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Floor coverings less than 3mm thick are frequently specified to be laid directly onto cement:sand screeds. However, when viewed in cross light, undulations that are unacceptable can often be seen. Special treatment to the surface of the screed may be needed to produce a more acceptable result.
Where very thin floor coverings are to be used the surface finish of the underlying screed must be of a very high quality. Some blemishes in the screed surface are inevitable and thin coverings will only accentuate these defects. Power grinding and/or self-levelling and self-smoothing screeds can overcome the difficulties and it would be prudent to include for the additional requirements at the outset.
Cracks can be filled with suitable sealant but if live, perhaps due to under floor heating, movement joints should be specified which coincide with joints in the flooring.
The Concrete Society document Advice 15 Thin floor coverings on cement:sand screeds provides some guidance.
Acknowledgement: Concrete Society
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