Screed - how much sand/cement?

[myxiplx]

I have a rather wobbly concrete floor which needs levelling before I lay reclaimed parquet on it.

It's too deep for floor levelling compound, so the plan was to lay a concrete screed. I've around 20sqm to cover with 40mm of screed at the deepest points, I reckon just over half a cubic meter in total.

Does anyone know how I can work out how much sand/cement to buy for this (I'm assuming a 3:1 ratio)?

many thanks,

Ross

 

[IanDB]

If it's approx 20sq m and 40mm deep then you're going to need approx 0.8m3 of sand. 3:1 sounds a bit high, I would have gone for 4:1 but it's going to be there or there abouts. You'll need about 7 bags of cement with that quantity of sand.

You need to make sure the concrete base is not too porous - pour some water on it to see how quickly it soaks in. If it soaks away quite rapidly it's worth sealing with some PVA solution.

 

[shaggy]

It's 40mm at the deepest point so I would use pva anyway to bond to the sub-floor. When you go less than 40mm the screed can lift as it dries.