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How to screed a floor

Date posted: 15 January 2015

Although a screed can prove expensive and is not essential because it provides no structural benefit, a screeded floor will usually offer a much better finish than the original concrete floor beneath. Certainly where suspended precast concrete flooring systems have been installed – which is increasingly the case over solid concrete slabs – you can eliminate their significant camber with a screed, preventing potential floor-laying problems.

Generally this is a skilled job carried out by plasterers whilst they are working on walls and ceilings, but some DIY enthusiasts would rather undertake the job themselves – so here we take a look at some of the basics of screeding a floor for beginners...

Get some help

If you are attempting to screed a floor yourself, it is well worth asking a friend to help you. The task demands that you mix the cement screed before levelling the floor, so even if you hire a cement mixer you will still need an additional pair of hands to prepare and transport the cement screed to wherever it is needed whilst you are busy levelling it using a straight edge and a margin trowel.

Ideal screed coat thickness

You should aim for a screed coat of approximately 5 - 7.5cm thick, although you can adjust this thickness to suit your requirements – but always ensure it is thicker than 2.5 cm.

Screeding materials

Self-levelling screed is widely available from DIY shops, but alternatively if you want to save a bit of money you can make up your own using a semi-dry mix of one part cement with three parts sharp sand (Grade A). This material will provide a relatively strong, smooth and level floor on which to lay your carpet, laminate, wood or other floor finish.

The ideal screed mix is fairly dry – almost a powdery texture in comparison to brick and render mortars. If you are mixing it yourself in a cement mixer this will require a dedicated worker – shovelling in sand and cement, then delivering the mix to the screeder(s). Check there are no lumps remaining before you use it. On most sites in a professional context ready-mixed screeds are used instead for added ease (but also at extra expense) – as these are delivered ready made by lorry at the start of the working day. The ready-mixed variety incorporate additional retardants to delay the mix from setting, which means a single morning load can be used throughout the day.

Screeding methods

Check any pipes and cables that are going to be buried in the screed layer because this is your last chance to fix any potential problems.

Easiest option:

There are various means of screeding a floor, but perhaps the most straightforward means of screeding a concrete floor is to use 2×2 wooden screeds (or 3×3 / 4×4 if you require a thicker layer).

  • Lay the screeds on the concrete floor with gaps of about 3 inches and check they are perfectly aligned using a spirit level.
  • Secure them in place with screws.
  • Pour cement screed mix between the wooden boards.
  • Level the screed with a straight edge.
  • Pull the straight edge firmly along the screeds.

Traditional method:

The traditional method of screeding a floor involves:

  • Cleaning the floor thoroughly with a brush to remove dust and any other residues, then sprinkling it with water to help the screed bond with the concrete flooring.
  • Draw guidance lines around the walls of your room, ensuring they are highly visible. Use a water level (or laser level) to set the marks around the room's corners. Join up these guidance marks using a caulk line. It is vital to mark the maximum level of the cement screed on the walls in order to achieve a professional finish – so these lines should be 100% level along the walls of the room, marking the top edge of the screed layer.
  • Start pouring the semi-dry screed along the walls of your room, using a margin trowel to spread it. If it is too wet it will be impossible to work with it. Use a large aluminium straight edge to level the screed along the walls of the room, holding it firmly and moving it to and fro to level the surface.
  • Fill in the rest of the surface of the floor with cement.
  • To finish, you can use a polyurethane float for best results, using circular movements across the entire surface and sprinkling with a little bit of water if necessary.

And finally...

Once you have poured the screed you must make sure you give it adequate time to dry out. Do not walk on the screed for a couple of days. Before laying the final floor covering, expert advice is to allow one day of drying for every millimetre depth of screed. This means that 70 days will be the standard drying time recommended – although if you have installed underfloor heating buried within the screed you can speed up the process a little by placing the heating on at its lowest setting after the first month, then turning it up by three degrees each day until you reach the desired temperature.

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