Replacing the Flooring? Test Your Slab for Moisture



Before you install new flooring, you need to test the moisture in your concrete slab. Here's why.

If you're replacing your flooring over an existing concrete slab, you may not have considered it necessary to complete concrete moisture testing. After all, your previous floor didn't fail, nor did it show any signs of moisture-related problems. Why should you test for excess moisture in your concrete when there's no evidence of it?

The truth is, the condition of your previous floor isn't a reliable indicator of how your new floor will react to your slab. Moreover, while you may feel confident proceeding with flooring installation after inspecting your slab's surface, without a pre-installation moisture test by a certified flooring inspector, you may find yourself removing the new flooring, as well, if it's not compatible with the slab beneath it.

Old Slab = Dry Concrete, Right?  

The short answer is: No.

Concrete slabs poured before the 1950s may not have a vapor retarder installed beneath them. Slabs laid as recently as 2001 may have vapor retarders sitting beneath a layer of granular fill which serves as a source of moisture which may migrate into your concrete. A missing, inefficient, or deteriorated vapor retarder beneath an existing concrete slab can all lead to excess moisture seeking a path to the surface where, eventually, it will come in contact with your newly installed flooring.

Other Sources of Concrete Moisture

When your old floor was installed, the surface of your slab was sealed, triggering the remaining moisture's even disbursement throughout the slab as it could no longer evaporate off. Once the slab is unsealed, and a path to evaporation is once again available, a path for moisture to migrate into the slab is also made available. Before sealing it again with a new flooring system, concrete moisture tests need to be performed to ensure the slab is compatible with the products and materials you'll use.

Many old slabs sit beneath floors which were installed with standards and materials that are no longer used in the manufacturing of flooring products. Some formulations are no longer produced due to increased environmental safety standards, while others may have been replaced with more application-specific materials. The moisture tolerance of these older methods and formulas may have been higher than that of your new flooring, and additional moisture mitigation steps may be necessary to bring moisture levels down to meet the standards of your modern flooring application.

Inside and Beneath Your Concrete Slab   

While some sources of moisture, such as leaks from appliances or condensation seeping through cracks, may be evident, other sources cannot be seen or detected on the surface.  

Observations made on the slab's surface don't reveal what's happening out of sight, inside and underneath the foundation. An eroded or absent vapor retarder, for example, may contribute to future moisture-related problems. Additionally, the moisture distribution of an unsealed concrete slab is not consistent. Moisture levels increase as you move further from the surface, and internal moisture tests are necessary to detect these.

Concrete Moisture Testing and Inspections

Concrete Moisture Testing methods exist to provide you with a complete picture of the moisture levels within your concrete which can both help to determine if moisture mitigation is necessary and guide decisions about flooring materials, adhesives, and sealants. While the temptation to use do-it-yourself products may reveal itself, this is not a do-it-yourself job. With so many options for concrete moisture testing, only a certified concrete moisture testing professional with training and experience in the most up-to-date testing standards and protocols should be trusted with inspecting, testing, and interpreting the results.

ASTM f1869 Calcium Chloride Test

The Calcium Chloride Test (ASTM F1869) tests the surface conditions of the slab, which can help to make necessary decisions about when to install your flooring and whether additional mitigation or the application of chemical sealants are needed. In conjunction with other tests, the Calcium Chloride Test helps to create a complete picture of your slab's condition.

ASTM F2170 Relative Humidity (RH) Testing

Surface moisture levels and internal moisture levels are different, with higher levels at the bottom of your slab. RH testing uses in situ probes to measure moisture levels below the surface, helping to project the moisture conditions that will exist after the slab is sealed.  

ASTM F710 pH Testing

Concrete's basic pH is 13, but the pH levels of exposed concrete surfaces are lowered when carbonation (a reaction resulting from the interaction between carbon dioxide in the atmosphere and alkalis in the concrete) occurs.

In addition to the exacting specifications provided by flooring manufacturers regarding concrete moisture levels, they also provide guidance on the necessary pH levels that must exist in the slab for a successful installation. An excess of moisture in concrete can cause changes in the concrete's pH, including the pH at the surface, which can have adverse effects on adhesives, sealants, and coatings which contribute to cosmetic issues as well as flooring failures.

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Sub-slab Conditions Inspection

If the existence, quality, or location of a vapor retarder is unknown, an inspection of the sub-slab through a process known as coring can determine where the vapor retarder is, or if it exists at all. Without a vapor retarder beneath the slab, or if the vapor retarder has eroded or been otherwise compromised, there is nothing keeping ground moisture from migrating into the concrete and traveling to the slab's surface, negatively impacting any flooring installed above it.

Armed with the necessary information about conditions at the base of the slab, you can make the necessary decisions about mitigation, sealants, or the need for additional barriers at the slab's surface to prevent moisture-related problems.  

What to Expect After Your Test  

In addition to the results of your concrete moisture tests, a certified flooring inspector should provide you with recommendations based on your test results which are informed by their knowledge and industry experience. Should you find that the conditions in your slab require mitigation, you can trust that the unbiased advice from a third-party expert will focus on the best solutions for your situation without the agendas that may be present when seeking the advice of a manufacturer or retailer.

To speak with a certified concrete testing professional in your area, call IFTI at 800-490-3657 to schedule a consultation or get advice about your concrete moisture concerns.  

IFTI Staff

Written by IFTI Staff