Screed mix guide
Screed Mix Ratios: Sand and Cement vs Liquid Screed
The screed mix decides how a floor is laid, how it is finished and how it behaves afterwards. Here is how a traditional sand and cement ratio compares with a factory-batched liquid screed.
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Short answer: a traditional sand and cement screed mix is typically 4:1 or 5:1 — four or five parts sharp sand to one part cement — mixed with only enough water to bind it. A liquid screed is different: the mix is batched to a set design rather than measured out on site, and it flows into place instead of being compacted by hand.
The ratio matters because it controls strength, workability and shrinkage. Too much cement and the screed is harder to work and more prone to cracking as it shrinks; too little and the surface can be weak and dusty. Too much water is the most common mistake of all — it makes a semi-dry mix easier to spread but leaves a weaker, slower-drying floor.
This guide explains what each part of a screed mix does, how the ratio is chosen, and when a factory liquid screed is the better route. For a side-by-side of the two floor types as a whole, see our liquid screed vs sand and cement comparison.
Typical screed mixes at a glance
| Mix | How it is made and laid |
|---|---|
| Sand and cement 4:1 | Four parts sharp sand to one part cement, semi-dry, laid in bays and compacted by hand |
| Sand and cement 5:1 | Five parts sharp sand to one part cement, semi-dry, ratio adjusted to depth and loading |
| Cement-based liquid screed | Factory-batched mix delivered ready to pump; flows and self-levels |
| Anhydrite (calcium sulphate) liquid screed | Factory-batched gypsum-based mix; suited to dry internal floors |
What each part of a sand and cement mix does
Sharp sand is the bulk of the screed. It gives the floor its body and keeps shrinkage under control, which is why a screed is mostly sand rather than mostly cement. Cement is the binder: it hydrates and hardens, locking the sand together. Water is what lets that reaction happen — and in a semi-dry screed the aim is just enough to bind, so that a squeezed handful holds its shape without water running out.
Polypropylene fibres are often added to help control shrinkage cracking, alongside bay joints set at doorways and changes of depth, where stress naturally concentrates.
Sand and cement screed
- Hand-laid and compacted finish
- Falls can be formed towards drains
- Placement where pump access is limited
How the ratio is chosen
There is no single correct ratio for every floor. The 4:1 or 5:1 range covers most domestic semi-dry work, and the ratio is adjusted to the depth of the screed and the loading the floor will carry. A thin bonded screed and a deep floating screed over insulation ask different things of the mix, and so does a domestic room compared with a floor taking heavier use.
Depth matters as much as ratio. A sand and cement screed bonded to a sound slab typically starts from 25mm, while an unbonded or floating screed over insulation typically starts from 50mm. Bonded work under 40mm usually goes down over a primer or SBR slurry so the new screed grips the base.
How a semi-dry mix goes from ratio to finished floor
- 1
Batch consistently
The same ratio and the same water content batch after batch, so the whole floor cures evenly.
- 2
Prepare the base
Priming or an SBR slurry for bonded work, or a DPM and separating layer for floating work.
- 3
Place and compact
The mix is laid bay by bay and compacted as it goes so no voids are left behind.
- 4
Trowel to finish
Hand float or power trowel to a dense surface ready for coverings once dry.
- 5
Cure and protect
Kept protected while it cures, then checked before tiling or other coverings start.
Site-mixed ratio or factory liquid screed?
Sand and cement ratio mix suits
- Falls formed towards a drain
- Wet rooms, shower areas and balconies
- External thresholds and steps
- Deep fills built up in layers
- Sites where the mix must be barrowed in
Factory liquid screed suits
- Large flat internal floors
- Underfloor heating needing full pipe encapsulation
- Open-plan areas where bay joints are unwanted
- Programmes that need the floor dry sooner
- A consistent mix without site batching
Why liquid screed does not use a site ratio
With a liquid screed the mix design is set before it reaches site, so there is no sand-to-cement ratio for the installer to measure out. The screed is pumped in, finds its own level and wraps around underfloor heating pipes without air gaps — something a hand-compacted semi-dry mix cannot fully match, because it leaves small voids around pipes.
The trade-off is that a flowing screed cannot hold a fall, and gypsum-based mixes are not designed for sustained wet areas. That is why many projects use both: liquid screed for the main floors and a hand-laid sand and cement mix where a fall or a wet-area base is needed.
Screed mix mistakes to avoid
- Adding extra water to make a semi-dry mix easier to spread
- Changing the ratio between batches on the same floor
- Laying a thin bonded screed without priming or a bonding slurry
- Leaving out bay joints at doorways and changes of depth
- Using a gypsum-based liquid screed in a wet room
Drying and the mix
A sand and cement screed dries slowly. The rule of thumb we give customers is roughly a day of drying for every millimetre of depth once past the first 50mm, so a 65mm floor is usually ready for coverings in around six to eight weeks, with ventilation and site conditions moving that either way. A wetter-than-needed mix only adds to that wait, which is another reason to keep water to the minimum that binds.
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Related services
- Sand and cement screed
- Residential liquid screed
- Cemfloor cement-based screed
- Underfloor heating screed
Covering Devon, Somerset and West Dorset
Frequently asked
Not sure which screed mix your floor needs?
Tell us the room, the depth and the floor covering planned, and we will say whether a hand-laid sand and cement screed or a liquid screed suits better. Call 07791 510849.