Page 26 - Build 165

GUIDANCE ON CONCRETE SURFACE FINISHES SELECTION AND PRODUCTION
BUILD
O -the-form concrete surface nishes
Successful processes to achieve the desired concrete surface nish are now mainstream and can be reproduced by capable tradespeople.
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BY CONCRETE NEW ZEALAND INC.
Form linings can be used to create attractive surface designs.
and de nes limits for the various grades of nish, including:
● surface plane variations
● colour variation
● physical irregularities
● the X factor (for exceptions)
● provision of sample reference panels.
O -the-form nishes
This category covers the concrete surfaces that are dependent on the formwork for texture and nish. The formwork dimensions, rigidity, joint tightness and texture all become of increasing importance. Time spent before casting to ensure the exactness of all the above is invaluable. The six classi cations (F1–F6) cover all qualities of formed nish.
They range from hidden surfaces (F1 such as foundations, the rear of retaining walls and lined surfaces), plaster surfaces (F2) and exposed surfaces viewed from afar (F3) to architectural and high-quality panels (F6).
Although there is a grey scale included in the standard, there are no speci c limits set for the variations accepted under each nish. It is up to the speci er to determine an acceptable range and to monitor this with a sample reference panel. Any nish that has a nominated colour range restriction must be designated with the X su x and the range speci ed.
Exposed aggregate nishes
Surfaces in this category have exposed aggregate on their surface. The speci cation extends the
NZS 3114:1987 Speci cation for concrete surface nishes provides the format for the speci er’s concrete nishing requirements to be communi- cated to the contractor. The application of the standard permits appropriate qualities of nish to be assigned to all surfaces, and attention is drawn to speci c requirements.
Guidance in the standard
NZS 3114:1987 covers the di erent methods in which the surface is prepared:
● Finishes that are formed and thus mirror the
characteristics of the form are F nishes and are described in part 1, o -the-form nishes.
● Exposed aggregate nishes, whether formed or otherwise, are described in part 2, exposed aggregate nishes. This section refers to parts 1 and 3 using the su x E.
● Unformed surfaces are generally laid horizontally and incorporate screeding, oating or trowelling during production. These surfaces are described in part 3 and include oors, slabs, exterior pavements and inverts (surfaces that remain exposed when concrete casting is complete) and are classi ed as U nishes.
The standard provides guidance on the character- istics that can be expected to a ect the nish
24 — April/May 2018 — Build 165
PHOTO – JACKSON INDUSTRIES AND HENRIATA NICHOLAS