All-In Ballast: The Pre-Blended Aggregate for Site-Mixed Concrete

A homeowner orders 8 bulk bags of all-in ballast for a workshop base. Their builder turns up, takes one look at the bags, and says "that's the wrong stuff, mate, I asked for sharp sand and twenty mil." Both products have grey, gritty material in them. Both come from the same builders' merchant. They are not interchangeable. The 8 bags get put back on the truck, the day's work is lost, and the homeowner pays a restocking fee. The confusion between ballast, sharp sand, and coarse aggregate is one of the most common ordering mistakes in domestic groundwork, and one of the most avoidable.

What it is and what it's for

All-in ballast is a pre-blended mixture of sharp sand and coarse aggregate (gravel), sold as a single product so you can mix concrete without buying the two ingredients separately. It's a convenience product. The composition under BS EN 12620 (the current European standard for concrete aggregates, which replaced the old BS 882 on 1 January 2004) is roughly 40-70% gravel of 10-20mm size and 30-60% sharp sand, with a maximum 5% fines. Most merchant-supplied ballast is somewhere near 50:50 by volume, though the standard allows variation either side.

It exists for one reason: site-mixing concrete with a single bag of aggregate is faster than measuring out separate sand and gravel. You add cement, water, and ballast in a fixed ratio, run the mixer, and pour. That's why it dominates domestic shed bases, fence post concreting, small footings, and any job where 1-3m³ of concrete is needed and ready-mix isn't practical.

Three things ballast is not:

It's not sharp sand. Sharp sand is the fine 0-4mm fraction only. Use it for floor screeds, mortar, or the sand component of a separately mixed concrete. Mix sharp sand with cement and water and you get mortar, not concrete. The mix has no gravel and won't reach concrete strength.

It's not coarse aggregate. Coarse aggregate is the gravel-only fraction, typically 10mm or 20mm shingle. Use it for drainage, soakaways, sub-base under slabs, or as the gravel component of separately mixed concrete. Mix coarse aggregate with cement and you get a harsh, dusty mess with no fines to fill the voids between stones.

It's not hardcore. Hardcore is crushed brick, concrete, or MOT Type 1, used for the compacted base layer beneath a slab. Hardcore goes under concrete. Ballast becomes concrete.

What "ballast" actually contains

The composition matters because it explains what ballast can and can't do. A typical bag of 20mm all-in ballast contains particles ranging from dust-fine sand grains up to 20mm rounded gravel. The full grading range is what makes it work as concrete aggregate: the fine particles fill the voids between the gravel, the cement paste binds everything together, and the result is a dense, strong material with no internal voids.

Buy 20mm gravel and sharp sand separately, dump them in the mixer in equal volumes, and the result is poor. The reason is the gap in particle sizes between 4mm sand and 10mm gravel. Nothing fills it. As one BuildHub member put it, "you don't actually want to have sand and 20mm gravel with nothing in between." All-in ballast solves that problem because the supplier has graded the mix across the full 0-20mm range, so every particle size has a partner.

Colour and texture vary by region. Yellow ballast is common in South-West England where the local quarries produce iron-stained aggregate. Grey or mixed-colour ballast is more typical in the South East, Midlands, and North. The colour is cosmetic; structurally any BS EN 12620-compliant ballast performs the same. If you're concreting under a slab where the colour is invisible, take whatever your local merchant stocks. If you're doing exposed concrete (a path, a step, a polished slab), order in one batch from one supplier so the colour stays consistent.

All-in ballast vs coarse aggregate vs sharp sand

These three products sit on the merchant's price list right next to each other. The names get used loosely in conversation. Here's what each one actually is, and what it's for.

The simplest mental model: ballast is the all-in-one pre-blend, sharp sand is the fine half on its own, and coarse aggregate is the coarse half on its own. You can replicate ballast by mixing sharp sand and coarse aggregate yourself in roughly 50:50 by volume, but for domestic work it's almost never worth the bother. Bulk-bagged ballast is cheaper than buying both ingredients separately, and the gradation across the full size range is more reliable than what you'll achieve with a shovel.

Mix ratios and the great 1:5/1:6/1:8 confusion

This is where homeowners get tangled up, and where the published advice across the web actively contradicts itself. The confusion has three sources: different ratios serve different applications, different sources quote different "standard" numbers, and one persistent piece of consumer-guide misinformation tells people to use 1:8 ballast:cement for foundations. That last one is wrong, and worth correcting up front.

What the standards actually say

For domestic extension foundations under NHBC warranty, NHBC Standards Chapter 3.1 calls up standardised prescribed mixes ST1 to ST5, drawn from BS 8500-2. The mix used for strip foundations is ST2, with consistence class S3 (a 50-90mm slump, meaning the concrete is moderately fluid). ST2 corresponds to a roughly 1:6 cement:ballast site mix when measured by volume. ST3, used for higher-load applications, is closer to 1:5. The exact NHBC weight specification for ST2 is 265 kg cement plus 760 kg sand plus 1,135 kg coarse aggregate per cubic metre at cement strength class 42.5.

Translating that into homeowner language: for a domestic extension foundation, 1:6 ballast:cement by volume is the right mix. 1:5 is the slightly stronger version, used where the engineer specifies a higher strength or where vehicle loading is involved. 1:8 is too lean for any structural foundation work.

The ratios you'll actually use

Most domestic ballast jobs fall into one of three mix ratios. Pick by application.

The reason foundation concrete can use a leaner mix than a driveway is structural. Driveways rely on surface hardness and abrasion resistance. Foundations rely on mass and confinement: a 600mm-wide trench full of concrete supports load through volume and the surrounding soil that confines it, not through surface strength. The misleading "1:8 for foundations" advice in some guides probably originates from sub-structural applications (blinding layers, mass fill) where lean mixes are appropriate. Apply that to a load-bearing footing and you've under-strength concrete carrying your wall.

If your structural engineer specifies a particular strength class (C20, C25, C30) or an NHBC standardised mix (ST2, ST3, ST4), follow that specification. For pours over about 1m³, switch to ready-mix or volumetric concrete with a delivery ticket showing the grade. Site-mixing by volume is hard to evidence to a building control officer, and BCOs reject hand-mixed structural concrete on most extension foundations. Use site-mixed ballast concrete for non-structural and ancillary work. Use ready-mix for structural work.

How to work with it

Weight and handling

A standard bulk bag of all-in ballast contains around 850kg, which equates to roughly 0.5m³ of loose material. Bulk density is 1,780-1,800 kg/m³ on average, with 5-10% variation depending on moisture content. A wet bulk bag can weigh well over a tonne. The bag itself is a woven polypropylene sack with lifting loops at the corners, designed to be craned off the delivery lorry. Most merchants offer HIAB crane delivery on orders of 10+ bags; for one or two bags, the lorry usually has its own offload crane.

Position the bag where you actually need it. Bulk bags are nearly impossible to relocate once placed. Tearing the bottom open with a shovel and shovelling out 850kg of damp aggregate while moving it 10 metres is a job that ruins a Saturday.

A 25kg retail bag is just liftable by one person. For anything above about half a tonne, switch to bulk bags. For anything above 5 tonnes, switch to a loose tipper delivery. It's far cheaper per tonne, but you need somewhere to dump it (a driveway, a yard, on top of polythene sheeting if dumping on grass) and you'll be shovelling it from the pile.

Mixing

For any quantity above a couple of buckets, use a petrol or electric concrete mixer rather than hand-mixing in a barrow. The standard domestic mixer holds about half a bag of cement plus matching ballast per drum-load (roughly 0.04m³ of mixed concrete). At a 1:6 ratio, that's around 25kg cement plus 150kg ballast plus water per load.

The single most important rule when mixing ballast concrete is measure by bucket, not by shovel. Cement slides off a shovel; ballast heaps. Eight shovels of one and one shovel of the other will give you wildly different ratios depending on shovel angle, ballast moisture, and operator fatigue. A 10-litre bucket holds about 18kg of cement or about 18kg of damp ballast, so the same bucket measured level gives you a consistent ratio.

The water-cement ratio is more important than the cement-ballast ratio. Add too much water and the concrete is dusty and weak. The strongest domestic mixes are the ones that look "too dry" to mix properly. They take more effort to compact, but cure to twice the strength of a sloppy mix. The community consensus across BuildHub, DIYnot, and Screwfix forums is unanimous on this: water sparingly, and accept a stiffer mix. NHBC inspectors flag over-watered concrete as one of the most common foundation defects.

Storage and weather

Cover bulk bags with a tarpaulin if they'll be on site for more than a few days. Open ballast picks up leaves, blown topsoil, animal droppings, and other organic contamination. Frozen ballast cannot be used until thawed; ice crystals in the mix create voids that survive curing.

NHBC guidance is clear: don't pour on frozen ground, don't let fresh concrete drop below 5°C, and protect curing concrete with insulated blankets in cold weather. Concrete is walkable after 24-48 hours but reaches its full design strength at 28 days. Allow at least 7 days of curing before any load is placed on a fresh slab, and longer in cold weather.

How much do you need

A cubic metre of finished concrete from all-in ballast at a 1:6 mix needs approximately:

• 1.4 tonnes of ballast (about 1.7 bulk bags at 850kg each)
• 9-10 bags of 25kg cement (or roughly 230kg)
• 140-150 litres of water (depending on ballast moisture)

At 1:5 the cement quantity rises to about 11-12 bags per cubic metre and ballast drops to around 1.35 tonnes. The wet-to-dry volume multiplier is approximately 1.54. You need 1.54m³ of dry materials to produce 1m³ of compacted wet concrete, because the cement paste fills voids between the aggregate.

Add 5-10% wastage on top of any calculated quantity. Trench shapes are uneven, some material spills during mixing, and running short mid-pour creates a cold joint in the concrete (a weak boundary between old and fresh) that can cause cracking later.

Worked example: shed base, 4m x 3m at 100mm depth

Volume of finished concrete: 4 × 3 × 0.1 = 1.2m³.

At a 1:6 mix: 1.7 tonnes ballast (2 bulk bags) plus 12 bags of 25kg cement, with about 5% wastage allowance.

For materials pricing, the bulk bag and cement bag entries are the two key inputs:

£55 – £85 £6.50–8.50

Two bulk bags plus 12 bags of cement (per the rates above) cover the ballast and binder for this 1.2m³ shed base. A volumetric ready-mix wagon would deliver the same 1.2m³ at roughly the same all-in materials cost plus a delivery charge, typically a wash, and saves you a day of mixing. For volumes above about 1m³, ready-mix usually wins on time and effort even if the per-cubic-metre cost is similar.

Worked example: 30m² oversite slab at 100mm

Volume: 30 × 0.1 = 3m³.

Required at 1:6: about 4.2 tonnes of ballast (5 bulk bags or a part-tipper load) plus 30 bags of 25kg cement.

For 3m³ you should not be hand-mixing. The labour involved (around 30 mixer-loads per cubic metre, roughly 90 loads total) is a full day for two people, the quality consistency is poor, and the concrete starts setting within 30 minutes of water being added. Order ready-mix or volumetric. The all-in cost is similar; the time and quality are not.

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Cost and where to buy

All-in ballast is sold in three formats: 25kg retail bags (B&Q, Wickes, Screwfix, Toolstation), 850kg bulk bags (all major builders' merchants and DIY sheds), and loose tipped deliveries (specialist aggregate suppliers, builders' merchants on bulk orders).

£4 – £5 £55 – £85 £40 – £70

The format break-points are simple. Under 0.2m³ of concrete, retail bags are tolerable. Between roughly 0.2m³ and 5m³, bulk bags are the right choice. Travis Perkins, Jewson, Buildbase, and MKM all stock them, and most will deliver next-day or 2-day with HIAB offload. Above 5 tonnes (around 6m³ of concrete), loose tipped is dramatically cheaper per tonne, provided you have somewhere to dump it and a way to keep it tidy.

The main retail/trade price gap shows up at the 25kg bag level. The B&Q Tarmac "Large Bag" (weight not specified on the listing) sits around the top of the retail per-bag range and works out to roughly 16-18p/kg if you assume a 25kg fill. A bulk bag is closer to 8-10p/kg, and a loose tipper load lands at 4-7p/kg. Buying retail bags for any job over a few hundred kilos is throwing money away.

The Aggregates Levy effect on price

The UK Aggregates Levy applies to commercially exploited sand, gravel, and rock in England, Wales, and Northern Ireland (Scotland operates separately). The current levy rate is set out in £2 and steps up by a few pence each spring. Merchant prices include the levy, so any ballast price drift you've seen since 2024 is mostly the levy rather than underlying commodity changes.

Trade accounts at Travis Perkins or Jewson give access to lower branch prices, but discounts are negotiated per branch based on volume and relationship rather than published as a fixed percentage. For a one-off domestic job the application overhead rarely justifies the saving; for ongoing project use, set up a trade account at the merchant your builder uses.

Major UK suppliers

The big four national merchants for ballast are Travis Perkins, Jewson, Buildbase, and MKM. Wickes and B&Q stock retail and bulk bags but are typically slightly more expensive than the trade merchants for the same product. For loose tipper deliveries, regional aggregate suppliers (Tiny Tipper in the South East, Mainland Aggregates nationally, Country Supplies in the Midlands) often beat the big merchants on per-tonne pricing for orders above 5 tonnes.

Ready-mix as the alternative

For any pour over about 1m³ where access allows a concrete truck within 3-4m of where you're pouring, ready-mix is the right answer. Site-mixing 1m³ of concrete with all-in ballast and a small mixer takes a fit person around 4-5 hours of continuous mixing. Ready-mix arrives in 15 minutes and discharges in another 15. The per-cubic-metre cost works out broadly similar once you tally the bulk-bag rate plus 25 bags of cement against the C20 ready-mix rate, but ready-mix gives you consistent quality and a delivery ticket that proves the grade to building control. See the £55 – £85, £6.50–8.50 and £90–115/m³ figures above to compare.

For pours of 0.5m³ to 4m³, volumetric concrete is the sweet spot. A volumetric truck mixes concrete on-site from raw materials, charges only for what you use, and avoids the short-load surcharge that ready-mix suppliers apply on orders below 4-5m³. Ask for a volumetric quote alongside a ready-mix one for any pour in this range.

For load-bearing extension foundations, the answer is almost always ready-mix or volumetric, not site-mixed ballast concrete. See ready-mix concrete C25 for the full picture on foundation concrete specification, building control compliance, and ordering.

What to check on delivery

When the bulk bags or tipper load arrives, do four checks before signing the delivery ticket.

Weight matches the order. A bulk bag should weigh roughly 850kg. Tipper loads should match the ticket weight to within 5%. If the driver can't show you a weighbridge ticket, query it.

Visible composition. A clean cut bag should show pale grey or yellow-brown sand mixed with rounded gravel up to 20mm. If you only see gravel, you've been sent coarse aggregate by mistake. If you only see sand, you've been sent sharp sand. Both are common merchant errors.

No contamination. Look for clay lumps, organic matter (twigs, roots, leaves), or dark patches that suggest topsoil contamination. Reject bags with visible contamination. Once it's in your concrete, it stays there.

Moisture sanity check. Damp ballast is normal and expected. Saturated ballast (water pooling at the bottom of the bag, the bag visibly heavier than the others) reduces effective volume and skews your mix-water calculation. Note moisture condition on the delivery sheet so you can adjust water added during mixing.

If anything fails these checks, refuse the delivery before the truck leaves. Once the driver has unloaded and gone, returning bags is a logistical and commercial argument you'll usually lose.

Common mistakes

Ordering ballast when you needed sharp sand, or vice versa. Builders ask for one or the other; homeowners often write down the wrong word. Confirm in writing before placing the order. If the job is mortar, screed, or a paving bed, you need sharp sand. If the job is concrete, you need ballast (or sharp sand and coarse aggregate batched separately).

Using 1:8 for a structural foundation. See the KeyFact above - NHBC ST2 (roughly 1:6) is the right mix for domestic strip foundations, not 1:8.

Hand-mixing structural concrete for a building-control inspection. BCOs reject site-mixed concrete for structural foundations on most extension projects. The BS 8500 compliance evidence isn't there. For foundations, oversite slabs over 25m², or anything else your BCO will inspect, order ready-mix or volumetric with a delivery ticket.

Adding too much water. The single most common cause of weak, dusty concrete. Aim for the stiffest workable mix. The community wisdom across every UK forum is consistent: water sparingly, compact thoroughly. A mix that "looks too dry" cures stronger than one that looks easy.

Buying 25kg bags for jobs over a few hundred kilos. The cost-per-kg of retail bags is roughly double that of bulk bags and four times that of loose tipper loads. Three bulk bags cost less than 30 retail bags and contain three times the material.

Storing ballast on bare soil. Silt and clay contamination from below seeps into the bottom of the bag. Always store on a hard surface or on top of polythene sheeting.

Where you'll need this

• Foundations and footings for ancillary concreting around the main foundation pour. Structural footings should be ready-mix.
• Damp proof course for oversite concrete and patching work below DPC level.
• Walls and blockwork for filling cores in concrete blockwork and bedding any post bases set into the wall line.

These materials appear across all stages of any extension or renovation project where small-volume concrete is mixed on site. For load-bearing structural work, ready-mix is the right choice. For ancillary concreting, all-in ballast and a mixer is faster, cheaper, and entirely standard practice.