Like a front door, a home’s front walk is a welcoming feature. So if your walk is settling or crumbling, you should consider replacing it. True, it’s tough work, but it can be accomplished in five distinct steps: demolition, grading, forming, placing, and finishing. But one word of advice before you start: Order the right concrete. For walks, this means an exterior-grade 2500- or 3000-psi mix with air-entraining agents added. These agents form microscopic air pockets in the concrete as it cures, and this allows ice crystals to develop in cold weather without damaging the concrete’s surface.
This project was originally published in the January 2001 issue of Popular Mechanics. You can find more great projects at Popular Mechanics DIY Central.
Step 1: Demolition and Grading
Our old concrete walk was a victim of poor site preparation and design. Uncompacted base material had settled under the walk, tipping it toward the house. Because the walk was pinned to the front stoop with reinforcing bar, it settled and cracked.
We removed the entire walkway using a 120-volt electric jackhammer. This tool made short work of it and was well worth the $50 rental fee. When using the jackhammer, start at an outside corner and work in, chipping away 8-in.-wide pieces (see inset photo). About the only pleasant surprise in this job was that once the walk was removed, we found that the soil underfoot was firm and needed no further compaction.
If this is not the case with your walk, you must compact the soil—and you may need to place crushed stone on top of it. Check with your local building department or a concrete supplier to see what materials and methods work best where you live.
Step 2: Forming
We began our concrete form at the stoop. We cut a 1⁄2-in.-deep x 4-in.-long rabbet in the end of a 2 x 4 that was used for the form’s straight section. A curved portion of the form fits into the rabbet in the 2 x 4. Position the 2 x 4 form in two steps. First, measure from the wall of the house to establish the walk’s width, then run a string line parallel with the house wall.
Next, drive a handful of equally spaced stakes along the string line and fasten the 2 x 4 form to the stakes using 2-in. long drywall screws. Snap a chalkline on the house wall to establish where the walk’s surface will be, and use a 4-ft. mason’s level to set the form 1 in. below the line. This slopes the walk to drain water away from the house.
Next, install the remaining stakes so that when all the stakes are placed, they are about 18 in. apart (Photo 1). Each stake should be screwed to the form.
The curved form material is 4 in. wide and sawed out of a piece of 1⁄2-in.-thick hardboard siding that is 12 in. wide. Fasten the hardboard into the form’s rabbet and curve it, staking it in place as you go (Photos 2 and 3).
Our walk was poured directly against a brick wall (yours may or may not be), so we had to provide a means for allowing the walk to move freely without damaging itself or the house. To provide for this, tape a 1⁄4-in.-thick foam rubber isolation strip to the wall just below the chalk line (Photo 4).
The next step of form setting is a bit tricky. Concrete is placed by way of a process known as screeding. That is, you remove excess concrete from the form by slicing it off using a 2 x 4 (called a screed board). The screed board is held on edge and slid along the form. The problem here is that there isn’t a second side of the form on which to rest the screed board.
To solve this problem, install a 3⁄4-in.-dia. pipe on stakes, a then slide the screed board along it. Hammer each pipe stake into the ground about a foot away from the wall (Photo 5). Drive two angled nails into the top of each stake to hold the pipe. Place the pipe on the stakes, then check it with a level and screed board (Photo 6). Tap the pipe down at each stake until the screed board meets the chalkline. Now you're ready to place the concrete.
Step 3: Placing the Concrete
If it’s a hot day, dampen the base on which the concrete is placed. This slows the concrete’s curing slightly and buys you a little more time to finish it.
In most cases, a concrete walk is too wide for you to reach across, so use something to distribute your weight on the wet concrete, and to prevent you from touching it—concrete is highly alkaline and can burn your skin. Foam insulation board works well for this because it also cushions your knees.
Also keep in mind that concrete trucks are too heavy to park in a driveway, so you will need to bring the concrete to the form in a wheelbarrow. Wheel the concrete to the front of the form, and carefully pour it out (Photo 1). Use a square-nose shovel to place the concrete where needed, then use the screed board to pull off the excess. Reset the board, and saw it back and forth across the form (Photo 2).
Place about 4 linear feet of concrete, and slide the screed pipe back on its stakes. Pull out the exposed stakes with pliers, and sling concrete into the groove left by the pipe and stakes. Then, level the area with a wood or magnesium float. Continue until you’ve placed and screeded the entire walk. Now, take a break, and clean your wheelbarrow, shovels and screed pipe.
With that done, smooth the surface with a float (Photo 4). Don’t overdo it, however. The float’s job is to push the aggregate down and work portland cement to the surface. With too many passes, you’ll push the rocks too low and bring up too much cement. This makes the surface weak. Just make a couple of sweeps and back away.
Step 4: Finishing the Concrete
Now it’s time to finish the edges and cut control joints. Press an edging tool into the concrete against the form. Push forward a foot or two, and examine your work (Photo 1). If the tool presses in deeply, tips out of level and leaves behind water, wait 20 minutes and try again. If the edging tool stays level and the corner rounds off smoothly, finish all the edges.
Next cut the control joints. Concrete always cracks, and control joints allow us to choose where the cracks will appear. A control joint’s depth is about a quarter of the concrete’s depth, so use a groover with a blade 3⁄4 to 1 in. deep. Run the groover along a plank to ensure a straight joint (Photo 2). A rule of thumb for control-joint spacing for sidewalks is to space them roughly equal to the walk’s width. In our case, they were about 4 ft. apart.
After the slab is floated, edged and grooved, trowel it smooth. Try troweling as soon as you finish the control joints. If one or two passes with a trowel leaves behind water and tool marks, wait 15 minutes and try again. First, trowel the edges smooth to remove ridges left by the edger and groover. Sweep the trowel away from the control joints, and when these surfaces are dressed up, trowel the rest of the walk. Hold the trowel nearly flat, and sweep in wide passes in front of you (Photo 3). Give the concrete a little time to harden, then gently drag a push broom across it to leave a slip-resistant surface (Photo 4). If the broom makes the surface look like oatmeal, retrowel that area and wait for a harder set. Cover the concrete with a plastic sheet for two to three days then strip the forms, and fill the isolation joint with self-leveling urethane caulk, available through concrete dealers (Photo 5).
Enjoy your new, durable walkway!