Hydraulic binders - what is it?

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

In this case, the lime acts 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

Through the discovery of cement as a binder (Opus caementum by the Romans) at around 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 quicklime, 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 to use high-strength concretes for the first time. The addition of so-called pozzolans (a volcanic rock) as a supplement made the concrete even completely waterproof.

Hydraulic and non-hydraulic binders at a glance

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

hydraulic bindersnon-hydraulic binders
hydraulic lime (trass)lime
cementgypsum
plaster and masonry binderclay
mixed binder (trass + blast furnace slag + Portland cement)magnesia binder

Important: Non-hydraulic binders are also hardened Condition not waterproof and moisture resistant!

Other binders

Many other binders are used in construction - including

  • bitumen
  • anhydrite (calcium sulfate / gypsum, used in screeds)
  • emulsion paints (solids are also combined and held together by a binder)
Tips & TricksConcrete Although theoretically with lime as a binder was conceivable as a building material but such a concrete would hardly be good. 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.
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