Dealing with Concrete Moisture28 Sep 2021, Posted by Concrete Facts in
When concrete slabs, old and new, have moisture issues, it can be a serious problem in all kinds of construction projects. Bubbling, blistering, and blushing are all possible, especially for concrete that is being set for indoor use. However, just like finding the right concrete forms for sale, finding ways to address moisture in concrete doesn’t have to be difficult. While moisture problems are more commonly found in porous, indoor applications, general strategies can be applied to all use cases. The key is to identify the problem and its cause, then begin remediation.
Finding the Problem
The root cause of moisture problems in concrete can often be traced back to when the concrete was produced. In the early 2000s, many building code regulations specified the use of vapor barriers being placed beneath concrete slabs, making them less susceptible to moisture.
The conditions surrounding a slab can also be informative. A wetter slab can often be attributed to the way the roof, gutter, or downspout to a landscape drainage system was built. When the water from the roof goes directly into a storm drain and away from the foundation, it protects concrete from extra moisture.
Waiting Out the Water
Anyone who works with concrete knows that allowing the slab to cure for the full amount of time needed is critical. If you do not allow this curing process to happen fully, water of convenience (the fluid in the cement mix for ease of placement and finishing) can remain present. Concrete acts as a hard sponge and any moisture that rises from the substrate will be absorbed, rising through the concrete slab and filling all its pores and capillaries.
One of the most critical ways to manage these problems is to test for moisture in your slab prior to applying any coatings. Options like ASTM F2170 testing remediate moisture in concrete calls by drilling holes into the new slab, then placing in-situ probes at a rate of 3 per the first 1000 square feet, and then 1 per additional 1000 square feet.
Although ASTM has a standard waiting period of 72 hours to use sensors, you can get a good preliminary estimate with a reading after one hour. This can usually show you within about 5 percentage points of the moisture reading you will end up with at the end of the longer period. With these results, you can begin to discuss your early indications and begin preliminary planning of the next steps. This does not mean you’ll make firm installation decisions. These tests take just a few minutes and can give you important results for future decision-making.
Some people prefer a non-invasive method of testing that does not leave holes open in the concrete. They prefer testing measures that use a pass/fail methodology, measuring moisture levels in 20 to 30 parts of the slab and gaining immediate results based on whether the site conditions and test results line up.
One approach is also to use both testing methods together. The earlier you can identify problems, the earlier you can seal off the slab as needed.
Solutions to Moisture Problems
In newer slabs, moisture can often mean that the slab is not yet rid of its water of convenience, a problem easily solved by waiting one more day for curing to complete. However, this can hold up projects and may not always be a viable option. You can mitigate many of these issues by mechanically profiling a slab’s surface, which opens the pores and allows for quicker release of excess moisture.
Another simple solution is to use an epoxy coating, which acts to seal in the moisture. This can be helpful anywhere there is fresh moisture, including fresh concrete, when moisture is known, or when the state of the surface is unknown and it is a preventative measure.
The best solution is always one that prevents the problem from developing at all, saving steps and cost in the long run. A moisture vapor carrier can be put down early in various strengths, as long as it is not over the moisture threshold as detailed by the manufacturer.
Moisture does not have to be a major problem if you understand the root causes and ways to mitigate these factors. By controlling for moisture, you can save time and costs that free up resources for other important elements of a job.