Ultrasonic measurement of Paint on Manhole

[SewerHog]

I have used a polyurea to coat the interior of our manholes. The thickness is to be 125mils on concrete and 150 on brick. The contractor is saying that his ultrasonic meter will not give a reading over 150mils. And that all his work is over 150mils in thickness. The kit with the meter has test samples but only 20 and 80 mils. Something does not seem right. Maybe the wrong probe! Help...

 

[Ron]

Many ultrasonic thickness gages will not read over 150 mils. Others will. If his gage is limited to 150 mils and your spec is 150 mils, why not use it to its max if you can get a reading (lets say the gage shows 150 but the actual is 155...do you care?). Conversely, if the thickness is less than 150 mils, it should work fine...showing failure of the thickness criteria.

Concrete is a difficult surface on which to measure coating thickness, whether optically or electronically. The most accurate measurements will be done by taking a small plug through the coating into the concrete, then directly measuring the coating under a microscope.

 

[bimr]

Ask the Contactor to get a different meter. DeFelsko makes one that can measure up to 175 mils thickness:

http://www.defelsko.com/applications/masonry/masonry.htm

 

[SewerHog]

Thanks bimr, but DeFelsko no longer make that model. They have in-cooperated it into the model 200 but it has a limit of 150 mils and does not do well with polyurea. So they say.
Thanks...
Any other suggestions!!!

 

[dbaird]

I don't know if this is of any value to you:

http://www.sensorsmag.com/sensors/m...s-measurements-using-laser-triangulation-7050

David Baird

Sr Controls Designer
EET degree.
Journeyman Electrician.