Concrete Moisture Tests

This graph indicates the results we made with several different brands of relative humidity probes, all meeting ASTM F2170. On the vertical left-hand axis of the graph, we see the percentage of the final reading with the probe. That is you put probes into the concrete, and it took so many minutes or hours for them to eventually come to a final reading. We did this over the course of up to three days. This vertical axis shows the percentage of that final reading. Across the bottom, the graph is logarithmic. It shows a scale in time: 10 minutes, 20 minutes, 30 minutes, 40 minutes, 1 hour, and so on up to 72 hours.

All of the probes, by the time we got out to around 4 hours or so were all reading 95% of their final value. So the relative humidity technique as a method can get you very close to the final answer within a few hours. Clearly, by 24 hours, all the different brands of probes were reading essentially the same and there was no change over the next three days. So that what we found is relative humidity probes can give us roughly the final answer in a very short period of time. They equilibrate clearly within a day.

Now, currently the ASTM F2170 procedure does require the test be reported at 72 hours, but you can make a decision based on getting a quick answer. What we have found, for example, is that if you put the probe in and it reads 95% humidity in the first 15, 20 minutes, it doesn't come back down. It only goes up and it will be going up higher. The opposite is also true. If the probe goes down and you get an answer below your decision point, let's say you're looking for a decision around 80% humidity. If you put the probe in and after an hour it's gone down to 70%, you can have confidence that it's not going to come back up again. We don't see the probes going up and down in results. They simply tend towards the final answer.

So, if it's past your decision point and you know the floor is wet because it's going up, you've got your answer very quickly and you can make your decision as to what to do with the floor at that point. Keep in mind, though, that ASTM F2170 standard still requires official reporting after 72 hours of reading.