Building Storage Tanks

In general, you should work with an engineer or someone who has experience designing and building storage tanks. 

Here are some photos of the construction of a octagonal deposit tank built by a fellow volunteer.  While the shape of the deposit tank can vary, the following photos are a great overview of formwork and the construction process.

	Clear the construction area of debris.  Make sure the area is level.
	Pour the foundation slab.  Dig away along the perimeter of the foundation to create a “key” where the slab will be slightly thicker.
	Pour the foundation slab with your rebar that will be used to reinforce the sides of the tank.  Using rebar, you can tie a horizontal piece to align/true the vertical pieces of rebar exiting the foundation.
	Use posts to stake the formwork.  Make sure the posts are strong enough and embedded deep enough to keep formwork in place under the pressure of the concrete poured into the form.
	Internal supports can be used to align formwork and ensure that the formwork stays in place during the first pour.
	Using boards as shown helps keep even spacing of your form to ensure an even wall thickness throughout the structure.
	The formwork from the first pour can be reused in a “lift” for the second pour.  The second pour should be made as soon as the first pour sets (1-2 days) so that the concrete from the second pour bonds to the concrete of the first pour.
	Use posts to keep the form elevated. Sand bags can be used to anchor the posts in place.
	Add a coat of plaster mix (1 part cement to 3 parts sand) to the tank walls.  A smooth coat on the inside and outside will reduce future organic growth on the walls.
	Setup the formwork table for the ceiling concrete slab.
	Posts are used to support the table form and are removed after the ceiling slab has set.
	Rebar layout to tie the slab to the rest of the tank structure and provide reinforcement to span the unsupported distance of the ceiling.  A form is used to provide an access door to the inside of the tank for future cleaning and maintenance.

Here are some photos of additional tank features worth considering.

	Here is an example of a built in ladder and hand hold as part of the tank structure.
	The tank should have an access hole from the top for cleaning and maintenance. The weight of the lid alone should deter children from tampering with the system
	The tank should have an inlet, overflow, exhaust vent, outlet, and cleanout (not shown). Note: This tank contains two chambers so there is redundant pipework. This tank also needs to be cleaned and painted.