Why Drill at 40% Depth for RH Testing

Watch and learn With Jason Spangler from Wagner Meters


Behind the ASTM’s 40% Depth Measurement Requirement.

Let’s take a look at why drilling 40% into the concrete slab is so important and where that information came from.
on occasion I’ll get phone calls people ask me how important is it really for me to drill to 40% depth of that concrete slab and what I usually direct them to usually is this graph that we have on our website that represents the information that the scientist Gordan Hedenblad came up with in the late 90’s to adequately show and emphasize how and why that depth is so critical.

Download The Graph

If you look at the graph, it shows vertically how far into the slab we are looking at and horizontally what the relative humidity situation was for that concrete slab. If we look at the red line, what it shows is when the concrete is poured it’s at a very consistent 100% humidity from top to bottom of the slab. And what he really wanted us to look at is, when the slab was not covered with a floor covering or coating, at what depth in that slab would you get a reading that would allow you to  predict what the surface conditions would be like once you actually installed the flooring. so if you look at this yellow line, the yellow line shows the drying curve. the drying being drier at the top and wetter at the bottom. And as you can see, the spot in the middle is where that curve intersects what the concrete moisture situation is once the flooring is installed. The green line shows that because once the flooring is installed instead of having this consistent curve dryer on the top wetter on the bottom, that moisture now has to redistribute because you’ve cut the concrete’s ability to breathe with the ambient conditions in the room. So at the end of the day this is really where it comes from and this shows graphically why that 40% depth is so critical. hit me up at twitter @rapidrhrep if this helped you out or helped you understand proper depth and how critical it is to hit that 40%

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Last updated on December 2nd, 2020

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