The adhesion of the levelling screed to the base should be examined by tapping the surface with a rod or a hammer: a hollow sound indicates a lack of adhesion.

Tests to check the adhesion of a levelling screed to its base should be made as late as possible in a construction programme when the maximum effect of drying shrinkage has taken place. Tests undertaken in less than 4 weeks could be unreliable. Account should be taken of the time necessary for any required replacement section of levelling screed to be laid within the construction programme.

Good preparation of the base is essential and, together with good workmanship, will minimize loss of adhesion; however, it cannot be guaranteed that adhesion will always be complete. It would be unrealistic to expect levelling screeds thicker than 40 mm always to completely adhere, even to a correctly prepared base.

If any hollowness is found it is usually confined to the edges and corners of bays and on either side of any cracks that have developed in the levelling screed. Hollowness, indicating lack of adhesion, does not necessarily mean that the screed is unsatisfactory unless it is accompanied by a visible or measurable lifting of the edges of bays or at cracks, to the extent that the lifted areas of the screed could break under anticipated loads. The type of flooring to be applied subsequently and the end use of the floor should also be taken into consideration.

Areas of levelling screed that are considered to be unsatisfactory should be treated by one of the following methods.

a) Making good the affected areas by filling or injecting the hollow areas with a low-viscosity synthetic resin to stabilize and improve the bond between the levelling screed and the base.

b) Isolating the affected areas by sawing, making vertical cuts into adjacent sound screed, and taking care to minimize the effect of the cutting-out operation on the adhesion of the sound screed. The unsatisfactory areas of screed should then be removed and replaced by new material.

Interior Screed Ltd are the UK’s leading floor screeding contractors specialising in all types of floor screeding systems. Established in 2010 and working with many of the biggest and most prestigious names in the residential and commercial building sector’s we install screeds into building developments of all sizes. From complex large-scale commercial projects to residential and mixed-use contracts, we carry a comprehensive range of floor screeding products and services designed to offer our customers a one-stop floor screeding facility.

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