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    Concrete & the moisture factor


    Cement, Flooring, In The Press

    In the previous issue of FLOORS in Africa Magazine the focus was on concrete substrates, and the numerous characteristics to look for in respect of their soundness, which may complicate installations. When dealing with cracks, guidelines are established to help identify how to go about resolving the various types encountered.

    Narrow cracks measure less than 0,5mm in width, while medium cracks are between 0,5mm and 1,5mm. Wide cracks measure 1,5mm and more.

    Narrow cracks are normally apparent where shrinkage on the surface has occurred. These are often shallow and do not pose a problem. The surface can be primed with BONDiTe primer and, once dry, LEVELiTe self-levelling compound can be applied next as per specifications. If hollow sounds are evident, scabbling is indicated in order to literally ‘get down to the root’ of the sound substrate. 

    The matter should also be referred to the main contractor who should provide instructions on how to proceed. Medium cracks must be vacuumed to remove dust, and can be chased to widen if deemed necessary. The crack is then primed with BONDiTe and thereafter filled with LEVELiTe and smoothed to the surface level. Lastly, the whole surface is primed and LEVELiTe applied as per specification. Wide cracks are indicative of the slab having fractured straight through to the compacted sub-base. This requires professional input – an engineer or the individual responsible should be approached to obtain further instructions.

    It should be highlighted that the vast majority of resilient flooring failures are attributed to excessive moisture in the substrate. The common factor in all concrete, mortar and screed mixing and chemistry is water. And whatever form it takes, this water translates into moisture. Concrete is porous, and even when the atmosphere is dry, some moisture may be present. As the concrete cures, moisture is then retained. Different floorcoverings have variations in density, composition and surface coatings, all of which cause differing vapour transmission rates, and thus their tolerance levels for substrate moisture will inevitably vary.

    Consequently, the flooring manufacturers’ maximum moisture content for their specific flooring should not be exceeded, especially as South Africa is the ‘melting pot’ of products entering the country from around the world, each with its own unique specifications.


    Floors Magazine: Feature - Cement and concrete

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