You’ve just seen how measuring at the correct depth is critical to the utilization of relative humidity testing in concrete slabs. Again, this information came from studies that were done at Lund University in Sweden back in the mid to late ’90s. It was determined in those studies that in a slab drying from one side 40% and a slab drying from two sides 20%, nonetheless that that was the equivalent depth or the important depth for measuring the relative humidity. So what does that mean?
To review, the relative humidity at that depth, 40% or 20% depending on the slab, that’s what the surface of the slab will be eventually when the slab has had a chance to equilibrate when a floor covering or coating has been placed on top and the moisture vapor can no longer leave. The slab is going to equalize. Let’s just look at a depiction of that for a minute.
Here we see an open slab. We see your typical gradient, drier at the top, increasingly wetter as we go down. We’re depicting the equivalent depth at an RH of 89%. So, we want to measure at that depth, this is a slab drying from one side, and we wish to measure at 40% of depth and what we’re going to see is 89%.
Once the floor covering or coating has been placed on top of that slab, the moisture within that slab is going to equalize throughout the full thickness and we are going to have a higher relative humidity at the surface of the slab. That relative humidity may be at dangerous levels. Right now it’s not, because that slab has not been topped off with any kind of a covering or a coating. But once we do and it has time to equalize, what we now see is pretty close to that equivalent depth reading relative humidity. We’re showing 87% or perhaps even higher, which is very close to that 89 that we showed at 40% of depth.
Again, that could be a dangerous relative humidity level, but this is what happens in a slab. Again, it’s very important that we are measuring only at the equivalent depth and we’re not getting some kind of a watered down reading. Here’s where one of the major advantages of the Rapid RH comes into play.
Let’s look at some other methods that use a sleeve and an external probe to try and measure relative humidity. The Rapid RH system does not use a sleeve, but we’ll get into that in just a minute.
Here’s an example of a sleeve. There is no sensor in this. Again, an external sensor of some type is used to actually read down into the environment that’s created by a sleeve, and there are many different types. Here’s another type of sleeve that will go down in the hole. Here’s another form of sleeve here that you’ll see. They all are inserted into the hole. They’re trying to create an environment for which an external probe of some type will read the relative humidity. But often they cannot read exactly at that very important equivalent depth.
Let’s just look at glaring example of that with this first one that I’ve grabbed here. You’ll see that there are basically horizontal cut-outs along almost the full length of this particular sleeve. That’s a real problem and let’s look at why.
Again, we want it to read at, in this example let’s say we want it to read at this particular depth in the slab because that’s important for getting the correct reading. We can’t do that with this device because we’re reading at different levels in the concrete slab. This is going to give us a low, watered down reading, often significantly low, underestimating the true relative humidity, that true relative humidity at equivalent depth that we need to know about. There’s no way you can get that kind of a reading with this type of sleeve. So that’s a very flawed design.
Let’s take this one for a minute. We have different hole cut-outs, and often, what I’ve seen in the field with this type of device, it’s done incorrectly even by consulting engineering firms, where instead of just knocking out one hole at the correct depth, they will knock out holes along the full length and attempt to get a reading. Again, you’re going to get a watered down, low average, which will underestimate the relative humidity. This could lead to a wrong decision of a floor covering or coating being put down. You put it in there and we’re getting a reading at this depth and maybe that depth. That’s not right because we’re not reading only at the correct depth.
Other sleeve designs have similar problems, and the thicker the slab and the deeper the hole, the more the problem can increase.
Let’s look at the Rapid RH for a minute and why it has a huge advantage over these other methods. The Rapid RH uses what we call a Smart Sensor, and I’ll refer to this as a barrel. Looks kind of like a little miniature barrel, about three-quarter diameter, about an inch and a half long. The sensor, the patented design, the actual sensor is embedded in the bottom side of the barrel.
So when you insert one of the Rapid RH stay in place sensors in a hole, you’re inserting it all the way to the bottom of that hole. No matter what depth you are, this gets inserted to the very bottom. If it’s an inch and three-quarter hole, if it’s a four inch deep hole, it doesn’t matter. You’re only going to read at that depth.
Let’s just show a depiction of this. We’ll insert it here. It’s a very thin piece of concrete. We’re reading at about this level here. Even if we have a deep hole and we take it all the way down, we’re only reading right here. That’s where we want to read. Now, how do we get that reading? Again, the sensor’s here, no power, you don’t have to worry about that.
We get the reading from a reusable device that we call the Reader. It has little pogo pins on the underside, and this allows electrical connection and communication between the Rapid RH Smart Sensor and the Reader. The Reader will display the relative humidity and the temperature that’s being seen by the sensor on the bottom side of this barrel.
Let’s just look down inside. I don’t know if we can see it or not. Down inside the barrel, that’s not where we’re taking the reading, but that’s where the contact takes place. There are four little contact pads between the Smart Sensor barrel and the pogo pins, the metallic pins on the bottom side of the Reader. It’s as simple as, when it’s in the hole, you line it up, put it in, put the Reader in, turn it on, and we get a reading. It’s as easy as that.
Again, the Smart Sensor, unlike any other relative humidity testing methods, the Smart Sensor doesn’t leave the hole. It stays in place.