How to determine the moisture content of concrete

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Discussion Overview

The discussion revolves around methods for determining the moisture content of concrete, particularly in the context of preparing for flooring installation. Participants explore various techniques, including electrical resistance measurements and gravimetric methods, while considering the accuracy and applicability of these approaches.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant suggests using an Ohm meter with probes set 1cm apart to estimate moisture content, seeking a corresponding resistance-to-moisture table.
  • Another participant acknowledges the feasibility of using an Ohm meter but cautions against relying on its quantitative accuracy for structural elements.
  • A participant mentions the specific context of using self-levelling concrete and the requirement for moisture content to be below 5% for adhesive application.
  • There is a recommendation for a Calcium Chloride test as a more reliable method, with a reference to ASTM guidelines.
  • Concerns are raised about the impact of additives in self-levelling concrete on conductivity and the reliability of resistance readings.
  • A participant suggests a qualitative method involving plastic sheeting to check for condensation as an indicator of moisture issues.
  • A later reply introduces the qualitative versus quantitative testing issue and references an article by an industry expert for further insights.
  • Another participant expresses a similar inquiry about measuring moisture through a concrete floor and seeks reviews on the Calcium Chloride test method.

Areas of Agreement / Disagreement

Participants express a range of views on the effectiveness and reliability of different moisture measurement methods, with no consensus on a single best approach. There is acknowledgment of the limitations of certain techniques and the need for caution in interpreting results.

Contextual Notes

Participants note that the accuracy of resistance measurements may be affected by the composition of the concrete, and there are unresolved questions regarding the emission rates of moisture from concrete surfaces.

Who May Find This Useful

This discussion may be useful for individuals involved in construction, flooring installation, or those seeking to understand moisture measurement techniques in concrete applications.

lorand
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Hi there,

I'm just curious as to how to determine the moisture content of some concrete we've recently set. I was hoping I could just use an Ohm meter to, set the probes say 1cm apart and have some kind of table that corresponds to xxx resistance = xxx % moisture content.

Anyone have any ideas?
 
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Yes it is possible to measure the moisture in concrete with such method, as long as you don't consider the results (quantitatively accurate) if you are measuring a structural element such as a slab, beam, ...

If you have the cores of the structural element, you could try a gravimetric approach which is more accurate.
 
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Oh, this is only a small amount of self levelling concrete - in a room about 4m x 3m - and thickness of the self-levelling is ~11mm. Reason we need to figure out the moisture content is we are planning on laying down some bamboo flooring (with adhesive) and the documentation requires less than 5% moisture content for normal sealant application.
 
Electronic meters are usually not recommended to get an accurate reading, as i said above. I will recommend another procedure like Calcium Chloride test, you could look it up on the ASTM website.

However, I'm not sure about the emission rate such concrete sheet might have. I'll have to look into it, but have you tried a reading already?
 
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I wouldn't believe the resistance readings anyway. Self levelling concrete has additives that might affect the conductivity. A good rough check can be made by taping some plastic visqene to the floor and let it sit overnight. ANY condensation on the underside of the plastic will cause problems with adhesion.
 
Sorry to dig up an old thread, but I was browsing this forum and I can't stand to leave this question not completely answered. All the methods that have been talked about here can give an indication, but there's the whole qualitative vs. quantitative test issue. I think this article by industry expert Howard Kanare really addresses the issues more directly than I've seen anywhere else.

http://www.wwwagner.com/pdf/HK%20Problems%20with%20moisture%20Eprint.pdf

Good luck to all who run across this problem again!
 
lorand said:
Hi there,

I'm just curious as to how to determine the moisture content of some concrete we've recently set. I was hoping I could just use an Ohm meter to, set the probes say 1cm apart and have some kind of table that corresponds to xxx resistance = xxx % moisture content.

Anyone have any ideas?

I just joined this forum and it's so weird that I just came across this thread because I have a similar question! I'm interested in finding out how much moisture is going through a concrete floor attached to my house. Does anyone know where I can get a test? I did a little research and discovered a place that has a calcium chloride test but I would like a review if anyone has used it, and also I would like to know how to use it!
Thanks so much!
 

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