Building a Concrete Walk
Building a concrete walk involves three projects: setting the forms, mixing and pouring the concrete, and finishing the concrete. The strength of the slab depends upon materials below the surface. A slab usually sits on a 4-inch gravel base that provides drainage. Wire mesh running through the slab ties it together and helps prevent cracking when the ground shifts underneath. The surface of the concrete has two kinds of joints, an expansion joint is a thick strip of resin-soaked felt put between the walk and existing structures so that they can expand, contract, and settle at their own rates. A control joint is a groove put in the wet concrete to form a weak spot: Any cracks that do form are likely to form along the weak spot, where they will be less obvious. To mix concrete for a 4-foot\-wide walk, 10 feet long, use about 10 cubic feet of concrete. A 90-pound bag yields about 2/3 cubic foot. You'll need at least 15 bags-nearly 3/4 of a ton-and that's before you add water.
- LAY OUT AND EXCAVATE THE WALK
- LAY OUT THE OUTSIDE OF THE FORMS
- MARK THE STAKES
- PUT IN AN EXPANSION JOINT
- LAY WIRE MESH
- MAKE A RAMP
- RELEASE TRAPPED AIR
- LEVEL THE CONCRETE
- ROUND THE EDGES
- CUT CONTROL JOINTS
- FLOAT THE SURFACE AGAIN
- BROOM THE SURFACE
- LET THE CONCRETE CURE
LAY OUT AND EXCAVATE THE WALK
Lay out the walk with batterboards and masons line. Remove the sod and dig out 8 inches of soil across an area 1 foot larger than the pad in each direction. Compact the newly exposed surface with a power tamper. In areas that require a gravel bed (most do; check your local codes), spread gravel on the surface in 2-inch layers. Compact each layer and continue adding gravel until the gravel bed is 4 inches thick.
LAY OUT THE OUTSIDE OF THE FORMS
Install a second set of layout lines on stakes. Position the stakes outside the first set of lines, offset from the first set by the thickness of the forms youll use. Level the lines with a line level or water level. Drive stakes along the layout lines, putting them at the corners of the walk and every 2 feet in between. Drive the stakes straight up and down and firmly embed them in the ground. Youll trim them to height later.
MARK THE STAKES
The walk must slope away from the house at a rate of 1/8 to ¼ inch per foot; check your local codes for the proper amount. Measure down from the batterboards and mark the corner stakes at the finished height of the walk. Hold a chalk line tight at the marks you made, and snap the chalk line to mark the rest of the stakes. Align a 2x4 with the marks on the stakes and nail it in place with two duplex nails. Brace the 2x4 with a 3-pound sledgehammer while you nail. Nail the rest of the stakes to the form the same way. Cut the stakes flush with or just below the top of the forms.
PUT IN AN EXPANSION JOINT
If the walk butts against existing concrete, place a 1/2x4-inch expansion joint between them to allow each structure to move separately if the ground shifts. Attach the expansion joint to the structure with masonry nails or construction adhesive. Brush a form-release agent on the inside of the form so it is easier to remove after the concrete has set. Splice boards together, if necessary. On sides too long for a single board, butt two boards together. Cut a strip of ½-inch plywood and nail it across the joint. Drive a 2x4 stake at each end of the plywood strip and nail it to the form with duplex nails.
LAY WIRE MESH
Lay wire mesh to help prevent the walk from cracking. Position the mesh in what will be the middle of the slab, using wire supports (sold separately). Mesh has a natural curve; set it so it curves down at the ends. If one piece of mesh isnt enough, splice two pieces by overlapping them 6 inches and securing them with tie wires. Dont let mesh touch the forms. Cut it to fit, if necessary.
MAKE A RAMP
Rest a 2x8 or wider board on a concrete block so the wheelbarrow wont dislodge the forms. Also lay boards between the site and where the truck will park. Paint the forms with a release agent such as vegetable oil. When the concrete is ready, carefully dump it in the farthest corner of the form. Place subsequent loads against the preceding load so the fresh concrete will mix seamlessly with whats already there.
RELEASE TRAPPED AIR
Once youve filled the forms with concrete, work it with a shovel, especially near the edges, to break up air pockets. Pull at the wire mesh with a rake until it settles in the middle of the slap. Tap the corners and edges of the forms with a hammer to help release trapped air.
LEVEL THE CONCRETE
Use a straight 2x4 to level or screed the concrete. Move the screed in a sawing, back-and-forth motion across the walk. Make a second pass to finish leveling the concrete. Slide a special trowel, called a darby, over the surface of the concrete. Move the tool in overlapping arcs, adding a slight sawing motion. Stop when a water sheen appears on the surface.
ROUND THE EDGES
When youve finished floating, separate the concrete from the forms by running the tip of a pointing trowel between the two. Slide an edger along each edge of the walk, lifting the leading edge of the tool to avoid marring the concrete. The edger rounds the edges to help prevent chipping
CUT CONTROL JOINTS
Lay out shallow grooves for control points, marking their location on the forms. Space them 1 ½ times the width of the walk, or every 6 feet for a 4-foot-wide walk. Put the jointer at each mark. Then put a straight board long enough to span the forms next to the jointer and guide the jointer along the board.
FLOAT THE SURFACE AGAIN
Floating pushes down surface aggregate and brings a film of mortar to the top. Use a wood float for a rougher surface; use magnesium for ease. Float as before, raising the leading edge of the tool upward to avoid digging into the concrete. Stop when a water sheen appears on the surface. This can be the final surface of your walk.
BROOM THE SURFACE
Brooming the concrete isnt required, but it creates a nonslip surface on walkways. Float the concrete first, then pull a dampened stiff-bristled broom across the surface, perpendicular to traffic flow. This creates small grooves that increase the grip on the walk. The longer you let the concrete dry with brooming, the finer the surface will be.
LET THE CONCRETE CURE
Cover the concrete with plastic to keep water in the concrete while it cures. Concrete that dries too quickly may crack. Let the concrete harden for at least five days before removing the plastic and forms. Pull out the duplex nails with a hammer. Cover any imperfections on the sides of the forms with a slurry made of portland cement and water, then trowel with a steel trowel. Fill around the edges with soil and replace the sod put aside earlier.
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Skill Level: Intermediate
Time: 4 hours
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