Advice for making/laying screed

xmfclick

I am about to repair a concrete terrace which forms the flat roof of a garage and I need to calculate how much plasticiser to buy for adding to the water when making the screed. So, basically, I need to work out how much water I will need to use for the screed. The volume of screed is 2 cubic metres.

I've searched the Net but not found anything that I can understand. The nearest thing I got was an Indian forum where people were talking about the density of sand and cement and percentage of water in the sand and then did some complicated calculation. Can anybody give me a rule-of-thumb idea of how much water I'll need?

Also, what sand/cement ratio would people suggest, and therefore how much sand and how much cement will I need? I've seen anything between 2:1 and 4:1 mentioned, and that the volume of sand is equal to the volume of screed.

Thanks in anticipation ...


Further info: The terrace is in a very exposed location and will see big temperature changes between summer and winter. In winter it will see frost cycles, which have led to the breakup of the existing screed, which is why I also intend to apply a polymeric waterproofing layer. The plasticiser is recommended by the manufacturer of the waterproofing system.

Kiran

Check the literature for your particular plasticiser but it is approximately 300ml/50kg of cement. Given your exposure etc. get something with reinforcing fibers in.

You can probably take the hassle out of it and order the screed ready mixed, it would be a part load but 2m cubed is in the region of 1T of cement and 3T of sand which is quite a lot to mix by hand.