damp place the wood will pick up moisture and expand until equilibrium with the surrounding air has been reached. If the wood is stored in a dry area the wood will lose moisture and shrink until equilibrium has been reached. For corresponding values check the EMC chart.

 

Proper acclimation of your wood before starting a project will minimize moisture problems when the woodwork is done and brought into the home. Nothing is more frustrating than making a nice dresser and bringing it into the home only to have it shrink and cause loose joints. An easy recommendation that we always provide our customers is to take a moisture meter and measure a table or some other woodwork in the home. Once you have established what the wood has acclimated to in the home then you have a MC% of what you want your wood that you are working with to be.

Moisture in Concrete, Free vs Bound Moisture

Water in concrete is presented in three states: as free water held by capillarity, as absorbed water held by surfaces forces and as bound water held chemically. The ideal method of moisture measurement should quantify amounts of these three states but this is a difficult task because moisture in concrete is not uniformly distributed, and moisture distribution varies with the exposure time (Li Chunqiu 2008). Temperature, wind speed and environmental relative humidity are variables that must be considered at the moment of this measurement as well.

 

Using a pin moisture meter or a pinless moisture meter Is not a good method for analyzing moisture in a concrete slab. These types of meters are not able to pick up the different types of water in concrete. The meter will measure all of the water in the slab not just the free water.

The free water is what is going to affect the vapor emissions that will cause floor covering failure.

 

Measuring the moisture of a concrete floor is very hard because of the nature of concrete. The floor covering industry is always evolving and trying to incorporate a more accurate and efficient method for evaluating moisture in a concrete slab. 10 years ago people were only doing the calcium chloride test when analyzing moisture in concrete. Today many manufactures and people in the floor covering industry have moved to using the RH in-situ probe method following ASTM F2170 standards. Lignomat has developed a system for measuring concrete following the ASTM F2170 guidelines. Please call if you are interested in purchasing. If you would like a more detailed video of how the system works please visit link below.

 

https://youtu.be/UnyRz6XFTqs

Li Chunqiu, L. K. ( 2008). “Numerical analysis of moisture influential depht in concrete during drying wetting cycles.” Tshingua Science and Technology Vol 13, N°5: 696-701.

 

Newsletter March 2016: Case Study Floor Covering Failure

 

March 2016,

Issue No. 17

AT A GLANCE

*Case Study: Customer Calls with Floor Covering Failure

* Why is Wood Cupping and Shrinking?

Interesting Websites

Popular Woodworking Magazine: Moisture Meters

(see more)

Understanding, Preventing, Detecting and Correcting Moisture in Concrete Floors

(read more)

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Case Study: Customer

Calls with Floor Covering

Failure

We recently had a customer call us with a problem. He was called onto a site where the floor had cupped and boards were twisted. He wrote us that he inspected a wood floor, ¾ x 5 inch, stapled down, upstairs over plywood.  Consumer told him the species was Teak.  The ¼ and ¾ depth readings were done with a SDMspecies setting 55. 

While writing the report, he called and found out from the floor reatiler that the species was Timbauba.  The product name for the consumer was Golden Teak.  So he do not know how to adjust the meter readings.  

Location            1/4″ depth        3/4″ depth           

     

Hall                        12.4                12.4                    

Hall                       10.9               11.1          

Bedroom front      10.1                10.4              

Front closet          11.9               12.3               

Hall bedroom        11.1               11.3               

Master                   10.2               10.7               

Shelf                      12.8              12.8            

Shelf                      11.4              11.6

Pieces of wood sent in by customer to be evaluated. The wood as shown above was warped. 

Grete Heimerdinger’s response – VP Lignomat

here is a web-site which has information about Timbauba http://www.fpl.fs.fed.us/documnts/TechSheets/Chudnoff/TropAmerican/htmlDocs_tropamerican/Enterolobiumschomburgkii.html

The specific gravity for Timbauba is very different from 55, that is why those measurements came out so different. The low Lignometer K readings indicate that the meter was giving default readings, which means the resistance in the wood is so high , that the meter cannot measure the wood.

The SDM readings were corrected for setting number 55. To see the difference in readings between 55 and 84, I took a piece of White Oak and measured the moisture on setting number 55. The readings were about 11.1, 11.0.Then I changed the settings to number 84 and took readings again of the same White Oak piece in the same location and the measurements showed 6.9 and 7.0. Changing the setting from 55 to 84 will reduce the measured values by about 4%. I hope this information helps. Let me know, if you have any more questions.

 Grete 

When taking measurements of a piece of wood it is crucial to have the proper calibration for the species of wood to be tested.

When using a pinless moisture meter the specific gravity is the calibration factor. With Lignomat pinless moisture meters you simply put the specific gravity into the meter. For example: Specific Gravity of Timbauba is 0.84 so the Ligno-Scanner moisture meter should be set to 84.

The calibration for a pin type moisture meter is a little more complicated. Lignomat performs an oven dry test to find the appropriate calibration for the wood. When you have a moisture meter with 2 wood group settings all woods are put into those two settings depending on the oven dry results. When you have a moisture meter such as the Lignometer K which has 150 different wood groups there is a much finer calibration so you will get a more accurate reading depending on the wood species.

Lignomat offers free oven dry testing for any wood that we have not tested in the past.

For this case study we did not have a setting for Timbauba so the inspector was asked to send in a few pieces of wood no more than 6″ long so that we could establish the proper Lignometer K setting for his wood. 

After the oven test the results were as follows:

Warped piece of wood measured 8%

Unwarped piece measured 8.7%

This obviously shows that the readings that were taken with the wrong settings were inaccurate. After the oven dry test is done a calibration for the moisture meter is established. 

Nobody needs to wonder why the warped wood tested with such normal moisture contents. Lets assume the wood floor was delivered, not tested, and installed at a higher moisture content than 6-9%. As the wood dried out, it warped and then when tested it showed the right low MC.

Make sure to give Lignomat a call if you are having problems finding the correct wood species settings. We can help.

800-227-2105

sales@lignomat.com

Why is Wood Shrinking and Cupping?

Wood movement occurs, when the moisture in wood changes. Then, floors are cupping, table tops delaminating, veneer is checking and boards are warping.
No shrinking and warping will occur, when an equilibrium with the surrounding air has been reached, which means wood is not losing or absorbing any moisture. 
The EMC chart below lists stable wood moisture 
values between 2.3% and 24.3% for ambient conditions of 10-95% RH at temperatures of 30-1000F. According to the chart, wood at 10.1% will not shrink or warp, if the relative humidity remains at 55%.
Besides listing stable conditions, the EMC chart 
allows predictions and explanations:
For instance, if dry wood with a moisture content 
of 6% is exposed to 55% relative humidity at 700F, 
the wood will pick up moisture until 10.1% has been reached. Wood species, coating and exposure time determine how much moisture will actually be absorbed. However, at 55% relative humidity, wood 
can never pick up more moisture than 10.1%. 
An all important pair of tools: Hygrometer and wood moisture meter
No more surprises!
Measure and compare wood moisture and relative humidity with the EMC chart to predict, if wood is stable or will loose or gain moisture.