Hydraulic binders - what is it?

Binders are crucial in mortars for the properties a mortar can possess. What distinguishes hydraulic and non-hydraulic binders, and what difference the discovery of hydraulic binders made, read in our article.

lime mortar

Lime mortars are the oldest used building materials among the classic mortars. They harden in the air. With lime mortar you can easily make plasters by mixing sand in the lime.

The lime acts in this case as a binder that holds the mass together. The lime-sand mixture (so-called air lime mortar) then hardens in the air and becomes solid. But such mortars are not very resilient.

Cement mortar and concrete

By the discovery of cement as a binder (Opus caementum by the Romans) at about 200 BC. For the first time, the binding of larger and coarse aggregates was made possible.

Cement does not harden in the air, but also under water and is therefore a hydraulic binder in contrast to the lime, which is a non-hydraulic binder.

Hydraulic binders do not cure by drying in air but by a chemical reaction. This makes a significant difference in the durability and resilience of the resulting building material. The discovery of cement in Roman times made it possible for the first time to use high-strength concretes. The addition of so-called pozzolans (a volcanic rock) as a supplement made the concrete even completely waterproof.

Hydraulic and non-hydraulic binders in overview

In the building materials many different binders are used. Depending on their curing behavior, they can be classified as either hydraulic or non-hydraulic binders.

hydraulic bindersnot hydraulic binders
hydraulic lime (trass)quicklime
Plaster and brick binderClay
Mixed binder (trass + blast furnace slag + Portland cement)magnesia

Important is: Non-hydraulic binders are not waterproof and resistant to moisture even in the hardened state!

Other binders

There are many more binders used on the construction site - these include, for example

  • bitumen
  • Anhydrite (calcium sulfate / gypsum, used in screeds)
  • Emulsion paints (here, too, solids are combined via a binder and held together)

Tips & Tricks

Although concrete would theoretically have been conceivable with lime as a binder, such a concrete would hardly have been suitable as a building material. The water-soluble lime would have led to the first rain, the stone surcharges had fallen apart again and the wall would have dissolved into a pile of stones.

Video Board: Major Hydraulic Binders/Soil Stabilisation