How to ensure a good topping (cement screed)?

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To establish the quantity of sand and cement you would require for a topping of 30mm thick, apply the following equations:

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A. m² of floor x 0,04 = cubic meters of sand required

B. 1(one) Cubic meter sand = 18 wheelbarrows of sand (filled level)

C. Therefore 18÷2 = 9 bags cement required per cubic meter of sand

D. One(1) wheelbarrow = 2 pockets of cement

Mixing the topping (cement screed)
 

• On a clean dry slab, thoroughly mix 2 wheelbarrows filled level with coarse Malmesbury sand (or similar in your area) to 1 pocket of 42.5N cement
  (4:1 mix), until a uniform colour is produced, i.e. (4 wheelbarrows of sand to 1 wheelbarrow of cement) as one wheelbarrow of cement = 2 x 50kg pockets of cement.

• To produce a granolithic topping (cement screed):-

3  Wheelbarrows of Sand

1  Wheelbarrow of Crusher Dust(6mm Stone):

1 Wheelbarrow of Cement (4:1 mix by volume, not weight)

That is: 4:1
1½ Wheelbarrow Sand
½ Wheelbarrow Crusher dust(6mm Stone)
1 pocket cement
 

• Make as many of these dry mixes as would be required to complete floor or area to be covered

• Add water by fine spraying it on with a hose pipe whilst mixing, until the required stiff consistency is produced

• A good test will be to take some screed (topping) in one hand, close the hand with some pressure, open your hand and all the screed (topping) should be intact, but not soggy or wet nor sticking to your hand

• If the screed (topping) is too wet, bubbles will form when finishing a Colour Screed Floor, which will make the finishing process very difficult and tedious.

• If the screed (topping) is too dry, bonding of the Colour Screed Powder to the topping is reduced, which could result in the delamination of the Colour Screed from the topping, causing hollow spot areas and also the screed (topping) will be of an inferior quality due to the lack of water, which will prevent the chemical process of binding and hardening taking place.