THE HARD FACTS
Jason Spangler, Wagner Meters’ Sales Manager, looks at how moisture moves through concrete and the effects it can have on floorcoverings.
There's more moisture in concrete than you'd think. Once the slab hardens, it's easy to forget what an active role moisture still plays in its preservation. To protect your flooring, you need to understand where moisture comes from and how it moves through concrete.
The largest source of moisture is the batch water used to mix the concrete. Additionally, if the concrete isn't poured over a vapor retarder, the slab may continuously absorb moisture from the ground. Until the slab is sealed with a finished floor product, it may also absorb moisture out of the air. The slab could also take on any water from external sources, such as leaky pipes or rainwater.
The challenge lies in that concrete needs water – but only the right amount. After the initial pour, we may think we see the concrete ‘drying’ but what’s actually happening initially is the curing process. Curing occurs when the chemical process of hydration begins. What we really see is the concrete hardening and strengthening. Without adequate curing, the concrete won't be as strong as it needs to be.
Significant moisture remains in the slab even when it’s mostly done curing. That's why the slab still needs time to dry. If the floor is sealed before the slab reaches the proper moisture level, flooring failure will likely follow.
WHY MOISTURE MOVES
THROUGH CONCRETE As the concrete cures and dries, air pockets and veins form within it. These are the byways for batch water and vapor to move through the slab. How? It's called ‘capillary action.’
Capillary action is how water from a tree's roots nourishes its branches. It pushes moisture upwards. The same thing happens in concrete. That's why the moisture condition of the slab isn't uniform until it's sealed. As long as water can evaporate from its surface, capillary action will push it upwards.
Unless...the relative humidity (RH) in the air around the slab is higher than the RH within the concrete. When the air holds more moisture than the concrete, the concrete can absorb it. The reverse is also true. If the RH in the concrete is higher than the air's RH, moisture will evaporate from the slab.
EXCESS MOISTURE CAN BE
A PROBLEM Water, so vital for strengthening concrete as it cures, is no friend of flooring. Excess moisture that gets trapped beneath a sealant or other finished floor product can be catastrophic.
36 | SUBFLOOR PREPARATION
As excess vapor struggles up to the surface, it can lead to osmotic blisters in the flooring or sealant. The chemicals it carries might delaminate the floor or prevent the sealant or adhesive from adhering. When the vapor carries up salts from the cement, it can leave a whitish-grey substance on the floor. If wood flooring is installed above the concrete slab, the excess moisture can cause it to crack and buckle.
Excess moisture in concrete can lead to many unsightly or dangerous defects in the floor. Your best defense is knowing the RH within the concrete slab so you don't seal it before the slab has dried sufficiently. The best way to know the slab's RH is by performing an in-situ RH test at the right depth in the concrete slab.
Curing and drying concrete for a durable floor takes time. But you don't want to guess when the excess moisture has left the slab. With an in-situ RH test, you don't have to.
For more information about moisture in concrete and how to conduct an in-situ RH test, call Wagner Meters worldwide toll- free at 844-574-0228 or visit the website.
www.wagnermeters.com.
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