Question 1

How thick should floor screed be?

Accepted Answer

Traditional sand and cement screed (also known as floor screed or sand-cement screed) should be a minimum of 65mm thick when laid unbonded over insulation, or 50mm when bonded directly to a concrete slab. For underfloor heating systems, 50mm minimum above the pipes is standard — use our Underfloor Heating Coverage Calculator to size your UFH system. Self-levelling screed can be thinner at 25-50mm. Always check Building Regulations Approved Document C for your specific application.

Question 2

What is the correct mix ratio for floor screed?

Accepted Answer

The standard mix for traditional floor screed is 1 part cement to 3-4 parts sharp sand (by volume). A 1:4 mix is most common for general domestic use. For heavier-duty areas like garages, a stronger 1:3 mix is recommended. The sand must be sharp (concreting) sand, not building sand, to achieve the correct strength. This calculator covers traditional, self-levelling and fast-set floor screed mixes used across UK domestic and commercial projects.

Question 3

How long does screed take to dry before tiling?

Accepted Answer

As a general rule, traditional sand and cement screed takes 1 day per mm of thickness to dry sufficiently for tiling — so 65mm screed needs approximately 65 days. Self-levelling/liquid screed dries faster, typically 1 day per 2mm. Fast-set screed can be walked on in hours and tiled within days. Once dry, use our Floor Tile Calculator to work out tile quantities, or our Floor Levelling Calculator if the screed needs a levelling skim before tiling.

Question 4

How much sand do I need per m³ of screed?

Accepted Answer

For a traditional sand-cement screed at any cement:sand ratio between 1:3 and 1:5, you need approximately 1.6 tonnes of sharp sand per m³ of finished screed (using the yield assumption that the cement fills voids in the sand, so mortar volume ≈ sand volume — the standard convention per BS 8204-1 and Hanson published rates). The mix ratio determines the cement quantity, not the sand. A standard bulk bag (tonne bag) of sharp sand typically contains 0.85-0.9 m³. For a typical room (4m × 5m at 65mm depth = 1.30 m³ + 10% wastage = 1.43 m³), you need approximately 2.3 tonnes of sand.

Question 5

Can I screed over underfloor heating pipes?

Accepted Answer

Yes, screeding over underfloor heating (UFH) is standard practice. Use a minimum 50mm screed depth above the top of the pipes for traditional screed, or 25-30mm for self-levelling liquid screed. The underfloor heating must be pressure tested before screeding. Do not turn on the heating for at least 21 days after laying traditional screed. Size your UFH system first using our Underfloor Heating Coverage Calculator.

Screed Calculator — Sand, Cement & Volume for Floor Screeding

How We Calculate This

The formula

UK screed depth guidelines

Frequently Asked Questions

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