When planning a building project’s timelines, inherently, the time allotted for drying concrete seems to be one of the issues that affects many of the finish tradesmen late in the building process. There are a variety of factors that can influence the drying process and slow it down to the point of serious cost and inconvenience to the flooring and general contractor professionals who are waiting on it.
However, the good news is that it is also possible to speed up that process by setting up optimal conditions for allowing the necessary moisture (or water vapor) to leave the concrete slab.
The Right Mix
One of the first places to control the amount of moisture in a concrete slab is in the initial concrete mix. The higher the volume of water added to the concrete, the more will have to be removed through the drying process. Pretty basic, right?
The challenge with reducing water levels too much in the initial mix is that it comes with an increased risk of cracking due to shrinkage in the finished slab. It also actually reduces the natural routes that the moisture vapor uses to exit the slab and so can delay drying time instead of improving it.
Other options like desiccation agents or synthetic aggregate substitutes may help reduce the initial water content, but each comes with its own risks, so it is wise to research the options well. It might be a tradeoff that doesn’t really buy you any time.
The Right Finish
Once concrete is poured, the trowel finish that is applied will also impact drying time. That slick, hard-trowelled finish can actually seal the surface of the concrete by “pinching off” the capillaries necessary to allow moisture to move to the surface and away. A high blade angle, high blade speed or attempting to burnish too quickly can also have the same effect, so don’t rush the trowelling or your drying schedule may pay the price.
The Right Environment
The best way to optimize a drying schedule is to be sure that the ambient environment around the slab is at ideal conditions. These conditions are a combination of ambient air temperature + ambient relative humidity above the slab + air movement + dehumidification equipment.
- Air temperature and ambient relative humidity work together in an inverse relationship to create the optimum conditions for moving moisture out of the slab and into the air. When the temperature rises, the air is capable of holding more moisture (higher humidity levels), so bringing the area to service conditions provides (in most cases) the ideal conditions for letting the slab dry as efficiently as possible.
- Air movement draws the moisture from the surface of the concrete slab in a cycle that allows more moisture to rise from within the slab and be drawn away until it has reached a point of equilibrium with the surrounding air.
- As the moisture is moving into the air and being circulated with air movement, having dehumidification equipment able to extract the moisture out of the air will allow for a continuous drying cycle. Most HVAC systems are simply not adequate to remove the moisture being released by the drying concrete, and if it only circulates in the ambient environment, the concrete will take a very long time to dry to installation specifications.
The right combination of these factors will create ideal drying conditions for concrete applications.
The Right Concrete Moisture Test
Ultimately, the only way to determine if your concrete slab is dried to specifications is to test the moisture content with relative humidity (RH) testing, like the Rapid RH® . Unlike traditional surface-based testing, RH testing goes within the slab to determine accurate moisture content. It’s a proven method for determining accurate levels before proceeding with a flooring application, or choosing the final flooring products based on moisture tolerances.
It can also be useful for determining the choice of applied drying measures based on the current moisture content of the slab and the project schedule. Because the Rapid RH® provides the “final” moisture content of a concrete slab if it were to be sealed (with a sealant or other flooring application) at that point in time, decisions relating to drying conditions and flooring application can be made with a complete and accurate assessment of the concrete slab.
With best conditions in place, and accurate RH testing to verify the process, drying times can be improved for excellent and lasting flooring results.