What are exposed aggregate surfaces?
To reach exposed aggregate concrete the first layer of cementitious material is removed so that the aggregates become visible. To control and ease this process the CSE® Deactivator reacts chemically upon surface contact with the fresh concrete during the hydration and stops the cement from hardening there. The fresh concrete below this surface layer hydrates and hardens like normal. Later, usually after 24 hours, the surface can be washed off, which means that the “deactivated” cementitious material is removed by waterjet and the aggregates are revealed. The depth of this wash-out texture is called and specified by the exposure depth in millimetres. Exposed aggregate surfaces can be obtained with different exposure depths varying from approx. 0.5 mm to about 6.0 mm. In the range between 0.5 to 2.0 mm those surfaces are called micro-exposed. The concrete surface has a clear, fresh appearance, as the exposed concrete aggregates become visible and expose their original beauty. That already is the main difference to a sandblast finish, where the concrete surface is revealed by mechanical, abrasive pressure which makes the aggregates lose some of their original colour and shine and that’s why some say sandblasting makes the surface look dull.
What are CSE® Deactivators?
CSE® Deactivators are functional fluids containing active ingredients whose primary task is to prevent the hardening of the cement skin up to a predefined "exposure depth", while the rest of the concrete, beyond the predefined "exposure depth", is left to harden normally. The CSE® Deactivators only react with the cement paste of the fresh concrete and neutralise it.
When should I use a CSE® Deactivator to produce exposed aggregate surfaces?
Use CSE® Deactivators if you are aiming at high uniformity of the exposed aggregate concrete surface texture. Use CSE® Deactivators if you already know and are tired about the limitations of “surface retarders”. And please don’t think they are all the same.
How are CSE® Deactivators used to produce exposed aggregate surfaces?
CSE® Deactivators, can be applied in two different ways.
When the deactivator is applied to the mould surface before the concrete is cast (similar to the application of a mould release agent), it is referred to as a so-called negative or face-down application - widely used in precast concrete applications.
It is also possible to spray the CSE® Deactivator directly onto the fresh concrete, for example after trowelling, as done when using cast-in-place concrete for decorative concrete paving. This is then referred to as the so-called positive or top-surface application.
What is Retarder Paper?
Retarder Paper is a special sort of paper, where one side is coated with a deactivating agent. Its functionality is similar to that of the liquid CSE® Deactivator, also with a variety of different exposure depth coatings, to achieve the desired exposure depth.
When should I use Retarder Paper to manufacture exposed aggregate surfaces?
Retarder Paper are perfect for concrete with simple geometrical shapes and for machine pressed concrete, such as terrazzo paving slabs.