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About

A floor screed is a semi-dry cementitious mixture used to level a concrete subfloor prior to installing tile, wood, or other finish floorings. Unlike structural concrete, screed has a much lower water content (consistency of damp earth) and uses sharp sand (no large aggregates). Getting the quantity right is tricky because the mix compacts significantly.

This calculator determines the precise amount of Ordinary Portland Cement (OPC) and Sharp Sand needed based on your specific mix ratio. Standard industry practice typically suggests a 1:4 cement-to-sand ratio for a strong, reliable bed. This tool is essential for tilers, bathroom fitters, and DIY renovators ensuring their substrate is perfectly flat and durable.

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Formulas

The calculator assumes a compacted dry density of approximately 2,200 kg/m³. The logic sums the total mass required and splits it according to the weight ratio.

V = Area × Thickness

Total mass including 10% waste factor:

Masstotal = V × 2200 × 1.10

Material breakdown based on ratio (e.g., 1:4):

Cement = Masstotal1 + Ratiosand

Reference Data

Mix RatioCement (Parts)Sand (Parts)Typical Application
1 : 313High traffic, heavy-duty bonding
1 : 414Standard domestic floor screed
1 : 515Light duty or thicker non-structural beds
Dry DensityApprox. 2,200 kg/m³Fully compacted state
Coverage~20 kg per m² @ 10mm thicknessGeneral estimation

Frequently Asked Questions

The most common ratio is 1:4 (one part cement to four parts sand). This provides a good balance of strength and workability. For areas requiring higher strength, a 1:3 mix can be used.
You should use 'Sharp Sand' (also known as Grit Sand or Concrete Sand). Do not use soft building sand (used for bricklaying), as it lacks the structural integrity required for flooring and may crack.
For unbonded screeds (separated by a membrane), the minimum is usually 50mm. For bonded screeds (chemically bonded to the concrete base), it can go as thin as 25mm, though 40mm is safer to prevent cracking.
Screed should be a 'semi-dry' mix. When you squeeze a handful, it should clump together like a snowball without water dripping out. If it is too wet, it will shrink and crack; if too dry, it won't compact properly.