Apart from the careful selection of the size and shape of your tank, one of the most important factors in the installation of a rainwater tank is the preparation of the base.
Types of Bases Suitable for Poly Water Tanks
For poly tanks, the most suitable base must be a solid, flat surface. Your manufacturer will be able to provide recommendations, but generally, the best options are bases made of concrete or boxed compacted crusher dust.
“Crusher dust” is available from nursery suppliers and is a mix of small crushed rock and fines. When compacted it binds together tightly creating a strong, stable surface for placing your tank. The crusher dust must be boxed in with some retaining structure (e.g. retaining beams, bricks) to prevent it from washing away over time.
Concrete is the best base for a slimline tank because the shape of the tank (tall and narrow) means a risk of the tank tipping over if not on a solid base.
Tank stands are another option for the tank base but must be strong enough to hold the weight of the tank when full. Use hardwood decking with gaps no greater than 10mm.
Regardless of the materials you choose, the ground must be compacted before laying the concrete or crusher dust, and the base must be carefully laid and finished to ensure it is flat and level.
Given the importance of the finished base, it may be worth considering getting help from someone experienced in concreting to ensure you get the base right. Alternatively, if you’re using crusher dust it is vital you use appropriate compacting equipment to get the best result.
Types of Bases to Avoid for Poly Water Tanks
An unsound base or an eroding base may void your poly tank manufacturer’s warranty.
Take care to avoid the following:
- Rocky and uneven ground with little preparation causes under-mining of the base of the tank and sharp objects can protrude through.
- Bricks or timber sleepers, like these, can move or erode over time.
- Corrugated iron decking should never be used as it is unstable and may stress the tank and cause the tank to fail.
You should also take the time to ensure there are no tree roots that are likely to intrude on your tank’s base area over time.
Do I need to leave space around my tank base?
Yes, a larger base provides stronger foundations and reduces the risk of erosion and the foundation slipping. If your foundations are poor, then your tank warranty can be compromised and/or your tank ruined under the weight of a full tank of water.
How much space should you leave?
- If you are installing a slimline poly tank, then a 100mm space around each side of the tank is normally sufficient.
- For round poly tanks, the base should be at least 500mm greater than the tank diameter.
Most importantly, always follow your manufacturers’ instructions to ensure you meet the warranty requirements.
National Poly Industries has detailed instructions for preparing your base and installing your water tank. If you have any further questions, contact our friendly team today.