Pouring the concrete slab may appear to be the biggest part of a concrete project, but it’s only the beginning. A proper finish will leave your concrete in the correct condition to cure completely, reaching the greatest amount of strength possible for the stone. The finishing process also allows you to choose the ultimate look of the concrete. This includes the opportunity to create a smooth concrete finish. Usually this requires hours of grinding and polishing a hardened surface. With the proper tools however, you can create a smooth concrete surface without waiting for a completed slab.
- Skill level:
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Things you need
- Wooden screed
- Magnesium float
- Concrete edger
- Concrete groover
- Steel trowel
Level the surface of the concrete with a wooden screed directly after completing the pour. Drag the flat-bottomed screed bar across the surface of the concrete in a back and forth sawing motion to spread the concrete levelly and to drag excess concrete off the side of the slab. Screed until the slab appears flat. Use the wooden forms surrounding the concrete slab to set the level of the screed, placing the edge of the screed across the top of the forms.
Float the levelled concrete with a magnesium float. The bull float helps to distribute the aggregate (gravel) contained in the concrete evenly across the slab and drags moisture contained within the slab to the surface. The moisture extends the curing time of the concrete, allowing it to complete the hardening process. In addition, the float levels the surface further, filling any holes or lines left in the surface from the screed. Use two complete passes with the float for even distribution.
Wait for the water brought up by the float to reabsorb into the concrete. Press the ball of your thumb into the concrete surface when the water disappears to test the hardness of the concrete. The concrete is hard enough to continue finishing when the imprint of your thumb remains about one-fourth-inch deep.
Edge the slab using a concrete edger. Place the edger between the slab and the form so that the interior curve of the edger is flat against the corner of the slab and the flat of the edger makes a slight mark in the surface of the top of the slab. Run the edger along the edge of the concrete slab to create a bevelled curve around the perimeter. Watch the flat of the edger to make sure the line created by the flat is a light one that does not cut into the surface of the concrete. Remove the edger after rounding the perimeter.
Create a groove one-fourth the depth of the slab using a concrete groover. The groove provides an area for the concrete to expand and contract and prevents cracks throughout the slab. Create a groove only if the slab is 12 feet wide or more. Cut one groove horizontally every 12 feet. Place a straightedge across the surface of the slab and press the blade of the groover into the concrete along the straightedge with the flat of the groover on the surface of the slab. Pull the groove through the slab to cut a line through it along the straightedge. Remove the groover at the edge of the slab.
Float the concrete again to remove any marks.
Trowel the surface of the concrete to create the final smooth finish. Hold the trowel nearly flat against the surface of the concrete, slightly tilted to avoid gouging the concrete with the leading edge of the trowel. Make a pass over the surface of the concrete, pressing slightly with the trowel flat to remove any traces of lines on the surface of the slab. Complete a pass over the entire concrete surface and then do another pass. Apply a third pass with the trowel to create the smooth concrete finish. With each pass, tilt the leading edge of the trowel farther upward to avoiding marring the surface and leaving trowel lines, and increase the applied pressure.
Allow the concrete to cure for three weeks before using.
Tips and warnings
- Always protect your skin when working with concrete, because it can cause skin burns.
- Smooth concrete floors can be slippery when wet.
- Over-trowelling the concrete can cause a chatter texture, or a rippling effect, on the concrete surface.
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