Step 1: Start with a sledgehammer
Start with a sledgehammer
A 10-lb. sledgehammer is usually all you need to bust up that nasty old pad (and get a good workout in the process). To protect the house from flying chips, cover any nearby glass with a sheet of 1/2-in. plywood (shown at left). And be sure to wear goggles to protect your eyes.
A few swings with a sledgehammer will let you know right away if you need to call in some heavier equipment. A rental jackhammer will break up a slab much faster than a sledgehammer, with fewer blisters and less sweat. For a small slab, rent an electric model rather than a pneumatic hammer. Rental fees will be about $80 for 24 hours.
Step 2: Build the form
Build the form
Using straight 2x4s, lay out the form’s three sides and screw them together. Take diagonal measurements to check for square (if they’re equal, the form is square). Drive stakes-one every 3 ft.-along the outside of the form, being careful not to bend the 2x4s. Level the 2×4 that runs parallel to the house and drive screws through the stakes and into the 2×4 to hold it in place. Next, be sure the sides of the form slope away from the house 1/4 in. for every foot and screw through the stakes to secure them.
Step 3: Pin the pad to the foundation
Pin the pad to the foundation
Using a hammer drill and masonry bit, drill 1/2-in. holes 4 in. deep in your home’s concrete foundation and space them about a foot apart. Then, using a hammer, tap 12-in.-long pieces of 1/2-in. rebar into the holes to connect the new pad to the foundation. The rebar will ensure that your new pad maintains its slope away from the house. Note: Not all municipalities allow this practice, so check with your local building inspector.
Video: How to Pour a Concrete Slab
Step 4: Level the wet concrete
Level the wet concrete
To get a nice, flat surface that’s perfectly sloped, find a straight 2×4 that’s a foot longer than the width of the form and set it on top of the form as you start pouring the concrete. Use it to level the wet concrete by pulling it from the house toward you while working the board side to side-a process called ‘screeding.’
The mix should be slightly higher than the top of the form when you start. Poke the mix with a shovel to work out any air pockets, especially near edges and corners. For a smoother finish on the pad’s edges, tap the sides of the form with a hammer.
Step 5: Float the concrete
Float the concrete
Start smoothing the concrete-also called ‘floating’-with a magnesium (mag) float. They cost about $25 at home centers. Do this when the concrete has started to set up and you can push your finger into it only about 1/4 in. To float hard-to-reach areas, kneel on a 2×4 laid across the form (see Photo 4). Make long, sweeping strokes in an arc with the leading edge of the mag float lifted slightly. Try to finish this step within an hour of starting to pour the concrete. If it’s hot and dry outside, you’ll have to work even faster.
Step 6: Round over the edges
Round over the edges
Fifteen to 30 minutes after screeding, use a steel edging tool-about $6 at home centers- to smooth and round over the edges of the pad. This gives a nice-looking shape to the edges and forces the aggregate away from the corner. Do this a few times during floating (see Photo 5) and after.
Reinforcement Isn’t Required, But…
For a small concrete pad-less than 40 sq. ft.- you don’t normally have to bother installing steel reinforcing bar (rebar). However, doing so adds strength and crack resistance to the pad if you lay out the rebar in a grid pattern 2 ft. on center.
You’ll find 10-ft. lengths of rebar for about $5 each at home centers, and you can cut them to size with a hacksaw or an angle grinder. You’ll also need tie wires and a wire-twisting tool to connect the pieces of rebar in a grid pattern. Get more information about reinforcing concrete with rebar.
Step 7: Add texture with a broom
Add texture with a broom
Use a special concrete broom or any stiff-bristle broom about 15 minutes after floating to add a slip-resistant texture to the top of the pad. The coarser you want the texture, the earlier you should broom. The grooves created by the broom should follow the direction of the slope so water runs off easily. Brooming also hides imperfections in float work.
Four Things to Know About Concrete
- Too much water weakens concrete: If you mix too much water with concrete, cement crystals form farther apart, leaving concrete weak and porous. That can cause trouble later as pores and pockets fill with water, freeze and break up the concrete’s surface. With the right amount of water, cement crystals grow tightly together and interweave to form strong, watertight concrete.
- Floating too soon leads to trouble: As concrete sets, water rises to the surface. Left alone, this ‘bleed water’ is reabsorbed into the concrete. But if you float the watery surface, you’ll force the aggregate and cement down, leaving a watery mix of sand and too little cement on top. Wait for the bleed to disappear before floating. Also, don’t overwork it. Too much floating (or troweling) will lead to a less durable surface.
- The longer it stays damp, the better: Concrete doesn’t harden because it’s drying; it hardens because it’s wet. The longer concrete stays damp, the harder and stronger it gets. The hardening or ‘curing’ process can continue for weeks if the concrete dries slowly. Covering it with a sheet of plastic also slows the curing process.
- It can burn your skin: Some people get concrete on their skin and don’t have any problems, but others are more sensitive to it. Until they cure, all cement-based products have the potential to leave minor burns on your skin. Play it safe and wear a long-sleeved shirt, long pants, boots and waterproof gloves when working with concrete.
Step 8: Cover the pad
Cover the pad
To prevent the concrete from cracking while it’s curing (hardening), cover it with a plastic sheet to slow the process. Wetting the pad with a fine spray of water every two to three hours for the first day helps too. Higher temperatures require more frequent wetting. The more time concrete has to cure, the stronger it will be.
Order the Right Concrete Mix
Bagged concrete vs. ready-mix:
Most small pads require less than one yard-27 cu. ft.-of concrete. You can buy several bags at the home center, which you’ll have to lug home, mix with water and pour yourself. It’s a lot of work, but it might make more sense financially for a small pad at the bottom of your deck stairs. For bigger pads, have ‘ready-mix’ concrete delivered. It comes mixed with water and the delivery guy will pour it right into your forms. Prices vary by region, but expect to pay about $300 for 1 yard. Order it a few days ahead. If rain threatens, you can usually cancel up to two hours before delivery.
Order the right concrete mix:
- Plan to pour a pad at least 4 in. thick and calculate the right volume. Concrete is ordered in cubic yards. Many suppliers have calculators on their website, but it’s fairly easy to figure out how much you need. First figure out the cubic footage, then convert to yards by dividing by 27. Here’s how: Multiply the length of your pad by the width by the depth (4 in. = . 33 ft.) and divide the total by 27. Order a little bit more than you need. 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 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 accommodate the expansion and shrinkage caused by climatic changes such as freezing.
- Get the right strength. Tell the dispatcher you’re pouring a pad and they’ll recommend the correct ‘bag mix’ (ratio of cement to aggregate and sand). In cold climates, they’ll probably suggest at least a 3,000-lb. mix. That means the concrete can support a 3,000-lb. load per square inch without failing.
- Have your checkbook ready. You’ll have to pay after the concrete’s unloaded.
The truck arrives 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. It should be thick-not runny. Wetter mud may be easier to place (fill the forms), but the wetter the mix, the weaker the concrete.