Sand vs Rock - What's the Best Material for My Tank Base?

So, you’re installing a water tank on your property, and you’re wondering what’s the best type of base material, right? Over the years you’ve seen a few different materials used for tank bases, but you’re not sure what’s going to be most serviceable?

Preparing the base for your tank is one of the most important stages of the installation process. And it’s one that you need to get right first-time round. That’s why we’ve taken the time to list out some of the common materials that are used for tank bases, and the pros and cons of each material.

Why Do I Need to Prepare a Tank Base?

When your rainwater tank is full, it’ll be extremely heavy and it’s important that the ground underneath it is stable enough to support this weight. Failure to prepare the area suitably will inevitably result in costly repairs and safety issues down the track.

It’s important to note that when it rains, a certain amount of water will run off the roof of your tank, down the sides and onto the base. Ideally, the material you choose for your tank base will drain well so that it doesn’t stay so damp underneath the tank 24/7.

Regardless of the material you choose for your tank base, the area must be clean, level and well compacted.

Some of the base materials work well for poly tanks can cause rusting issues with steel tanks. So let’s zoom in and have a closer look at some good options for tank bases, and a few that aren’t so good:

1. Fine Crushed Rock

Of all the base materials, this is our top pick. 7mm crushed blue metal or something similar is ideal because:

• • It drains well - crushed rock will drain water away from underneath your tank, and this is important, especially if yours is a metal tank.
  • It levels but doesn’t compact too much - having a material that will level to a nice, even base is essential because once your water tank is full, it will be very heavy.
  • It’s budget friendly - crushed rock is readily available from most garden centers and landscaping supply companies, and it’s reasonably cheap too.
  • Looks great - because stone won’t degrade over time, it always looks great.

Installing a retainer of some sort might make it easier to get your rock base level, and it will also prevent any gravel from washing out from around the edges of your base when it rains.

Ensure that your crushed rock base is well compacted and at least 75mm thick.

2. Concrete

If yours is a poly tank, you can’t go past concrete for a base material: it looks tidy and neat, is durable and, if done correctly, will provide a level, super stable base. Your concrete base should be a minimum of 100mm thick.

However, if yours is a steel tank, concrete is less than ideal because moisture under the tank won’t drain away, which will eventually cause damage to the base of the tank.

3. Sand

It’s cheap. It’s easy to source. It’s easy to level. They’re about the only positive things to say about sand tank bases.

Although installing a retainer can help to maintain a sand base to some extent, as a base material, it’s not a good choice for several reasons:

• • It stays damp - if your tank is a steel one, this will eventually affect the steel base of your tank
  • It washes out - in a torrential downpour, water running down the sides of the tank will wash the sand out from around the sides and the underneath of your tank. This can make the tank unstable, and in a worst-case scenario, the tank could eventually topple over.
  • Children love to play in it - kids, toy diggers, spades, and buckets… the sand around the tank is an ideal place to play, but not a safe one. Digging out around the tank will cause it to be unstable and could cause it to topple (this is a real safety issue, especially if yours is the taller slimline design).
  • Rodents - rats and mice will tunnel through the sand underneath your water tank, causing it to become unstable. Unfortunately, this can be an issue that’s not realized until it’s too late because their work mightn’t always be obvious immediately.

4. Pavers

Concrete pavers are not a good choice for your tank base because they don’t provide a solid surface, and they’re apt to move over time, which will undermine the stability of your water tank.

5. Dirt or Clay

A dirt or clay base isn’t advisable because, like sand, dirt/clay will erode during heavy rainfall and is likely to become a haven for burrowing animals.

Building a Retainer

Depending on the fall of your land and the type of material you choose for your tank base, a retaining framework may be necessary to create a level, well compacted area.

Wondering what to use? Treated pine sleepers, bricks or concrete masonry blocks are often used to construct the framework for tank base retainers and are all great options for the average DIYer.

Maintaining Your Tank Base

Keeping your tank base in good order will help to prolong the life of your tank.

Ensure that your plumbing is kept in good condition. Regularly check for leaking pipes or loose connections in the inflow and outflow pipes which could cause extra water to flow down the side of the tank and wash out the base material.

If you notice the presence of burrowing rodents, deal with them immediately.

Don’t allow children or pets to dig around the tank.

As they say, ‘prevention is better than cure’ - taking the time to prepare and maintain your tank base will save you a pretty penny in tank repairs in the long run. Considering your water storage is a long-term investment, it’s worth going the extra mile to ensure that it’s safe, sturdy and built to last.