The old saying "good fences make good neighbors" isn't always true, but a well-set fence keeps children and pets safely in the yard. Set the fence posts using a quick-set post concrete or a standard concrete mix to ensure a sturdy installation. While quick-setting concrete sets in as little as four hours, allow at least 24 to 48 hours for a standard concrete mix to dry, especially if the weather is cold and/or wet.
Drying times vary according to the concrete mix and weather conditions, ranging from four hours to 48 hours or more. Curing time is the amount of time it takes for the concrete to reach its full strength, generally 30 days.
Quick-Set Post Concrete
A quick-set post concrete, such as Sakrete or Quikrete Fast-Setting Concrete Mix, allows you to add the fence panels approximately four hours after setting the posts. In general, the post hole should be three times the width of the post. A 4x4 fence post needs a 12-inch-diameter hole. The depth of the hole should be 1/2 to 1/3 of the above-ground height of the post plus 4 to 6 inches to allow for a gravel base.
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Add 6 inches of gravel to the hole and compact it using the end of the post or a 2x4 board. Add the post and make sure it is plumb with a spirit level. Then, depending on the manufacturer's instructions, either add the dry Quikrete mix or fill the hole 1/3 full of water and then add the Sakrete mix. Slowly add 1 gallon of water for each bag of Quikrete mix and allow it to soak into the dry mix.
Adjust the post as needed to ensure it is still vertical and hold it in place for three to five minutes. Quickly smooth the top of the concrete before it sets so it slopes away from the post, which will allow water to flow away from the wood or metal post. The quick-set post concrete will allow you to start adding fence panels in approximately four hours.
Standard Concrete Mix
While quick-setting concrete mixes are one solution to setting fence posts and other concrete projects, they also add to the cost of your project. Other types of concrete mixes are slower to set and cure but are less expensive, so if budget is an issue, they work just as well as a quick-set post concrete mix. Prepare the post holes and then mix the concrete and recommended amount of water per the package directions in a cement mixer or wheelbarrow.
Place the posts in the holes, centered and plumb. Brace with scrap lumber so the posts don't move while adding the concrete and during the drying time. Pour the wet concrete into the hole, working your way around the post. Use a shovel, scrap lumber, or other tool in an up-and-down motion in the wet concrete to release air bubbles and mix the concrete in the hole.
Add the concrete until the hole is full and then smooth the top so it slopes away from the post. Double-check the plumb to ensure the post is still vertical. Allow the concrete to dry for at least 24 hours and preferably 48 hours before adding fence panels.
Drying Times and Adverse Weather
Concrete drying times vary according to the temperature and moisture content of the soil. In general, concrete should be prepared and poured when temperatures are between 50 and 85 degrees Fahrenheit. On hot days, work in the morning when temperatures are cooler and use cold water in the mix. When temperatures are cold, use hot water in the mix. Avoid installing concrete when the ground is frozen because if the water freezes in the mix, it will weaken the final product.
If the soil is extremely dry, fill the post holes with water and allow it to soak into the soil before adding the posts and concrete. In addition, fast-setting mixes can be premixed and poured into the post holes to ensure that an adequate amount of water is mixed with the concrete. If the ground is boggy or the hole fills with water as you dig, you can pump the water out of the hole, adjust the amount of water in the mix to accommodate the excess water, and/or consider waiting until the weather improves and the soil dries out. Alternatively, line each hole with plastic sheeting before installing the post and concrete.
While the concrete is usually dry enough to install the fence panels in four to 48 hours, it needs additional time to finish curing and reach its full strength. Depending on the concrete product used, it can take up to 30 days.