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.