Exposing aggregate from within the precast panel requires application of a chemical retardant coating within the precast mould. As concrete comes in contact with the chemical coating, retardation on the cement occurs resisting hardening of the thin layer of cement in contact with the coating.
once the panel has cured and has been released from the mould, the retarded cement matrix is washed away revealing the aggregate bound within the concrete.
Irregularities in aggregate placement and variable depth of exposure resulting from chemical reaction is a natural phenomenon with retarder exposed aggregate concrete.
Design Tip:
It is recommended to add oxide colour to the cement, to a similar tone complimenting the aggregate, this provides a camouflaging of any naturally occurring irregularities revealled during the exposing process. I.E. If using Black aggregates, Black oxide at a minimum 5% doseage is recommended.
Specifying Exposed aggregate:
When specifying Exposed Aggregate it is a good idea to expand on your intended finish description as the term exposed aggregate can refer to many architectural finishes all with different appearances, properties and costs.
E.g. : “2-5mm Architectural Retarder Exposed Aggregate.
Talk to one of our professional sales people for further guidance on correct specification terminology to ensure you get what you want.
