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)

Keep in Touch:

PHONE: (800) 227-2105

            (503) 257-8957

FAX:      (503) 256-3844

WEB:

www.lignomatusa.com

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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.