For those not working in the construction industry and to the untrained eye, it may be difficult to both understand and / or recognise the difference between concrete and floor screeds.
Something that is very odd given that both materials are made from the same basic ingredients; cement, aggregates and water.
The basic chemistry is the same for both concrete and screed – the cement and water forms a paste and coats the surface of the sand or the aggregates, and the cement paste hardens by a process called hydration, forming a hardened mass of high strength and durability.
However, the size of aggregates used is different, the grade of the cement used is different, the mix consistency and finish is different – because both materials intended use is very different!
Concrete has a much coarser mixture than screed, consisting of larger, hard-core aggregates, which are the key element that gives it its durability and makes it strong and long lasting.
Because concrete has the potential to hit very high strengths, it is used across the construction industry for structural purposes – including floor slabs. It is the most used man-made material in the world.
Screed however is a smoother mix, which consists of considerably less aggregates to that of the mix used for concrete.
Screed is usually applied on top of the concrete slab and is most commonly used as a finishing layer on internal floors or to level the floor prior to final floor coverings carpet, tiles, natural stone, linoleum, wood flooring, resin coatings etc.
Screeds are required when a colourful or functional floor is needed rather than a bare concrete surface. For industrial purposes, or commercial locations, which will undergo frequent traffic, a more robust screed is required than is used in DIY or residential projects.
Most screeds are used for internal purposes only, often covering heating systems, acoustic or thermal insulation. Polymer-modified screeds can be installed in external locations, as they are hardwearing, water resistant and able to withstand a more rigorous environment.
Traditionally screeds are sand and cement mixtures, blended and applied on site. However these are often unpredictable as the ratios and properties cannot be exactly determined and so can lead to a weak flooring layer liable to crack, peel or collapse without warning.
To counter this unreliability there are a number of proprietary screeds and kits available on the market offering enhanced strength and a faster application speed that will react more predictably.