Details on classifications & specifications for surface finishes
An excerpt from the July/August 2019 issue of Precast Inc., by Eric Carleton, P.E., NPCA's director of codes and standards.
Less is better when spraying concrete form release agents on concrete forms.
In 1975, the International Council for Building Research established a general classification of formed surfaces which is referenced in the most recent edition of ACI 301.2R, "Identification and Control of Visible Effects of Consolidation on Formed Concrete Surfaces."
Those classifications are:
Rough - No special requirements for finishing
Ordinary - surface finishing has a minor factor
Elaborate - definite requirements for visual appearance
Special - highest standards for appearance [considered architectural]
Within ACI 347R-14, "Guide to Formwork for Concrete," there is a similar class system to differentiate concrete surface evaluation based on application:
Class D - minimum quality requirement for surfaces where roughness is not objectionable, usually applied where surfaces will be permanently concealed.
Class C - general standard for permanently exposed surfaces where other finishes are not specified
Class B - intended for coarse-textured, concrete form surfaces intended to receive plaster, stucco or wainscoting
Class A - suggested for surfaces prominently exposed to public view where appearance is of special importance
ACI 301-16, "Specifications for Structural Concrete," provides more detailed information.
5.3.3.3(a) Surface finish-1.0 (SF-1.0):
No formwork facing material is specified
Patch voids larger than 1-1/2-inch wide or 1/2-inch deep
Remove projections larger than 1 inch
Tie holes need not be patched
Surface tolerance Class D as specified in ACI 117-10, "Specification for Tolerances for Concrete Construction and Materials and Commentary."
Mockup not required
5.3.3.3(b) Surface finish-2.0 (SF-2.0):
Patch voids larger than 3/4-inch wide or 1/2-inch deep
Remove projections larger than 1/4 inch
Patch Tie holes
Surface tolerance Class B as specified in ACI 117
Unless otherwise specified, provide mockup of concrete surface appearance and texture
5.3.3.3(c) Surface finish-3.0 (SF-3.0):
Patch voids larger than 3/4-inch wide or 1/2-inch deep
Remove projections larger than 1/8 inch
Patch Tie holes
Surface tolerance Class A as specified in ACI 117
Provide mockup of concrete surface appearance and texture
5.3.3.5 Unspecified as - cast-finishes - if a surface finish is not specified, provide the following finishes:
SF-1.0 on concrete surfaces not exposed to view
SF-2.0 on concrete surfaces exposed to view
For the full article, please visit the Precast.org site.