How to Pour a Concrete Sidewalk (page 2 of 4)

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Preparation

Use Cheap Hardboard Siding To Form Even The Tightest Curves
Straight concrete forms are generally made with sturdy 2-by lumber, but curves call for a more flexible material. Concrete pros use 12-in. hardboard siding (sometimes called Masonite) ripped down to 6-in. strips in 16-ft. lengths. Full-service lumberyards and home centers carry all this forming material as well as reinforcing mesh and expansion strips you’ll need.

Roughly measure the length of the walk and divide it by 16 to get the number of siding pieces needed. Siding’s cheap, at about $10 per 16-footer, so buy an extra length to make sure you have enough. Also, pick up enough wood stakes to anchor each side of the form every 3 ft., a 1-lb. box of 1-1/4 in. drywall screws for anchoring the forms to the stakes and enough 6-in. (the size of the grid openings) steel reinforcing mesh to lay in the whole sidewalk trench.

TIP: Getting the long, flimsy strips of siding home from the lumberyard is tricky, even in a pickup truck. Buy a 16-ft. 2x4 to stiffen the stack of siding and wrap packaging tape around the whole works for the ride home. Don’t forget to staple a red flag to the end of the load for safety. Later on, you’ll use the 2x4 for making temporary forms called bulkheads.

Order The Right Concrete Mix
Order the concrete a few days ahead. If rain threatens, you can usually cancel up to two hours before delivery. Although dispatchers are quite helpful, you should at least know the basics before you call:

Calculate the right volume. Concrete is always ordered in cubic yards. First figure out the cubic footage, then convert to yards by dividing by 27. Here’s how: Multiply the length of your sidewalk times the width times the depth (4 in. = . 33 ft.) and divide the total by 27. Using our sidewalk as an example: 60 ft. (long) x 4 ft. (wide) x .33 ft. (deep) = 79.2 cu. ft. ÷ 27 = 2.93 cu. yds. Concrete is cheap and nothing’s worse than coming up short (except rain). A good rule of thumb is to order an extra 5 percent rounded up to the next 1/4 yd. to handle spillage and uneven bases.
Order from the nearest supplier. Get fresh concrete mixed near the site, not mixed across town by some company with a lower price.
Ask for 5 percent “air entrainment” in the mix. Suppliers add a chemical that traps microscopic air bubbles to help the concrete handle the expansion and shrinkage caused by climatic changes such as freezing.
Get the right strength. Tell them you’re pouring an exterior sidewalk and they’ll recommend the correct “bag mix” (ratio of cement to gravel and sand). In cold climates, they’ll probably suggest at least a 3,000-lb. mix. That means concrete that’ll handle a 3,000-lb. load per square inch without failing.
Have your checkbook ready. You’ll have to pay on delivery after the concrete’s unloaded.

The truck comes with the concrete premixed with the correct water content. But the driver may send a little concrete down the chute and ask if you’d like more water added. Unless the mix is too dry to get down the chute, forget it. The mix should be thick—not runny. Wetter mud may be easier to place (fill the forms), but the wetter the mix, the weaker the concrete.

Keep Your Finished Sidewalk Dry—Slope The Forms
Our sidewalk path’s consistent, natural slope away from the house toward the street provided good drainage. So we made the forms level from side to side. If your grade has dips or level sections, slope the sidewalk in those areas by dropping one side of the forms 1/4 in. for each foot of sidewalk width. A 4-ft. wide sidewalk should have one edge about 1 in. lower than the other in level areas to prevent ponding or ice accumulation during the winter.

Here’s How To Keep Your Sidewalk Crack-Free
For a long-lasting sidewalk, plan on a 4-in. base of gravel under 4 in. of concrete. If you live in a frost-free climate with a natural sand base with good drainage, you can pour right on top of the sand. But other soil types will expand and contract with weather conditions and can crack overlying concrete. Gravel protects concrete from these shifting conditions.

Just about any gravel works well, but 3/4-in. crushed rock is easy to shovel and packs well so you can run heavy wheelbarrows on it without the wheels bogging down. Look for a supplier under “Sand and Gravel” in the Yellow Pages. Gravel is ordered by weight, not volume like concrete. We paid $21 a ton (about 1.4 cu. yds. in a ton) plus a $60 delivery charge to have it dumped in the driveway. Divide the gravel volume by 1.4 to calculate the tonnage to order (see “Order the Right Concrete Mix” for help).