8.9
Finishing Concrete
Concrete finishing starts immediately after the concrete has been placed and consolidated. The initial step, screeding, involves leveling the concrete…
After consolidating the placed concrete, excess material is removed from the surface and flushed with the formwork's top using a screed.
Subsequently, using a bull float or darby, the high spots on the concrete surface are lowered, low spots are filled, and large aggregates are embedded in the concrete before bleed water rises to the surface.
Once the sheen from the bleed water on the surface disappears upon evaporation, it is ready for final finishing. This begins with edging, which involves rounding off the concrete's edges.
It is followed by jointing, where control, isolation, and construction joints are strategically located in the structure.
Next, a handheld float or power float is used to remove any surface imperfections resulting from edging and jointing, embed the aggregates slightly within the concrete, and remove the excess water, keeping the surface open.
Lastly, the finished surface may be textured by troweling to create a hard and smooth surface, brooming to make it rough and slip-resistant, washing the excess cement paste on the top to create an exposed look, or patterned by inserting divider strips.
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Q1: What is the purpose of screeding in concrete finishing?
Screeding removes excess concrete material from the surface and flushes it level with the formwork's top. This initial leveling step prepares the surface for subsequent finishing operations and ensures a uniform base before bleed water appears, which can cause scaling and dusting if not managed properly.
Q2: How do bull floats and darbies improve the concrete surface?
Bull floats and darbies smooth the concrete surface by lowering high spots, filling low areas, and embedding large aggregates within the concrete. These tools work before bleed water rises, ensuring a properly prepared surface ready for final finishing techniques and preventing surface defects.
Q3: Why is bleed water important to monitor during concrete finishing?
Bleed water must evaporate completely before final finishing begins, as its presence can lead to scaling and dusting on the concrete surface. Once the sheen from bleed water disappears, the concrete is ready for edging, jointing, and floating operations that create the finished appearance.
Q4: What role do control and isolation joints play in concrete finishing?
Control, isolation, and construction joints are strategically located during jointing to manage the concrete's natural movements and prevent unsightly cracking. These joints accommodate expansion and contraction, protecting the structural integrity and appearance of the finished concrete surface.
Q5: How does floating remove imperfections from the concrete surface?
Handheld or power floats smooth surface imperfections left by edging and jointing, slightly embed aggregates below the surface, and compact the mortar. This process removes excess water while keeping the surface open, preparing it for final texture application and ensuring a durable finish.
Q6: What are the different texture options for finishing concrete surfaces?
Concrete surfaces can be textured through troweling to create a hard and smooth finish, brooming to make it rough and slip-resistant, or washing to expose aggregate for a decorative look. Patterned finishes can also be created by inserting divider strips, allowing customization of the final appearance.
Q7: When should final finishing begin after placing concrete?
Final finishing begins after the concrete has been consolidated, screeded, and the bleed water sheen has evaporated from the surface. This timing ensures the concrete is properly prepared and stable enough for edging, jointing, floating, and texturing without compromising the finished quality or durability.