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How to Finish Concrete

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How to Finish Concrete

There's more to concrete than just pouring it out and watching it harden. Here's what you need to know to shape and smooth fresh concrete into an attractive, long-lasting surface.

Steps

Level concrete with a screed board

Level concrete as you pour with a screed board (a straight 2x4 about 1 ft. longer than the width of the sidewalk). Start leveling out the concrete as soon as you've finished pouring it. Rest the screed board on the forms and use a sawing motion while pulling the board toward the end of the pour. Fill lower areas with fresh concrete and repeat screening over the same area.


Smooth with a bull float

Draw a bull float over the fresh concrete immediately after screeding to force down aggregate and raise cream (gravel-free concrete) near the surface for finishing. Work in the opposite direction of screeding and push the bull float away from you, slightly lifting the leading edge, then pull it back while lifting the back edge.


Finish with a mag float

Wait until any bleed water disappears and hand float the surface with a magnesium float, starting at the beginning of the pour. Use sweeping motions, lifting the leading edge of the float slightly.

Round over the outside corners with an edging tool. Use a back-and-forth motion in a 1- to 2-ft. area, lifting the leading edge on each pass and working your way down the sidewalk edge. Smooth any ridges with the mag float.

Cut in control joints

Cut in control joints every 5 to 6 ft. with a groover. Plan your cuts by measuring the length of the pour and evenly dividing it so all the segments are about the same length. During the first pass, use a straight board held perpendicular to the forms for guiding the groover.


Broom the concrete

Gently rest the broom on the far side of the sidewalk and slowly pull it toward you and off the edge of the form. Work your way down to the end of the sidewalk, overlapping previous sweeps about 6 in. If clumps of concrete start gathering or you feel the texture is too rough, the concrete is still too wet to broom. Go over broomed areas with the mag float to smooth out marks, and try again in 15 minutes.

In order to have a strong sidewalk that won't scale, spall or crack, cover the sidewalk with plastic sheeting after brooming. Cover the concrete once your fingertip no longer leaves an impression.

Tips
Make sure you have a few helpers lined up for big jobs. Concrete hardens fast, especially on warm days.

Warnings
Wet concrete on skin can cause everything from mild redness to third-degree, permanently disfiguring chemical burns. A few drops of concrete isn't dangerous, but avoid practices like working in concrete-sodden clothes, concrete-filled boots or gloves wet with concrete juice.
Wear tall rubber boots if you have to wade in wet concrete.
Wear gloves (rubber gloves are the safest bet).