Patios or Steps? - Plan the Same Way
Whether planning something small (like steps) or large in scope (like a patio) - calculations for concrete projects of any size are basically the same.
Concrete is measured in cubic yards and project length, width and depth determine the amount needed.
For any size project: Multiply length by width (to find square feet), multiply that by depth or thickness (for cubic feet) and divide by 27 (the number of cubic feet in a cubic yard) to determine how much concrete is required.
- Tip: To avoid running short mid-project, always plan 10 percent more to compensate for below-grade variations and waste.
- Tip: If math is not your strength, you don't have to remember the formulas. Do these conversions using an inexpensive feet-inch-fraction "project" calculator.
Concrete is a mix of sand, gravel, water and portand cement -available three ways: Separate ingredients (that you mix), Pre-mixed (just add water) and Ready-mixed (delivered by truck).
For smaller projects, pre-mixed bags are great cost-wise. Available in two sizes: 60-pound on average costs ($1.35 - $1.80) and 90-pound ($2.00 - $2.30).
However, there is a "point of diminishing returns" - where the number of bags you physically need to prepare for larger projects simply overwhelms the economy of mixing it up yourself.
Do the math: A 10' X 10' X 6" patio needs 1.85 cubic yards of concrete. Using 60-pound bags (yield: one-half cubic foot per) it requires preparing 100 bags. Time to consider ready-mix?
Cost vs. Value
Work-wise, ready-mix is a no-brainer. But what about cost?
Using 60-pound bags, concrete for a patio this size ranges from $135 to $180. You'll need to rent a mixer too which adds another $40 to $60 per day.
Conversely, while calling in ready-mix reduces work, it also boosts the cost. Each cubic yard costs about $65 (minimum order one and no fractional yards). However, a fully loaded cement truck holds 10 cubic yards - and partial "short" loads cost $15 to $20 extra for every cubic yard less than a full load.
So, our 1.85 cubic yard patio first requires purchasing two cubic yards of ready-mix (2 X $65 = $130) - plus another $135 for the "short load" (10 yard full load minus 2 yards = 8 yards "short" X $17 per yard average) - and now totals around $265. With assorted fees added (environmental impact, fuel surcharge, sales tax, etc.) the final cost is about $295.
Not bad. For this project, ordering ready-mix would cost from $55 to $120 more than pre-mixed - depending on where you bought your bags and rented your mixer.
Conclusion: Probably worth it and certainly a lot easier on the back.
Calculation Made Easy
Success centers on knowing how much concrete you need and determining at what point a ready-mixed delivery makes more sense than dealing with pre-mixed bags.
- Tip: A tool called ProjectCalc ® Plus makes it easy. A few keystrokes launch hundreds of home project formulas that figure material and costs with pin-point accuracy. To estimate: enter dimensions, push "convert" and "type of material" to learn how many bricks, blocks, board feet or cubic yards are needed - add price per unit and project cost is displayed. Helps "square up" concrete forms too. At hardware stores and home centers by Calculated Industries 1-800-854-8075 or www.calculated.com.
Concrete was used as a building material as far back as ancient Rome, and - as many of these projects are still around today - it's why we continue using it.
Done right?yours will last for ages too.
- Concrete "cures" chemically - over days - versus drying. To prevent cracking, cover with plastic or damp fabric.
- Additives strengthen, add color and/or speed cure time. Available for both pre-mixed bags and ready-mixed.
- Concrete may require added supports for strength - rebar, wire mesh, etc. Discuss project needs with a pro.
- Cement is caustic. Wear eye protection, gloves and wash off skin immediately. Do not breathe dust.
- Smooth concrete is not always best. Leave top of footings and foundations rough for better bond with mortars. Use broom to texture walks/steps for safety.
- Concrete strength is measured in PSI (pounds per square inch) indicating weight it can support or bear.
- Strength is increased by adding more cement in mix.
- Basic ready-mix is a "6 bag mix" providing 2000 PSI. For each bag added to strengthen mix: $5.00 (average).
- Weekend ready-mix delivery costs 5% to 10% more.
- Ready-mix companies allow four to five minutes for each yard delivered. After that, clock ticks at $2 per minute.
- If concrete has to be pumped from truck to site, there are additional costs and charges.
- Rather than ready-mix truck returning/disposing of order overages, plan ahead for additional use: fence posts, flag pole, stepping stones, etc. Why waste it?
- One cubic yard of ready-mix yields nine contractor-size wheelbarrows of concrete.
- Many tool rental companies offer ready-mix concrete with small minimums and reduced prices. "Spin tank" trailer you rent holds one cubic yard (must have a 3/4 ton truck or larger to haul it). Average cost: One cubic yard - $75.00, 1/2 - 65.00, 1/3 - 55.00.
Don Logay is an award-winning home improvement writer. Formerly editor-in-chief of three national professional remodeling magazines, he also created the widely quoted study for remodeling investment and return. Today Logay also writes the On The House homeowner tip series heard daily on hundreds of radio stations nationwide. Contact [email protected]
Courtesy of Calculated Industries