Architectural Precast aesthetic appearance is virtually unlimited by varying and combining aggregates, sands, color additives, cement color, applied finish textures, cast in stone, granite and clay products, and reveal patterns/sizes. Early conversations with the architects/owners with regards to creating the desired appearance, setting the expectations and developing a schedule process for samples/mockups is critical for the project’s success.
Typically, a precaster will start with a pre-design sample (12”x12”) to establish the general color and texture for the project. The precaster should communicate a level of expectations to the architect/owner with regards to how the samples are made by quality control technicians in their lab, as the concrete is not provided by a production batch plant mixer, but mixed by other methods, and the concrete strength of a sample will not be that of the mockup or project panels, which could affect the applied finish exposure. The architect should allow sufficient time (7-14 days) for the precaster to develop a requested sample. Once approved, the architect should list the mixture proportions in the specifications and have the pre-selected sample available for all bidders. Keep in mind, the sample select represents only the first step in development of the actual production precast element and should not be considered the final decision for appearance.
After award of the contract, a mockup for production approval will be produced with the approved concrete mix; the minimum panel size should be 4’x4’ and can be as large as a full-scale project panel. Mockups should encompass all finishes (both interior & exterior), reveal patterns/sizes and cast in stone, granite & clay product units per the project construction documents. The mockup panel will be produced by production in forms similar to those the project’s final panels will be cast in. The production facility’s batch plant mixer will supply the concrete, which could vary the color and/or the consolidation of the mix slightly from the quality control lab concrete (pre-selected sample). The contractor should anticipate delivery of the mockup for approval within three to four weeks from award, or the sample approval date. A mockup approval review meeting (at the project jobsite or precaster plant facility) should be attended by the architect, owner, contractor and precaster for the approval process and to discuss any concerns or issues that may arise with the mockup. PCI Plant Certification Standards require the architect/owner to provide a formal “signing off” documentation designating the acceptance of the mockup. The precaster should provide a mockup drawing and the mix design information to the architect/owner to be incorporated into the formal signed document. The approved mockup shall remain on site or be delivered to the jobsite for maintaining quality of the precast for the duration of the project. Remedial work should also be performed on the approved mockup panel for setting acceptable appearance standards.
In addition to these processes, there are other determining factors for a successful precast project in terms of appearances, such as which concrete mixes work better for the different applied finishes (acid etched, retard water-washed, sandblasted & polished) or having repetitive reveal patterns/sizes to complement the panel size/layouts.