Moisture Mitigation and Moisture Testing

By dciflooringUncategorized

Even if we are not installing your floor-covering, we can handle your moisture issues. We can also perform moisture testing.

Slab Moisture Mitigation: Moisture mitigation is risk mitigation.

Within any facility there are multiple activities taking place, people are hard at work, and most of them are standing, sitting, walking, or working on a floor. While we may not always consider the importance of the floor, imagine trying to operate your business without one. Most flooring will be applied to a concrete slab, whether carpet, resilient, ceramic, wood, or a resinous system. Concrete must have moisture in order to develop and maintain its strength, but excess moisture can create a host of expensive problems in your building, not the least of which is floor covering bond failure. Floor covering bond failures due to slab moisture vapor emissions are estimated to cost over a billion dollars each year. Even if the floor doesn’t fail, there is still an increased risk of mold and mildew growth. So what can we do to avoid having to replace failed systems and shut down businesses in the process? We need to test for moisture and make a business decision.

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Where does moisture come from?

Moisture comes from two principal sources; free water from the concrete mix (about a 25% ratio, by weight, of water to cement is required to hydrate the cement and cause the reaction that turns cement, aggregate and water into concrete) and from the earth beneath the slab.

Why does it come to the surface?

Before a covering is installed on the floor, the slab is trying to achieve equilibrium with the ambient air (if the ambient relative humidity is low then the slab will dry faster than if it is very humid.) After a low or impermeable flooring system is installed, the moisture in the slab will attempt to again achieve equilibrium within itself. Moisture that has settled lower in the slab will migrate towards the surface. As this moisture migrates to the surface of the slab it brings salts from the slab and creates a moist, highly alkaline environment at the interface of the flooring and the slab. This alkaline environment creates a new imbalance with the moisture in the slab and increases the level of migration in order to bring more neutral water from the slab to the area of higher alkalinity causing bond failures.

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What can be done to minimize the problem?

  • Proper water/cement ratios should be a maximum of 0.42-0.5 w/c (water in excess of 0.25-0.28 is considered “water of convenience” and only assists in placement.)
  • The pour should be monitored to prevent additional water from being added during placement.
  • Porous aggregates should be avoided (if lightweight aggregates are needed above grade they should have a low porosity.)
  • Hard troweling should be avoided (this can create a thin densified layer on the surface that inhibits adequate drying.)
  • Curing should be performed using blankets or sheeting for a minimum of 7 days (curing compounds can inhibit adhesive bond to concrete, slow drying, and may need to be mechanically removed prior to installing floor-coverings or resinous systems, adding cost.)
  • Curing compounds do not “wear off” as the concrete cures despite claims of some manufacturers.
  • The slab should be under roof and conditioned as soon as possible

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Testing Methods

Situ Probe Relative Humidity Test (ASTM F-2170)

This is the preferred method. This test uses probes placed in the slab (40% depth for slab on grade or pan, 20% depth for suspended slabs) to give a quantitative reading of the relative humidity (RH) of the slab. This method gives consistent and reliable readings of the relative humidity within the slab which gives you a better picture of what will happen once a floor-covering/resinous system is installed and the slab moisture equalizes. ASTM requires this test to be performed once the slab is in a conditioned environment. Although it will not provide an ASTM certified result, some may choose to place the probes and perform initial testing prior to conditioning to get an idea of slab moisture.

Calcium Chloride (ASTM F-1869)

This method is still specified by many manufacturers, but waning. This test will give a quantitative reading of the moisture vapor emissions at the time that the test is performed. It cannot tell you what the slab moisture content is, so it cannot predict what will happen once a system is installed. There are also frequent false readings with this test; it can be dramatically affected by ambient conditions; and it can be inconvenient in occupied spaces. This test may be used in conjunction with In Situ RH testing. This test must be performed with the slab in a conditioned environment for 48 hours prior to and during the testing process, failure to do so results in a meaningless result.

If it is determined that you have too much moisture, what are y our options?

  • You can wait until the slab dries to an appropriate level (if construction schedules permit, you may be able to wait a period of time and retest, though there is no guarantee of the amount of time it may take to reach the desired level).
  • You can install a moisture mitigation system (there are several quality epoxy based systems for mitigating moisture vapor emissions that can be installed to allow you to stay on schedule; there are also many more systems that are untested and use questionable methods and chemistry).
  • You can roll the dice (you may decide that the cost of mitigating is greater than the risk, inconvenience and cost of having to replace the flooring if there is an issue down the road).
  • Non moisture sensitive flooring options – Polished concrete, ceramic tile and certain resinous systems may be suitable for slabs with higher levels of moisture vapor transmission

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There are a variety of mitigation systems on the market utilizing various prep methods and chemistry. When selecting a system, it is important to understand why you are considering that system: solving your immediate installation problem and insuring against a potential floor-covering failure. Moisture mitigation is risk mitigation and we all want the best chance of success. Epoxy type mitigation systems have consistently demonstrated superior success rates across the board and are recognized as the “right” way to get it done.

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