Things You'll Need
Shovel or mechanical auger
10 penny nails
2-by-4-inch boards, 3
All hydraulic cements cure underwater, including Quikrete. A common misconception about concrete is that the curing process is dependent upon water evaporation. For non-hydraulic cements--those that use lime and gypsum plaster as a binder--this is true, but contemporary builders only use these cements for special projects such as historical restoration. Modern cement binders allow builders to pour concrete underwater and leave it to cure. As a result, pouring concrete underwater around a post is simple.
Measure the length of the pole. Dig a hole with a depth equal to 20 percent of the length of the pole. The top of the hole is the first layer of solid ground. Do not consider sediment part of the hole depth. For example, if you have 6 inches of sand above the bedrock and the hole required is 29 inches--for a 12 foot pole--the digging depth is 35 inches.
Put the pole in the hole. Hammer three 2-by 4-inch leg boards to the pole for triangulated support. Adjust each support closer to the hole or farther away to straighten the pole vertically. Check the plumb of the pole with a bubble level. Once the pole is straight, pour the Quikrete.
Pour the concrete into the hole using one of three methods. If the water is static or only has a light current, open the Quikrete bag, hold the opening closed, lower the bag into the water and release the concrete just above the hole. If there is a current, you have two options. First, simply place the bag of concrete in the hole around the post. The water saturates the bag and cement and the concrete cures. Secondly, use a tremie. A tremie is a pipe with a funnel at the top. Place the tremie in the hole. Pour the Quikrete into the funnel and spread the concrete around the hole as it spills out the bottom of the tremie..
Allow the concrete to cure before removing the 2-by-4-inch legs. Quikrete requires three days to cure underwater. If you simply put the bags around the post and allow the water to saturate the cement, leave the legs up for one week to ensure that the concrete sets.
Ryan Hotchkiss began writing professionally for a local newspaper while in college. He graduated with a bachelor's degree in English composition, then worked for five years at an online education company. Hotchkiss continued his writing career composing bid proposals for an architecture firm until moving to Costa Rica.