Moisture Vapour Emission, Relative Humidity and Testing of Concrete

Image depicts a wet substrate that didnt allow the membrane to cure and
resulted in a damaged,  delaminated membrane.

Materials used in tile and stone installation applications can be affected by moisture during the installation and curing phases. Some materials, such as waterproofing membranes, may not cure properly or may delaminate from a continually wet substrate, or a substrate with a high moisture vapour emission rate (MVER). A substrate which is damp or has a high MVER may also contribute to the formation of efflorescence. Concrete with a high moisture vapour emission rate may also have an impact on a tile or stone installation.

There are generally three quantative tests that are used to determine moisture content in concrete and one qualitative test to show that moisture is present.

1. Calcium Chloride (ASTM F1869 - Standard Test Method for Measuring Moisture Vapour Emission Rate of Concrete Subfloors using Anhydrous Calcium Chloride). 

The Calcium Chloride test involves placing a Petri dish of calcium chloride (covered by a plastic dome adhered to the concrete) on the concrete and allowing the Petri dish to remain in place between 60-72 hours. The calcium chloride absorbs any moisture capour that transmits through the concrete within the plastic dome. The results of a calcium chloride test measures the amount of moisture absorbed and results are stated in pounds per 92.9 m2 in a 24-hour period. Please note that the ASTM F1860 test should only be conducted in interior conditions when the building is completely enclosed and the air conditioning or heating system is turned on, unless otherwise instructed by the test kit manufacturer. This is not a rest recommended for exterior use. 

2. Relative Humidity ( ASTM F2170 – Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs using In-situ Probes)

The Relative Humidity (RH) test involves placing probes in the concrete and taking readings with a hygrometer. A relative humidity reading of 75% or below is acceptable for most tile applications. Please note that the ASTM F1860 test should only be conducted  in interior conditions when the building is completely enclosed and the air conditioning or heating system is turned on, unless otherwise instructed by the probe manufacturer. This test is not recommended for exterior use. 

To continue reading Technical Data Sheet TDS-1166 click here. 

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