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.