There are times when a concrete slab will appear to be dry but still have too much moisture under your finished flooring. That’s why we want to use moisture testing. By performing a moisture test you can gain knowledge about what’s going on at the top of the slab and within the slab.
Whether that’s testing for in-situ relative humidity, moisture vapor coming off of the top of the slab or even just checking the surface of the concrete. Once you have these numbers it can help guide you if the slab is dry enough to install your flooring or if it needs to dry out some more or require a moisture mitigation system.
Why Do We Want to Know If There’s Moisture In Our Concrete?
As mentioned above concrete is porous. When concrete is poured there is a certain amount of moisture that goes into the slab. It can also get moisture from below the slab if there are leaks or moisture getting through the ground.
We want to know how much moisture is in our concrete because many of the coatings, adhesives and wood flooring will only allow so much moisture. If the flooring that you want to install requires the concrete to be drier than it currently is you can experience issues with bubbling, adhesive failing, flooring lifting and discoloration.
We talked about this more in The Critical Role of Moisture Mitigation in Concrete Floor Installation. Knowing if your concrete is dry enough before you install can save the flooring contractor from having to tear up their newly installed flooring.
Types of Moisture Testing on Concrete
There are many types of testing you can do to find out how moist your concrete is. Here are a few that we perform.
You can do an in-situ relative humidity test, calcium chloride test. There are also moisture meters that can test the concrete non destructively and give you readings of where you may want to dig deeper and test. Testing the PH of the concrete can also be beneficial.
Once you know what flooring you’re trying to install you can see what type of moisture testing they recommend.
What is In-Situ Relative Humidity Testing?
An in-situ relative humidity test can test for moisture within your concrete slab. By making small holes in the concrete and placing a probe at the correct depth we can get an idea of what’s going on under the surface.
The ASTM that goes along with this test is ASTM F2170. The advantage to this test is it’s able to detect moisture below the surface. Your slab may be dry on the surface and still have too much moisture within the slab.
What is Calcium Chloride Testing?
Calcium Chloride testing is another method to use when testing your concrete. It will give you a number of how much moisture is vaporizing from your concrete. Usually the ASTM F1869 is used when performing this test.
This can be helpful to know if the flooring you’re trying to install calls for it. However you are only getting the number for what’s on the surface of your slab. It will not tell you what the in-situ relative humidity is within your concrete. So don’t always assume that it will replace a RH test.
What Can An Impedance Moisture Meter Tell You?
Using an impedance moisture meter can give you an idea of what’s going on throughout your concrete. We use this type of moisture meter to test concrete in a non destructive manner. We can use it to find hot spots in the concrete that may be higher than normal and dig deeper to see if its really an issue.
We don’t always use this moisture meter to test if concrete is dry enough for a flooring system. But again if your flooring requires it we can provide those numbers.
What Makes Concrete Dry Enough To Install Flooring?
There is no one moisture level that your concrete needs to be at in order to install any flooring. The flooring company will let you know how much moisture their flooring can take.
So you’ll want to make sure that your moisture levels are at an acceptable level that your flooring can withstand. That’s what we want to find out by doing these tests on your concrete.
Things That Can Affect Your Concrete Moisture Levels
Age of your concrete, temperature, humidity, leaks and even moisture coming from under your concrete can all affect your moisture levels. If your slab was left to dry out for a long period of time and then HVAC was turned on you may start to see changes in your concrete.
Just because your slab is older doesn’t mean that it’s dry. Vapor barriers can break, dirt can stay wet, leaks and even flooding can all cause concrete moisture issues.
What if My Concrete is Too Moist?
If you receive high numbers when testing your concrete there are options. Depending on the flooring system and how much moisture is in your slab we can discuss options with you.
Allowing more time for the slab to dry out is always an option. Or installing a moisture mitigation system can also be done. Custom Concrete Prep & Polish can apply a moisture mitigation system to your slab if you feel your slab has too much moisture for the flooring that you want to install.
Document Your Concrete Moisture Testing
It’s always a good idea to document your concrete moisture testing. We can show you what the moisture levels are on your concrete and compare them to what the flooring requires.
By analyzing the floor system, moisture levels and the type of flooring we can work together to ensure that there aren’t any surprises down the road. Contact Custom Concrete Prep & Polish to see if your concrete is dry enough to install flooring.
