How much does it cost to pour a 20x30 concrete slab?

How much will it cost to pour a 20x30 slab of concrete? Concrete costs $4–$8 per square foot on average. This means a 20-by-30 foot concrete slab will cost $2,400–$4,800 depending on the slab's thickness and the type of concrete needed.

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Slab size and thickness aren’t the only variables that affect cost. Here are some other factors to consider while budgeting.

Concrete Grade

Concrete isn’t a single material; it’s a mixture of cement, water, and an aggregate material such as sand or gravel. The strength of concrete, also called its grade, depends on the ratio of these ingredients and is measured with numbers ranging from M5 to M70. Concrete mix with a grade of M10 to M25 is typically strong enough for residential use and less expensive than higher grades. (Higher numbers are used in large-scale commercial projects). The word “grade” can also refer to concrete poured over an incline, like for a driveway that goes up a hill. A concrete contractor may charge more if the incline is steep since working with heavy machinery on a slope can be difficult. Your cost will also be higher if the ground grade needs to be increased or lowered before pouring the concrete.

Finish

Concrete is quite versatile. It can be stained, stamped, or sealed to create a variety of appearances, though this will cost more than pouring basic concrete. Stain or dye to change the concrete’s color costs an additional $3.50–$7.50 per square foot. Stamping a design such as tiles or cobblestones into the wet concrete costs $10–$14 per square foot, though more elaborate designs and engraving can cost $18–$20 per square foot. A smooth epoxy finish or a weather-resistant concrete sealer will each add about $4.50 per square foot.

Labor

The $4–$8 per square foot average usually includes professional labor at about $50 per hour. However, some projects require extra labor. For example, if you’re replacing an old concrete pad, it will need to be demolished and removed before the new concrete is poured. This can cost anywhere from $500–$1,800. You may also need to hire a pump truck for about $900 if the concrete needs to be poured in an area that’s difficult to access.

Landscaping Costs

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Depending on how much your new concrete slab will change your yard’s layout, you may need to hire a landscaping service to move or replace trees, shrubs, or turf. Many landscapers can also change the incline of the subgrade soil surface if necessary. These services can cost up to $200 per hour for design and implementation.

Reinforcement Materials

Additional materials are usually needed for slabs that hold a great deal of weight, particularly concrete foundations. Wire mesh ($0.35 per square foot) and steel rebar ($2–$3 per square foot) both add strength, particularly when the ground underneath the concrete is poor. Additionally, some home improvement projects require reinforced concrete slabs with thicker edges that can hold more weight. These edges add $1–$2 per square foot. Chemical additives also increase the strength of the concrete mixture itself. Finally, house foundation costs are higher than other concrete slab projects because most require a 2-inch styrofoam under-slab insulation layer at the cost of $0.50– $2 per square foot. Adding a vapor barrier to keep moisture out is also a good idea, which adds about $0.50 per square foot.

Repair vs. Replacement

Concrete is a highly durable material that can expand and contract with changing temperatures, but excessive weight, shifting soil, and obstacles such as tree roots can create cracks over time. It may be possible to repair an existing concrete slab in some cases. For example, a driveway or walkway with cracks or chips in only the top layer can sometimes be resurfaced rather than entirely replaced. Cracks may cost between $500 and $2,500 to repair, and driveway resurfacing can cost anywhere from $1–$10 per square foot.