Southport Liquid Screed Guide: Types, UFH, Drying Times and Cost

What is liquid screed?

Liquid screed is a self-levelling floor screed mixed to a pourable consistency, pumped onto the prepared floor and left to find its own level. You may also hear it called flowing screed or liquid flow screed. Once it has set and dried, it gives a flat base for the final floor covering.

It is either laid on insulation, where it floats as a separate layer, or placed directly onto a concrete slab. Because the mix travels through a hose, big rooms are covered in a short time and the floor does not need to be anywhere near the pump.

That suits Southport, where floors can be in villas split into flats, older streets with houses opening onto the pavement, or new homes on busy estates. The material is the same in each case; the preparation, access and timing are what change.

Preparing a floor for liquid screed

Most problems with a liquid screed floor start underneath it, so the preparation matters as much as the pour. This is the list we go through with customers before agreeing a date:

• Roof on and windows and doors fitted, or the openings sheeted over
• Insulation boards flat, tight together and fully supported
• Edge strip run round every wall, column and door frame
• Membrane lapped and taped so no screed can escape through the joints
• UFH pipes clipped down, filled with water and pressure tested
• Finished floor height marked on the walls and agreed with the builder
• A clear path from the road to the room for the hose
• Other trades told the room is off limits while the screed sets

Anhydrite or cement-based liquid screed?

Liquid screeds fall into two groups. Anhydrite screed, also known as calcium sulphate screed, has a gypsum-based binder. Cement-based liquid screed, or liquid cement screed, uses cement instead but still flows and levels itself.

Anhydrite is a common pick over underfloor heating because it can generally go down in a thinner layer and passes heat through well. Its weak point is moisture: it is not normally used where the floor will stay wet, and the surface usually needs sanding and priming before certain finishes.

Cement-based versions cope better with damp conditions and tend to need less surface preparation before cement-based adhesives. Which one fits depends on the room, the floor finish, your programme and the manufacturer's advice, and we are happy to talk it through before you book.

Liquid screed for underfloor heating

Underfloor heating and liquid screed are a natural pairing. The mix flows under and around each pipe, so no air gets trapped and the heat has a continuous path up to the floor surface.

There is no single minimum liquid screed thickness for underfloor heating; the product and the heating system set it. As a rough guide, anhydrite screeds in houses are often specified with about 25mm over the top of the pipes, which typically means a total depth of around 40 to 50mm on insulation. Cement-based products generally ask for a little more. The manufacturer's figures are the ones to follow.

A thinner screed means less mass to warm, so the system responds more quickly. Pipes should be filled and pressure tested before the day so any leak shows up while it can still be fixed, and clipped down firmly, because loose pipe can lift as the screed flows around it.

• Pressure test the pipes before the pour
• Clip pipework down so it cannot lift
• Keep the heating off during the pour and the early curing period
• Bring the heating up gently, following the screed manufacturer's commissioning guidance

Liquid screed thickness and depth

How thick the screed needs to be depends on what is underneath and the load the floor will carry. Floating on insulation, anhydrite liquid screeds in houses commonly start at around 35mm, going deeper for heavier loads and commercial floors. Bonded directly to a concrete slab, a thinner layer is usually possible. Cement-based liquid screeds normally need a little more depth than anhydrite.

With underfloor heating, the figure that matters is the cover over the pipes, so add the pipe height to get the total depth. Settle the finished floor level early. In an older Southport house it decides whether doors need trimming and whether there is a step between the new floor and the original rooms.

Liquid screed drying times

Liquid screed is usually firm enough for light foot traffic within a day or two, but firm is not the same as dry. How long it takes to dry enough for flooring depends on the depth, the type of screed, the temperature, the airflow and the season.

For anhydrite liquid screed, a widely used rule of thumb is roughly one day per millimetre for the first 40mm, with drying slowing after that. Keeping air moving through the room helps, and many anhydrite products allow the underfloor heating to be used to force-dry the floor after an initial period, following the manufacturer's schedule. Cement-based liquid screeds vary more between products, so go by the data sheet.

Before any flooring goes down, have the screed moisture tested. Both the screed and the flooring manufacturers set the moisture levels they accept, and fitting timber, laminate or some vinyls too soon is a frequent cause of failed floors.

Liquid screed cost per m2 and per m3

You will find a liquid screed price per m2 quoted online, but on its own it tells you little, because depth, access and the size of the job move it a long way. We price every floor individually rather than publishing a rate. These are the main things that affect the cost:

Screed is supplied by volume, so the cost per m3 and the cost per m2 are tied together by depth. Volume is the floor area multiplied by the depth in metres. A 30 m2 extension at 45mm needs roughly 1.35 m3, and a 100 m2 ground floor at the same depth needs about 4.5 m3. Add 10mm to that larger floor and it needs another full cubic metre.

For a firm figure, send us the approximate area, the depth if you have it, whether there is underfloor heating and a line about access. Photos of the room and the route from the road speed things up.

• Floor area, as bigger floors tend to work out more efficient per m2
• Depth, which sets how many cubic metres are needed
• The type of screed and any particular product the specification calls for
• Underfloor heating, which can change the depth and the product
• How far the hose has to run from the vehicle to the room
• Timing, including fitting around other trades
• Whether the insulation, edge strip and membrane are complete

Liquid screed or traditional screed?

Traditional screed is laid by hand: mixed on site, wheeled in and levelled with a straightedge, so a big floor takes time and the result depends on the person doing it.

Liquid screed is pumped in and levels itself, which makes large areas quick to lay and gives a very flat finish. It is usually thinner, especially over underfloor heating, and it surrounds the pipes completely. The trade-off is that the build-up underneath must be well sealed and the drying period needs proper attention before flooring.

Not sure which suits your Southport floor? Tell us about the room, the finish you want and your timescale, and we will give you an honest view.

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