Ballast Aggregate: Building Material Guide (Plus FAQs)

What is Ballast?

Ballast is an aggregate made from a mixture of stone, gravel, and sharp sand. It is the main ingredient in general purpose concrete and is often used for landscaping jobs. It is supplied pre-blended and is ready to mix with water and cement. Ballast should contain a 2:1 ratio of stone and gravel to sharp sand.

It is heavy in comparison to other aggregates and has sharp edges that interlock to create a stronger bond than alternative concrete mixes. This makes it a durable, cost-effective, and low maintenance all-purpose building material.

This product may also be referred to as an all in one ballast and ballast mix. Although they go by different names, there is no difference between these products. However, railway ballast, on the other hand, is different and should not be used in construction projects.

What Stones and Gravel are Used in Ballast?

The stones and gravel in most ballast products include limestone, granite, gritstone, dolomite, trap rock, or quartzite. In some cases, other hard elements such as burnt clay may be included in the mix. They are normally 10mm-20mm in size.

These materials are sourced from local quarries and contain different variations of stones, so products can vary in colour, size, and shape.

Why is Sharp Sand Used in Ballast?

Sharp sand is used in ballast as it has larger grains and is heavier than regular builders’ sand. This makes the aggregate stronger and is one of the reasons why landscapers prefer it. Take a look at our sharp sand page for more information about this building material.

What is Ballast Used For?

Ballast is a durable aggregate used to create general-purpose concrete. It is most frequently used in landscaping projects due to the strength of the concrete it can produce. Common applications include:

  • Garden wall foundations
  • Patio and shed bases
  • Securing fence posts
  • Stepping stones
  • Laying slabs
  • Filling voids
  • Driveways
  • Edging
  • Paving
  • Paths
  • Kerbs

It can also be used for screeds but is perhaps not the best choice. The stones and gravel can make the concrete hard to work with. This makes it difficult to achieve the smooth finish you can make using sharp sand.

Can You Use Ballast as a Sub Base?

While you can use ballast as a sub-base, many tradespeople prefer to use MOT Type 1, which includes a wider range of sand, stone, and gravel. The variety in aggregate size creates a more compact layer for you to pour concrete onto. This improves the base’s structural properties and is ideal for commercial usage.

How Much Does Ballast Cost?

On average, ballast from builders’ merchants costs £0.17 per kg when buying a 25kg bag and £0.08 per kg when buying an 800kg bulk bag. This figure is based on retail prices and includes VAT. To get better prices, sign up for a trade account with your chosen merchant before buying.

Price also depends on the quantities you are purchasing. Try to buy in bulk when possible, which will give you a better position to negotiate. When choosing which supplier to use, remember to factor in delivery costs if you are making a decision based solely on price.

Are Some Ballast Mixes Better Than Others?

Yes, some mixes will perform better than others. The best will include stones and gravel in a wider range of sizes and shapes, which will prevent gaps in your concrete mix. It is also important that the ballast contains the correct ready-mixed 2:1 ratio of stones and gravel to sharp sand.

Apart from the contents of the product, the quality of the packaging can make a difference. Cheap and thin packaging may split when carried across site, making transporting the materials harder.

It may also be the case that the packaging has been split before you bought the product and is wet. This would increase the moisture content of your ballast and may make the concrete runny if you do not adjust the amount of water you add to your mix.

When supplying in bulk, good builders merchants will provide a consistent volume in their dumpy bags. However, when using less professional suppliers, you may notice that the bag fill volume varies significantly, leaving you with too little, or too much.

Should You Cover Bulk Bags of Ballast?

There is no need to cover bulk bags of ballast if it is raining, aggregates are stored outside at most merchants. Although it will get damp, you will be adding water to the aggregate when making concrete anyway. Simply reduce the amount of water you add to your mixture if you are using a wet aggregate.

If it is particularly windy, you may want to cover your bags with a dust sheet to minimise the amount of dust generated. You could also wet the mixture at the top of the bag to stop airborne dust.

Is Ballast Environmentally Friendly?

Ballast is an environmentally friendly building material. It is created using naturally abundant rock and is often made up of broken stones from previously completed construction projects. Tarmac’s product data sheet confirms there are no adverse environmental effects if the product is used as intended.

Ballast to Cement Ratio

Typically you will require six bags of ballast for every one bag of cement. This 6:1 ratio will achieve a concrete that is Grade C20 / Gen 3 and has a strength of 20 Newtons after 28 days. C20 concrete is the most common grade and is suitable for the majority of general building work including shed and garage wall foundations.

A higher grade will be required for house building and commercial projects. Using an 8:1 ratio would result in concrete suitable for foundations.

How Many Shovels are There in a Bag of Ballast?

There are 4-6 shovels in a 25kg bag. How many shovels you will get out of a bag depends on how high you pile the ballast. Heaped and levelled shovels vary in weight. This makes it hard to give a one-size-fits-all answer.

Using these calculations, there will be between 128-192 shovels in a bulk bag. If you were to get five shovels from a 25kg bag, you would get 160 shovels from an 800kg bulk bag.

To calculate how many you will get from a bulk bag, take the number of shovels you get from a 25kg bag and multiply this by 32. This will give you an accurate number for an 800kg bag, based on your experience.

How Much Cement for One Tonne of Ballast?

You will need 166kg of cement for one tonne/1000kg of ballast. This calculation uses a 6:1 ballast to cement ratio and will produce C20 grade concrete. If using 25kg cement bags, you will require 6.67 bags.

How Much Ballast Do You Need?

Using a 6:1 ratio of ballast to cement, you will need 1,500kg to create one m3 of concrete. The amount you need will vary depending on your surface area, the thickness of your base, and your preferred mix ratio. 

This equates to 60 bags of 25kg ballast or 1.88 bulk bags, which contain approximately 800kg, and 10 bags of 25kg cement. To be on the safe side, driveways, patios, and shed bases should have a concrete base at least 100mm deep.

How Many Bags of Cement to a Bulk Bag of Ballast?

Using a 6:1 ballast to cement ratio, you will need 5.33 bags of 25kg cement for a 800kg bulk bag. This will give you 133kg cement to mix with 800kg of ballast.

Related Posts

How Many Bags of Ballast in a Bulk Bag?
Building Sand
Horticultural Sand
Kiln Dried Sand