Proper preparation of a water tank pad is essential for the long-term performance of your tank. A poorly constructed base can cause structural damage, leaks, or complete tank failure. This guide outlines everything you need to know to design, build, and maintain a suitable water tank pad for your tank.
General Requirements for All Pads
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Level and stable: Pads must be completely level. Sloping bases will cause water to load unevenly, resulting in eventual structural failure.
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Full support: Every section of the tank base must be supported. Unsupported areas concentrate weight, pulling the tank base away from the walls and damaging seals.
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Pad size: The pad must extend at least 100 mm further in every direction than the tank footprint.
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Materials: Only fine materials ≤ 3 mm in size (crusher dust, sand, or concrete) should be in direct contact with the tank base to prevent abrasion.
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Erosion protection: All pads must have proper edge restraint, such as timber sleepers or concrete edging, to prevent wash-out or undermining.
Remember: Any damage caused by incorrect pad preparation is not covered by warranty.
Concrete Slab (Recommended Option)
A concrete slab provides the best support for all tank sizes and is the recommended method.
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Thickness: Minimum of 100 mm throughout.
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Reinforcement: SL72 mesh as a minimum.
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Concrete strength: ~25 MPa (standard for driveways, footpaths, and house slabs).
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Curing time: Allow at least 5 days of curing before placing the tank.
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Pad dimensions: Must extend 100 mm beyond the tank in every direction.
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Load example: A full 23,000 litre tank weighs approximately 23 tonnes. The slab must be able to support this across the tank’s footprint.
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Sloping or unusual ground: Consult a concreter or engineer before pouring the slab.
Concrete Paver Pad
Concrete pavers can be used for slimline, modline, square, and round water tanks.
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Base preparation: Excavate to firm ground and level the area. Spread a sand and concrete mix at least 75 mm thick.
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Laying pavers: Lay pavers closely with gaps no greater than 5 mm. Ensure the entire tank base is supported.
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Edge restraint: Retain the perimeter with sleepers or concrete edging to prevent erosion.
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Settling: After placing the tank, fill to no more than 100 mm depth (around two ribs) for at least 48 hours to allow bedding to settle before completely filling.
Crusher Dust Pad (Round Tanks Only)
Crusher dust pads are a cost-effective option for round tanks. They must be carefully constructed to ensure long-term stability.
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Material: Blue metal/crusher dust, with a particle size of ≤ 3 mm.
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Thickness: Minimum compacted depth of 100 mm.
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Compaction: Spread evenly, compact with a plate compactor, lightly moisten with water, and compact again. The final surface should be solid and immovable underfoot.
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Pad dimensions: Must extend 100 mm beyond the tank in every direction.
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Edge restraint: Retain with treated pine sleepers (or equivalent) to prevent erosion.
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Erosion prevention: It is recommended to spread a coarse aggregate, such as 10 mm gravel, around exposed edges to protect from weather and animals.
Water Tank Stands
If using a stand:
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Structural design: The stand must be capable of supporting the tank's full weight. Consult a structural engineer if in doubt.
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Top surface: The stand’s top must be flat, smooth, and level. There must be no unsupported sections greater than 3mm for the tank's base.
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Variations: Stands can be constructed with different leg lengths to suit sloping ground, but must always present a level support surface.
Maintenance and Long-Term Care
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Inspect the pad for erosion, settlement, or undermining.
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Check border timbers or edging for deterioration and replace if required.
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For crusher dust pads, re-compact or top-up material if movement occurs.
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Keep vegetation and animal activity clear of the pad.
Warranty Reminder
Any damage to your tank caused by a base that does not meet the above requirements is not covered under warranty.
Repair costs for tank damage due to poor pad preparation can be substantial and are quoted on a case-by-case basis.