What is the difference between concrete and screed – this is the question many people ask themselves who want to build a foundation, lay a terrace or simply inform themselves about building materials. Confusion often arises because concrete is used for foundations, but screed also comes to the floor.
There is also the term concrete screed. So what is the difference between the two terms or is it the same in the end? This guide is intended to help you
What is the difference between concrete and screed? In short: one is defined by ingredients, the other by the area of application.
What is concrete?
As already explained in the last guide to the question How long does concrete have to harden? concrete consists of granular stone such as gravel or sand, cement (which in turn consists of clay and lime), mixing water and, if necessary, other additives, binders or catalysts. In short, concrete is a moist mixture of rock, clay and lime.
When drying and curing concrete, there are chemical processes that lead to a crystalline bond.
This makes concrete hard and ideal for foundations and as a building material for other applications. There’s even concrete furniture! However, concrete is not the last layer for foundations, especially in the residential property sector, before laminate, tiles, parquet, linoleum, carpet, carpeting or the like can be applied to the floor. Because before the screed is needed…
A screed concrete floor is simply a layer of finer concrete laid on top of a pre-existing and cured concrete base. The screed is usually a simple, cement, aggregate and sand mix but proprietary screed mixes exist for specialist use.
The screed may be applied directly to the underlying concrete or may be applied as a floating finish on a layer of rigid insulation material.
What is screed?
Screed is the covering and straightening layer which is placed on the concrete foundation and levelled off. Screed can consist of similar components to concrete, but there are different types of screed. In other words: concrete is defined by its components; screed is defined by its function.
These types of screed exist:
- Cement screed (CT)
- Mastic asphalt screed (AS)
- Synthetic resin screed (SR)
- Calcium sulphate screed (CA)
- Magnesite screed (MA)
Not all types of screed use water, which is a big difference to concrete. This is because it requires water in order to become the resistant building material that many people appreciate and use.
Why Screed Concrete?
The screed is laid for one of three reasons:
- to improve the appearance of a pre-existing concrete floor. Concrete comes in many forms and conditions. A concrete floor may well be structurally sound but may have superficial damage, stains, roughness or inconsistent colouring. A screed finish will provide an attractive, homogenous and smooth finish. This appearance can be further enhanced after the screed had been laid throught the application of the Becosan System (more on that later).
- to provide an even base for the application of tiles, parquet, linoleum or vinyl.
- To complete the addition of underfloor heating. Underfloor heating systems usually consist of tubes that carry heated water. These tubes are then encased in screed concrete so that they are completely hidden and the screed acts as a conductor of heat.
Types of Screed
The most common type of screed is a simple concrete mix. However, because it is the layer that can be seen we select better quality cement, smaller and more evenly sized aggregate and a fine sand. The screed can be further enhanced by the inclusion of a coloured dye into the mix for example a metal oxide pigment like Bayferrox. Additionally, fibres may be added to the screed mix which will further enhance strength and reduce the risk of the appearance of unsightly cracks in the future. This type of screed will usually cost between 15€ and 20€ for a square metre.
If one is short on time but not so worried about budget it is, of course, possible to buy Pre-Mixed screed like the Ardex A35 Mix. These products provide a reliable consistency of finish and can dry to a state where they can be walked upon in as little as four hours. Slightly more expensive one should budget at around 18€ to 25€ per square metre.
Another type of screed is Anhydrate Screed like Screedflo. This is a liquid that is hosed on to the floor and requires , therefore, less skill to apply. The liquid finds its own level and dries within 48 hours to leave a smooth finish. This type of screed is commonly used with underfloor heating systems. Because of the simplicity of application this screed works out at around 13€ to 18€ per square metre.
Making a screed concrete floor better using the Becosan System.
Once installed a screed concrete floor will be more attractive and harder wearing than a plain concrete floor. However, it is still just concrete and particles of concrete can disaggregate and become dust. Also, the screed can absorb liquid and can stain. Both of these problems can be eliminated through the use of the Becosan System.
The Becosan System begins by micro-grinding the floor opening the pores and eliminating the micro-roughness if the surface. Becosan Densifier is then applied to the floor penetrating into the substrate chemically reacting and binding the free lime and calcium hydroxide in the floor. The result is a harder surface which is resistant to wear and, hence, creates no dust.
After further polishing Becosan Protective Sealer is applied. This makes the screed floor more resistant to liquid spillage which is not absorbed and can be easily mopped up.
A screed concrete floor treated with the Becosan system will last for very many years and will give a surface comparable to any marble floor and at a fraction of the cost.
The individual types of screed explained briefly
In the following, the five types of screed mentioned above will be examined in more detail. This gives you the opportunity to get a more precise picture of screed and make the difference to concrete.
Cement screed is a covering and straightening layer also called CT according to DIN EN 13 813. Cement screed is also called concrete screed, as the ingredients are approximately the same. Sand and cement are used, for example in a mixing ratio of 3:1.
The sand has a grain size of less than 8 mm, in some cases a maximum of 4 mm. Water is also used for mixing the mixture. Just like rapid concrete, there is also a rapid screed subtype for cement screed.
This has various additives which favour or accelerate the hardening process.
Mastic Asphalt Screed
Mastic asphalt screed is also called AS and, contrary to the above example, has nothing to do with water. This type of screed consists of the ingredients bitumen, sand, chippings and stone dust.
The mixture is heated to 230°C for pouring and spreading or for spreading mastic asphalt screed. The advantage of this screed is its resistance to water and steam.
The mixture also has a low thermal conductivity. Together with its impact sound insulating character, this type of screed often appears to be ideal for attics. Moreover, it is quickly ready.
However, there are also disadvantages: before wood, linoleum and other floor coverings are applied, a barrier layer must be created in order to avoid chemical interactions. Mastic asphalt screed should also not come into direct contact with mineral building materials.
Mortar water, for example, which has a highly alkaline character, is harmful to the mixture of substances. For masonry or other mortar applications, there must therefore be a separating layer between the mortar and mastic asphalt screed.
Synthetic Resin Screed
The synthetic resin used for synthetic resin screeds is usually epoxy resin. However, other plastics can also be used. Synthetic resin screed is not often used, which is partly due to its high price. Only if extremely short drying times are necessary or an increased dynamic load capacity is to be expected during subsequent use.
Although the advantage is that the screed is resistant to water, it is also discredited. Bisphenol A, one of the hardeners that can be used in synthetic resin screed, has fumes that make man infertile.
Calcium Sulphate Screed
Calcium sulphate screed is also colloquially called gypsum screed, because instead of cement as in concrete, calcium sulphate hemihydrate is used as binder. If this comes into contact with water, calcium sulphate dihydrate, i.e. gypsum, is formed.
The term anhydrite screed is also common. Sometimes calcium sulphate screed is preferred to cement screed, especially on larger surfaces. Because a lowering at the edges or the middle is to be expected here less. However, this screed is more susceptible to moisture, especially to permanent moisture with the risk of mould.
The last of the five screeds is the magnesite screed, which was formerly often called stone wood. Magnesite was mainly used for screeds after the Second World War, as cement was only sold / distributed rationed.
Therefore, the mixture of magnesia and magnesium chloride can be found in many corresponding old buildings. Instead of sand, wood was used as chips or flour. This is also the reason for the biggest disadvantage of this screed: a high susceptibility to moisture and wetness. For the garden and the terrace it is absolutely nothing!
What does the term useful screed mean?
Useful screed refers to screeds that are used directly as flooring without the application of floor covering. Especially in industry and halls (warehouses, trade fairs, machine halls), no further floor covering is applied to the concrete or cement screed.
To make this type of substrate durable for a long time and to reduce maintenance to a minimum, you can use concrete sealing as a successful method, among other things. In addition to the corresponding screeds, our products and processes can also be used directly for concrete. If you have any questions, please contact us or one of our user partners.
Difference between concrete and screed – Summary
If you were simply looking for an answer to the question“What is the difference between concrete and screed? We hope that we have been able to help you in your search for answers on the subject of construction, house and garden.
Further details, DIN codes, procedures, advantages and disadvantages of the individual screeds can also be found on Wikipedia and the sources listed there. This encyclopedia entry helped this article. If you have further questions on the subject of concrete and are looking for answers, visit us from time to time – this guidebook area is constantly being expanded!
We hope that now all questions are answered and that you have all necessary information for the construction of the desired underground. If you are looking for further information on concrete, building, sealing and similar topics, please have a look at our other articles.