An all-in mix of sharp sand and gravel graded from dust to 20mm, blended ready for site-mixed concrete. Mix it at 1 part cement to 6 parts ballast for wall footings, garden steps and setting fence posts.

Ballast is a concrete mix, not a sub-base. For a path, patio, shed base or driveway, lay and compact MOT Type 1 instead.

concrete for wall footings
concrete for garden steps
setting fence posts and gate posts

Ballast

Price range: £124.00 through £166.00 inc. VAT

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Quantity	20 x 20kg Mini Bags, 40 x 20kg Mini Bags, 850kg Bulk Bag

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Specifications, Inspirational Ideas & DIY Guides

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Why Professionals & Homeowners Choose, Applications, Inspirational Ideas, Maintenance, Purchasing Tips, FAQs, Related Products

Overview

Ballast is the aggregate people buy without knowing what is actually in the bag, and it is worth clearing that up before you order. It is an all-in mix, sharp sand and gravel already blended and graded from dust up to 20mm, so if you add cement and water and you have concrete. The stone is usually rounded river or marine gravel rather than crushed rock and close to half the bag is sand. What matters more is that ballast has two lives that behave in opposite ways. Spread loose and compacted it is free-draining. Mix it with cement and it is impermeable. Two very different animals, and most of what people get wrong about ballast comes from treating them as one.

Why Professionals & Homeowners Choose Ballast

Ballast removes a decision: the sand and the stone arrive already blended, in roughly the proportions a general-purpose concrete wants.

One bag does two jobs, so you are not ordering sharp sand and 20mm gravel separately and guessing the ratio yourself.
Mixed at 1 part cement to 6 parts ballast it gives around 20 N/mm² at 28 days, the standard domestic strength for garden concrete.
The mix turns easily under a shovel, so hand-mixing in a barrow or small mixer stays a one-person job.
It compacts well enough to stand in as a sub-base where crushed rock is expensive to deliver, which is how it became the default across the aggregate-poor south-east.
Nobody controls the fines ratio in a ballast and you cannot see it until the bag is open, so I would not use it where the concrete has to hit a specified strength.
Water passes through compacted ballast rather than sitting on it, but far more slowly than through clean washed stone, so it is not what goes in a French drain or a soakaway.

Ballast Applications

Nearly every use for ballast is buried and what ballast is not is a surface: not a decorative gravel, not a mortar sand, not a drainage fill.

General-purpose concrete at 1:6 for shed bases, wall footings, step and path foundations, and haunching behind edging.
Setting fence and gate posts, where one barrow of 1:6 per post does the job.
Bedding kerbs and edge courses, mixed semi-dry so the units stay where you tap them.
A 10 to 15cm binding layer over coarse hardcore on a path, stopping the big stuff underneath migrating up through the gravel, with a skim of sharp sand worked into the top to give the surface stone something to bed into.
A sub-base under a patio or light path at 100mm compacted. Under a driveway I would still order MOT Type 1 at 150mm.
Backfilling trenches and voids in 150 to 200mm compacted lifts, where soft clay or topsoil would settle on you later.

DIY Guides & Inspirational Ideas

Laying Paving Slabs on Dry Mix: Ratio, Depth and Method

I cover the reasons so many DIY patios come loose in their first month.

Ben Parrot

What Is a Sub-Base? Depths, Materials and How Much to Order

This is the foundation of every path, driveway and patio I've ever laid.

Ben Parrot

How to Lay a Gravel Path That Won’t Sink, Soften or Spread

Thin gravel on a firm base over deep gravel always. How I build one that looks new after ten years.

Ben Parrot

Ballast Maintenance

Ballast needs no maintenance once it is buried, so the upkeep belongs to whatever you built with it. Concrete mixed from it reaches design strength at 28 days, so keep a new shed base clear of anything heavy for the first month, however solid it feels after a day. On paving over a ballast base, sand joints settle and want topping up at about four weeks, then monthly for four to six months. Keep the pressure washer off it for those three months, or you will blast the jointing straight back out.

Purchasing Tips

An 850kg bulk bag of ballast is roughly half a cubic metre, which mixes about half a cubic metre of concrete or spreads about 5m² at 100mm loose. The calculator on this page does the sum, or divide your cubic metres by 0.5. A 3m by 2m shed base at 100mm is 0.6m³, so two bulk bags with a bit spare, plus five to seven 25kg bags of cement. For sub-base work add about 30%, because it loses depth once it’s been compacted. Wear gloves when handling because wet cement burns skin.

If you would rather talk your ballast order through with a person, ring Outdoor Aggregates on 0330 043 7585. The office is open 7am to 7pm, seven days a week.

FAQs

What is ballast used for?

Ballast is used for site-mixed concrete and as a bedding and backfill aggregate: shed bases, fence posts, wall footings, path foundations and haunching behind edging.

What is the mix ratio for ballast and cement?

The standard domestic mix is 1 part cement to 6 parts ballast, giving around 20 N/mm² at 28 days. Tighten it to 1:5 where the concrete carries a car.

How much concrete does a bulk bag of ballast make?

One 850kg bulk bag of ballast makes roughly half a cubic metre of concrete at 1:6, which is a 3m by 2m slab at about 80mm.

Can you use ballast as a sub-base?

Ballast works as a sub-base under patios and light-use paths at 100mm compacted. MOT Type 1 is graded to a proper spec and packs tighter, so it is what I use, especially under a vehicle.

Is ballast the same as sharp sand?

Ballast is not the same as sharp sand: it is sharp sand already blended with gravel up to 20mm, so about half of what you tip out is stone.

Can ballast be used for drainage?

Ballast is free-draining as a loose compacted layer, so water passes through it rather than pooling on it. It is still the wrong fill for a French drain or a soakaway, because its sand and fines choke the voids those rely on. Mixed into concrete it stops draining altogether, since the sand fills the voids that would have carried the water.

Ballast

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