The Difference Between Concrete and Screed
Concrete and screed are similar in some respects – after all, they are both made from the same basic materials: cement, water and aggregates (e.g. sand and stone). But, when it comes to their use as building materials, concrete and screed are very different from each other.
To put it simply, concrete is used for construction and structural tasks, while screed is applied on top of a concrete base to provide a smooth, even and long-lasting finish.
Physical differences between concrete and screed
Concrete and screed are relatively easy to tell apart, once you know what to look for. Concrete has a rougher texture than screed because it contains coarse aggregates. As well as sand and cement. These small stones are normally 20mm or less in size, and are easily visible in liquid concrete. Concrete is normally laid much thicker than screed, with a minimum recommended thickness of 100mm for domestic use, and up to double that thickness for areas in which there is heavy footfall – e.g. on driveways.
Screed, on the other hand, is a type of mortar. It is a smooth, soil-like mixture made from cement and fine, sharp sand – without the gravelly aggregate that is found in concrete mixes. The maximum grain size for dry screed is around 4mm. This allows for a more fine-grained appearance compared to concrete in its liquid form. As screed is most commonly used as a finish on internal floors, it is usually 50–100mm thick (on average, about 75mm). Once laid and compressed this becomes smooth.
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Types of concrete and screed
Concrete is available in a wide variety of mixes, which can be tweaked depending on what the concrete is going to be used for. It is always made using cement, water and aggregates, but these materials can be mixed in different ratios to achieve certain qualities. If you need a lightweight concrete, for example, an aggregate like Lytag could be used in the mix. Or, if you want concrete with a particularly high compressive strength, then the water–cement ratio can be adapted on the lorry to increase the cement amount. Some customers might need concrete that is versatile or that sets quickly – with volumetric concrete mixers, these are all qualities that can be achieved.
Like concrete, there are many different types of screed available. These include bonded, unbonded, floating and liquid (or flowing). Bonded screed is applied directly to a concrete base, while unbonded screed is laid onto a water-resistant membrane that sits on top of the concrete. Floating screed is a type of unbonded screed that sits above a layer of insulation, making it a popular option for use with underfloor heating systems.
The benefits of concrete and screed
Concrete has the potential to hit a very high compressive strength, which makes it an ideal building material. It is used in everything from walls, driveways, patios and roads to piling, concrete floors and other building structures. As well as being immensely strong, concrete is durable, economical, long-lasting and versatile. It is also non-combustible, which means that it could be advantageous in the event of a fire. The main benefit of readymix concrete, in particular, is that it can be batched to your exact specifications and amount using volumetric mixers.
Screed is generally used to create a smooth, bump-free finish to a concrete floor or surface. As well as improving a concrete base aesthetically, it can also lengthen its life – the compact mix of sharp sand and cement provides a durable and long-lasting top layer that protects the concrete floor from the impact of constant use and heavy footfall.
Admixtures for concrete and screed
Additives (or admixtures, as they are more commonly known in the trade) are materials that can be added to concrete and screed, either before or during the mixing process, to alter their properties. Admixtures allow for various functions of the concrete or screed, depending on the requirements of an individual job – for example, plasticisers can be added to enhance the workability of the building material. The admixtures can be categorised within their functions to include bonding, shrinkage reduction and damp proofing.
Admixtures can help drastically when laying concrete or screed. They can do a number of different things, such as slowing down or speeding up the setting time of the material. Here at Rapid Readymix, we often add fibres and retarders to our screed products – fibres help to reduce cracking, while retarders enable the material to remain workable for longer.
Professional advice about concrete and screed
If you want to repair, replace or install a new concrete floor in your home or commercial property in London, Surrey or the South East, we can help you identify the right type of concrete and screed for your individual requirements. If you need to undertake significant work in your home or business space, it is generally a good idea to consult a recommended builder before taking action.
We strongly advise using a quality assured readymix concrete supplier that is BSI approved. Rapid Readymix is Britain’s best reviewed BSI Certified concrete supplier and we would be glad to discuss supplying your construction project anywhere in London and the South East.
We are happy to work with your chosen building contractor to deliver your assured concrete and screed efficiently and in line with their agreed building schedule.