If you're extending a terrace in Halliwell or fitting underfloor heating in a new build in Horwich, you'll have to decide between a traditional dry screed and a liquid wet screed. Both work well, but they suit different jobs, and the wrong choice can add weeks to your timescale or leave you with cracked tiles. This guide covers the practical differences so you can ask your screeder the right questions.
Around Bolton, "dry screed" usually means traditional sand and cement mixed semi-dry, roughly one part cement to three or four parts sharp sand. It goes down with a shovel and gets levelled and compacted by hand using a straight edge and trowel. "Wet screed" means liquid or flowing screed, usually calcium sulphate (anhydrite) based. It arrives ready mixed and is pumped into the room, where it finds its own level.
Some people also use "dry screed" for dry board systems, such as gypsum fibre boards laid over insulation. Those are handy on upper floors with timber joists, but most ground floor extensions and underfloor heating jobs come down to sand and cement versus liquid.
The biggest practical differences are thickness and drying time. Over underfloor heating pipes, a sand and cement screed normally needs to be around 65mm to 75mm thick. A liquid screed can often go down at 40mm to 50mm, which helps when you're matching an existing floor level in an older house.
Drying is where most projects slip. The usual rule of thumb is about a day per millimetre for the first 40mm and slower after that, whichever type you choose. Anhydrite screed can usually be force dried with the underfloor heating from around seven days, following a gradual warm up schedule. Sand and cement also needs its heating commissioned gently, and it's normally left longer before heat goes on. Bolton's damp, cool weather slows both, so good ventilation and some patience really matter between October and March.
Liquid screed has a real edge with wet underfloor heating. It flows around the pipes with no air pockets and is thinner, so the floor warms up faster and responds better to the thermostat. That is why many new build and extension projects across Bolton, Westhoughton and Farnworth now use it.
The pipes do need to be properly clipped down, and the insulation and membrane have to be taped and sealed, otherwise the pipes can float or the screed can leak into the insulation. Sand and cement still works well with underfloor heating. It's just slower to respond and adds more weight.
Liquid screed needs a mixer lorry or pump parked reasonably close to the property, with a hose run through to the room. On narrow terraced streets in Daubhill or Great Lever that's usually possible, but it's worth talking through. Sand and cement can be mixed on the drive or in a back yard and barrowed through, which suits awkward access.
Prices depend on area, depth, access and the time of year. As a rough guide, both types often fall somewhere between £18 and £35 per square metre for typical domestic work. Liquid screed has fixed costs for delivery and pumping, so on very small areas, say a single downstairs toilet or a floor under 20 square metres, sand and cement often works out cheaper. On larger open plan extensions, liquid screed usually wins on speed and labour.
For a large kitchen extension with underfloor heating and tiles or LVT on top, liquid screed is often the sensible choice. For a small room, a floor that needs building up in stages, awkward access or a tight budget on a small area, traditional sand and cement is hard to beat.
Whatever you pick, check your finished floor height, your floor covering and your timescale with your screeder before work starts. A quick site visit usually settles the question.
Liquid screed can usually take light foot traffic after 24 to 48 hours, and sand and cement after about a day or two. Full drying before laying floor coverings takes much longer, often several weeks depending on depth and ventilation.
Only once it's dry, the laitance has been sanded off and it's been primed. Cement based adhesives react with anhydrite if you skip the primer, so check that your tiler knows which screed has been laid.
Often, yes, particularly where you need to keep the floor thin to match existing levels. The base must be solid, sealed and properly prepared, so suspended timber floors usually need a different approach.