Once concrete has been appropriately laid, it is often important to leave it with a smooth, durable surface. Achieving this means working quickly and paying close attention to the condition of the concrete in order to avoid weak, damaged, or unattractive slabs. After perfecting your pour with the right concrete form rental, the right technique for finishing concrete can be the difference between a satisfactory outcome or a poor one. Keep reading for a guide to finishing concrete effectively.
Gather Your Tools
After pouring concrete and forming it, you will want to begin finishing quickly. It’s good to have all the necessary materials on hand, including:
•A square shovel or come-along
•Screed or straight board
•Bull float or darby
Step 1: Screed the Concrete
As soon as you can, begin pushing or pulling the screed board across your forms. This motion should mimic that of a saw moving back and forth. Be sure to shove the concrete into low spots on the front of the screed board and repeat in order to remove excess concrete. The concrete should end up at the proper grade when you complete this step.
Screeding begins the process of moving larger aggregate below the surface. Any 2×4 that overlaps your form by at least 6 inches can be used, but a square shovel or come-along is recommended.
Step 2: Darby the Concrete
Sweep your darby or bull float across the concrete, using the motion of overlapping arcs. This will flatten the surface, push down lumps, and fill any voids. Life the leading edges slightly while still keeping the darby level with your surface. Make two passes at this step, checking to see that your aggregate is slightly embedded, leaving a slurry of cement and sand to fill the surface.
Your darby should be large enough to reach a little more than halfway across the slab. You can make a darby by screwing a handle onto a straight piece of 1×4 or two handles for better control. If you can’t reach the edges with a darby, you can rent a bull float and handle instead.
Be cautious not to overwork the concrete, which can draw too much cement and fine sand to the top, creating a weak surface.
Step 3: Let Surface Water Disappear
After the previous steps, water will appear on the surface. This is known as “bleed” water and should disappear before you begin edging, floating, or joining the concrete. The water will reabsorb into the concrete on its own.
If you work the concrete before the bleed water is gone, the surface will dry weakly. To test whether the water is completely gone, you can press a gloved finger onto the surface near the edges. This should not leave an impression more than a ¼ inch deep.
Step 4: Edge the Concrete
Once the sheen is completely gone, use an edging tool across the top, working it back and forth. The edge of your concrete form should serve as the guide. Lift your leading edge slightly, using long strokes to work the aggregate back until you have smooth, round edges.
Step 5: Create Grooves
Take a straight board and set it along with predetermined marks for control joints, then run a groover back and forth against the straight edge until the bed of the tool is riding on the concrete surface. This can divide the slab into equal parts. The distance between grooves will depend on the function of the concrete. This will help to control cracking caused by the movement of drying and soil movement.
An effective groove will be at least ¼ the depth of the slab, creating an already weakened spot for cracks to form without being visible.
Step 6: Float and Trowel the Concrete
Sweep a hand float over the concrete, lifting the leading edge slightly, in large arcs. This will compact the surface and can blend in any marks left by the edger and groover. If the concrete is already starting to harden, it’s okay to bear down on the float.
Once the concrete is partially hardened, smooth the surface using a steel trowel. Hold this trowel almost flat and swing it in large, overlapping arcs while applying pressure. Once you are happy with the look, you do not need to continue.
If necessary, you can repeat edging and grooving steps to refine the look of the slab.
Step 7: Brooming
To finish your concrete, drag a broom across the concrete to create a non-slip surface. You can adjust the pressure to change the texture of partially-hardened concrete.