How to Slope a Concrete Patio for Drainage

A concrete backyard patio with partial cover.
What You'll Need
Tape measure
Wood supports
Concrete mix
Concrete knife
Eye Protection
Protective clothing

When planning a concrete patio construction project, one of the most important things to keep in mind is that your patio will inevitably have water buildup during periods of rainy and snowy weather. If that water stays on your patio surface it will cause damage to the structure of the concrete itself and may form a breeding ground for mosquitoes and mold. Thus, it is crucial that you plan on providing a method for the concrete patio to drain the excess water that collects on top.

Ideally, this water should drain off of the patio and away from the foundation of your home, where it can help to water your grass or the plants in your garden. Sloping your patio properly will ensure that the concrete surface has the proper drainage capability.

Gather Your Materials

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The materials that you'll need for this project depend somewhat on your patio and the state you reside in. If you haven't yet built a patio and are considering how to account for drainage in your construction plans, you may not need all of them. However, if you've already built a patio but have not allowed for proper drainage, and your existing patio does not drain adequately, make sure you purchase everything listed in the materials section.

Calculate the Ideal Slope

The standard formula for the slope of a concrete patio is a 1/4-inch drop for every foot of length. If the slope is more gradual than this, you may run into trouble getting water to run off properly. Slopes that are steeper than this are fine, but you may also wish to consider the ease of mobility on a concrete patio that is too steep. This is a matter of personal preference and is also dependent upon the shape and overall design you're using.

In order to calculate the necessary slope for your patio, measure the length across in feet, starting where the patio meets your house. Then, multiply the measurement by 1/4 in order to find the number of inches in elevation that the two edges of the patio should differ by.

Mix and Lay Concrete

Follow the instructions on your product and mix your concrete in a wheelbarrow. If you need to add a slope to a previously built concrete platform, you should still use wooden forms, like 2x4s, in order to make sure that the concrete lays evenly. Dig out the edges alongside your patio, and pound these into place. Set another support at the edge of the area you need to add concrete to as well. Pour the mixture gradually into the mold that you've made, and allow it to begin to set before removing the supports. As you're troweling it smooth, try to make the blend between the new and old concrete seamless. For additional assistance in laying a new concrete patio, consult with an expert at a local home improvement center or related store.

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