What does the same mean in construction

Cement - mortar - plaster: what's the difference?

Universal binding agent: Cement sacks can be found on all construction sites around the world. Photo: Pixabay

Gray materials such as cement, mortar and plaster are used everywhere in construction. Mixed with water, they result in similar-looking, viscous masses that are used for gluing, filling or filling building materials. You can quickly get confused: What is the difference between cement, mortar and plaster?

The distinction between these three product types is made difficult by the fact that they largely consist of the same raw materials: lime, clay and sand. Nevertheless, cement, mortar and plaster are by no means the same. At least cement differs fundamentally from the other two substances in terms of its function. Cement is a binding agent that, as a component of building materials, ensures that they are cohesive. This binding agent is used in concrete, for example, but also in mortar and plaster.

What is cement

The main components of cement are limestone and clay. A little quartz sand and iron ore are usually added to these raw materials before the mixture is finely ground and fired at 1,400 to 1,500 ° C. This creates small, hard globules - the so-called cement clinker. These are mixed again with other additives such as blast furnace slag, fly ash, limestone and gypsum, and everything is then ground again. Only then is the cement binder ready.

Cement is a gray, powdery substance that only turns into a cement paste when water is added, which becomes rock-hard when it dries. As I said: cement is used as a binding agent in building materials. If you mix it with water, sand and gravel, you get concrete. On the other hand, if you leave out the gravel and only add water and sand, then mortar is created.

From cement to mortar

Refurbishment case: The flaked exterior plaster reveals bricks with plaster. Photo: lichtkunst.73 / www.pixelio.de

We note: Mortar is actually exactly the same as concrete, except that it only contains aggregates up to a maximum grain size of 4 mm, i.e. no gravel. Both materials contain cement. At least that applies to the classic cement mortar. Unfortunately, it's not that simple: there are also types of mortar that contain other binders instead of cement - such as lime. Then one speaks of lime mortar. There is also, for example, plaster of paris, clay, synthetic resin, or a mixed form of lime cement mortar. As you can see, the name is always given by the binders used.

So mortar often contains cement, but not always. In general it can be said that the recipe always includes sand, water and a binding agent. Depending on the area of ​​application, other additives are added for the different product types. Depending on the application, a distinction is made between, for example, masonry mortar, tile mortar (= tile adhesive), adhesive mortar for thermal insulation composite systems and screed mortar. Mortars also include fillers and leveling compounds. And then there is the product group of plasters. It is also about mortar - just plastering mortar.

And what is plaster?

Plaster is the name given to mortar with which walls or ceilings are coated in one or more layers. The basic composition corresponds to that of all other types of mortar: sand, water, binding agent. But in practice there are innumerable plaster products with sometimes very different properties, whereby the differences depend not only on the binding agent, but also on the additives that the manufacturers use. In general, a distinction is made between, for example, base and finish plasters and external and internal plasters.

The most common binders for mineral plasters are lime and cement. Gypsum and clay, on the other hand, are only used for interior plasters because these binders become soft or dissolve with prolonged weathering. Synthetic resin plaster is considered to be very weather-resistant. This also has the advantage - especially compared to cement plaster - that it is particularly elastic and therefore not so prone to cracking.

The example makes it clear that the different types of mortar - with all similarities - have very different properties. For example, masonry mortar must above all be pressure-resistant. In the case of plaster, on the other hand, other properties are required - such as sufficient elasticity and, of course, the appearance of finishing plasters. The manufacturers take care of this with their respective fine formulations.


You can find more about solid construction in the overview


About the author Roland Grimm has been a freelance journalist based in Essen since February 2013 and regularly writes specialist articles for Building material knowledge. Before that, he was a specialist editor at the industry magazine for around six years Building materials market and also editor-in-chief and, from 2010, editor-in-chief of the trade journal building materials practice. Contact: freelance [email protected]

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