Brick et al a multi-faceted indigenous construction company, establishes strong expertise providing quality construction and environmental solutions. Our team comprises of qualified Built environment practitioners.

Just as the year 2019 gradually winds down, it goes down in our annals as a company challenging and eventful, we will like to share our construction experience on septic tank in a water logged (reclaimed land) area of Lagos state, Banana Island Estate to be precise.


Banana Island estate operates a central sewage system but for emergency/ system breakdown/ maintenance property owners are encouraged have back up sewage system in thier facility. Each facility has a sewer collection point which empties into the estate sewer mains.

We are not able to secure permission to upload structural and mechanical drawings as they classified inputs of the Services and Structural Engineers.

To construction a sepetc tank ( 3m height) in this environment, it has to be precast i.e cast and sink. Water level is relatively high, 3 feet excavation below the ground, you have to be prepared to battle water to achieve task.

The methodology is to cast walls of the septic tank to the required height on the ground surface without the floor, only starter rebars for floor.

Most times, its ideal to have the internal formwork in place and place the rebar around then place external formwork. The challenge with this procedure is the placing of reinforcement for the floor, we want a monolithic structure and avoid voids. For this project we employed both techniques to be double sure we achieving a water tight and monolithic structure.

The internal formwork was formed then after the rebars and water stopper are placed the fromwork was carefully deformed. The floor starter rebar was placed then internal and external formwork replaced with a 2x4 wood placed on the internal (at the buttom)to form groove.

The formwork both internal and external requires adequate strut, the consequences of this as a contractor is fatal if formwork fails while pouring concrete.

The concrete has to be grade 30, because the structure is below the ground mix with the a very good sealant (penetron was used here) and well vibrated.

Then after deforming the formwork, the sepetic tank will be plastered in and out with sealant in mix.