Explain briefly, the following methods of construction used for lay screed finishes. – NABTEB QUESTION

(i) Monolithic method.
(ii) Separate

ANSWER

(i) Monolithic method:- This involves laying the screed within three hours of cast-in-situ concrete slab. The mix is prepared in the proportion of 1:1:2 by weight of cement fine aggregate or sand and coarse aggregate. The amount of water is just enough to obtain a workability that enhances full compaction. The screed thickness ranges from 12mm to 40mm depending on the slab and purpose of which the floor is prepared.

(ii) Separate method:- This is the application of the screed to a concrete slab that is cast, set, and hardened before the screed is laid on top to finish the floor. In this case, the proportion of mix is similar to the monolithic type of screeding but the procedure for casting is done in bays of not exceeding 15m². Again, in separate methods of screeding, caution has to be taken as the slab is to be thoroughly cleaned, laitance and scum removed, the slab also has to be hacked and finally wet with water before the screed is laid.