How are plastic water tanks moulded?

When choosing a ‘plastic’ or polyethylene water tank it is important to know which process was used to form/make the water tank.

jojo water tanks

A small rotational moulding machine

There are two moulding methods that water tank manufacturers use to make their polyethylene tanks:  conventional split-moulding and rotational moulding.  The raw material, being polyethylene granules in this case, is sourced in various grades too (also important to know when choosing a quality water tank brand).

In both cases, the polyethylene granules are placed in the moulds and heated to form the walls of the tanks. There are various proprietary processes involved; at the risk of over-simplifying the processes, the split-moulding process produces a distinct seam, usually running vertically in a continuous line all around the tank.  Rotational moulding basically ensures that once the tank is removed from the mould, there is no seam and the tank wall thickness is as even as possible.

Why is it important to know which process was used to form a poly water tank?  Have a close look at the tank and check for a seam.  If there is a seam, this is a potentially weak structural point and can be prone to cracking/splitting on cheaper plastic tanks with thin walls.  Many less expensive water tanks are made using the split-moulding process because the moulding machines are cheaper than the various rotational moulding machines and moulds.

plastic tank repair

‘Plastic welding’ can sometimes be used to repair tank splits/cracks

There are also various processing differences according to the type of rotational moulding used.  Cracks and splits can also occur in rotational-moulded water tanks, especially where the tank walls have been made as thin as possible to cut costs and where the polyethylene material has not been UV-protected.

jojo tanks

JoJo tanks are rotational moulded & UV protected

In South Africa, we recommend JoJo Tanks as this brand has been producing high quality, uV-protected ‘rotomoulded’ water tanks and chemical tanks for more than 30 years.

JoJo Tanks South Africa offer a wide range of products such as plastic water tanks and chemical tanks to suit every household, business or agricultural need, including silo tanks and silo tank stands as well as other high quality JoJo Tanks products.  See JoJo Tanks’ VERTICAL TANKS, HORIZONTAL TANKS (transporter tanks), STEEL TANK STANDS and OTHER JOJO PRODUCTS and see JoJo Tanks’ NEW 6000 LITRE UNDERGROUND TANKS. Also see our FAQ and WATER TANK PRICES.

JoJo’s superior polyethylene plastic water tanks and steel water tank stands make JoJo Tanks the leaders in plastic water tank technology and the quality, affordability and 5-year guarantee on these water tanks make JoJo products one of the best choices in South Africa.  JoJo’s water tanks and chemical tanks come standard with a number of features that are often lacking on cheaper/inferior plastic tanks made by other companies in South Africa.

We are authorised JoJo Tanks dealers in South Africa and dispatch orders directly from JoJo Tank depots to save on transport costs. Full range of JoJo Tanks products and JoJo water tanks for sale.  CONTACT US for a quote on the right JoJo water tank or other JoJo product for you.  Special discounts are available on multiple orders of chemical tanks and water tanks and to our commercial and government customers. We can usually delivery tanks and tank stands free of charge to business/commercial addresses in South Africa.


(15000 litre and 20000 litre JoJo vertical water tanks & chemical tanks are available on order directly from JoJo Tanks’ main factory)

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