How to Construct a Concrete Pond
Estmating the materils
Excavating
To drain or not to drain
Placing the forms
>Working with Concrete
Pouring the Floor
Setting
Fountains and Spouts
Use only Portland cement. Buy a clean, well-graded sand with particles which range from 1/8-inch coarseness down to fine. This varied particle size will give you a stronger, denser concrete than sand which is all coarse or all fine. Dusty sand makes weak concrete that sets poorly. Use crushed stone or pebbles that are free of foreign matter.
Concrete mixes which make use of bank-run gravel seldom are satisfactory, principally because the sand and gravel are not in proper proportion. Usually there is too much sand in the natural mixture as it is taken from the gravel bank, and that produces an overporous concrete. It can be used, however, by separating the sand and gravel by screening, and then adding each in proper proportion.
The best concrete mixture for ponds consists of one part cement, two parts sand, and three of gravel. If the sand and pebbles are bone dry, a one-sack batch of concrete (all a man can mix really thoroughly at one time) will require 5 1/2 gallons of water. Use only water that is clean enough to drink. If the sand and pebbles are damp (damp enough to be formed into a ball of sand in your hand) use 4 1/2 gallons. If they are wet, use 3 1/2 gallons. It is far better to underestimate the amount of water, and then add a little more at a time until you get a workable mixture, than it is to overestimate. If the mixture is soupy, it contains too much water. It will set, and might even hold up well enough, but certainly not as well as it would if mixed with the proper amount of water. Too much water dilutes the cement paste and weakens its bonding qualities.
In the interests of precise measuring, you will do well to make advance preparations. A sack of cement is exactly 1 cubic foot. Construct a bottomless box (see Drawing 11) with a capacity of 1 cubic foot, and use it for measuring the sand and gravel. Mark a bucket so you can measure gallons, half gallons, and quarts in it.
Concrete can be mixed on any cemented surface, such as a garage floor or driveway, but must be hosed off before it has a chance to set. If such a surface is not available, you will have to construct a wooden platform of boards with edges straight enough to form a fairly watertight surface. The Portland Cement Association recommends a platform 7 feet wide and 12 feet long as being large enough for two men to work on simultaneously. Run a railing 4 or 5 inches high around three sides of the platform so materials won't be lost while they are being mixed.
Start early on the day that you mix and pour the concrete, for to be watertight a pond shell should be completed in one continuous operation. To do the job well and to enjoy it as you go, you should have at least one husky helper. While one of you shovels concrete into the forms, the other can be mixing a new batch.
Measure out 2 cubic feet of sand on the platform, make a nest of it, and pour in one bag of cement. With a square-ended shovel, turn the mixture over and over until it is well blended, showing no streaks of discoloration. Flatten the pile, cover it with 3 cubic feet of gravel, and continue mixing until gravel, sand, and cement are all distributed evenly.
Pour water into the mixture slowly while your helper continues to mix. The mixing is finished when the full measure of water is combined evenly with the solid ingredients. A good mixture is one soft enough to tamp easily into place in the forms, yet stiff enough to hold the marks when you scratch it with a trowel or shovel.