8. Concrete - General

8.1 Concrete dries at a rate of around one month per 25mm of slab. So a 100mm slab takes around 4 months to dry out. On a 6 month programme with a 200mm slab, the moisture content is likely to be an issue if there is a lot of wet weather that reduces the hydration of the moisture from the concrete; and possibly even where the roof is installed early and the slab retains a cool environment that similarly reduces hydration.

8.2 The issue with painting cementitious substrates (concrete/render) that “looks dry” without testing the actual moisture content is that the addition of finishes such as vinyl/paint will seal the concrete and change the internal equilibrium of the concrete moisture – meaning the moisture deep in the wall will migrate towards the “observed” dry substrate and then the surface that was thought to be “dry” will become excessively moist and cause Delamination of the finishes.

8.3 Many applied finishes to concrete – vinyl, carpet, waterproof membranes, sealers all require a maximum moisture content of the concrete to ensure that the adhesives used in the installation work correctly.

8.4 The moisture content is tested by an Electrical resistance and impedance test (using a moisture meter).

8.5 The CCAA document below provides a comprehensive review of moisture in concrete, how to test it, other considerations

8.6 http://www.ccaa.com.au/publications/pdf/Moisture.pdf