You may have heard that you need an ‘aggregate’ of different types for different layers when laying a foundation for things such as paths, sheds, and patios – but what exactly is it?
The word ‘aggregate’ literally means “something formed by combining several separate elements” – so construction aggregate isn’t one thing, it’s instead a combination of different materials and sizes to create a certain desired effect.
In order to fully understand aggregate, we need to understand why and how foundations are laid.
Why you need foundations
While it may seem clear to some, it’s often not intuitive that you can’t just put some paving slabs on top of the grass and use them as a path. The fact of the matter is that you can do that, it just won’t last very long, and you’ll end up with a wobbly path after the first few rain showers.
Where there’s soil, there’s ground movement. This is because the soil is composed of varying materials (such as organic matter, clays, sands, and so on). Most of this material absorbs and holds water at different rates and to different extents.
So as soon as there’s rain, some parts of the soil will expand much more than others and you get what’s called “ground heave”. Similarly, if you just put a slab on the soil and keep walking on it, it’ll eventually sink into the soil.
In essence, then, the whole point of a foundation for anything is to provide a base for it to stay there. If you’re going to go through the effort of laying a path or a patio, you may as well do it right the first time so that it’ll still be there decades later.
Foundations are laid in layers
In order to stop movement, you need to apply as many non-porous materials as possible in layers. Properly layering the materials helps with adequate drainage and enables the different layers to compact together into a rock solid sub-surface.
A key question then is: how do you stop the stones themselves from sinking into the soil?
Historically, you’d have to dig deeper and start with large stones while layering your way up to finer aggregates of materials. But these days – and especially for things like patios and garden paths – you’re usually able to start with a geotextile and some coarse aggregate before layering up to finer materials.
So what exactly is aggregate?
Aggregate is a combination of larger stones of various sizes with smaller materials of various sizes. The combination of stones of different sizes essentially means that they can be compacted together better.
Think about putting some stones in a bucket: if you only have large stones then there’s a lot of room between them – which then means that if parts break then everything shifts. But if you fill in those gaps with smaller stones (down to pea-sized stones), then you create a really stable surface.
The actual types of stone used in aggregate can vary, and can even be recycled things like old concrete that’s been crushed down to size.
MOT Type 1 is a type of aggregate often used for road sub-bases, but is suitable for a variety of applications Ballast, on the other hand, is a combination of sand, stone, and gravel that is perfect for creating garden walls, paving, stepping stones, and bases. This is largely due to the strength it brings when added to concrete.
Another of our aggregates is shingle. Depending on the size you purchase, shingle can be the perfect material for decorative purposes or for use as a fill aggregate.
We also carry coarse sands and crushed granite. The coarse, or ‘sharp’, sands are optimal for applications where less flexibility but more strength is needed. The granite, however, is great for drainage and can provide a rustic look to any patio or driveway.
You can purchase our aggregates in both bulk and small bags.
In almost all cases, the coarse aggregate layer is the first to be laid on top of the geotextile, then followed either by a finer aggregate or – for applications that don’t require a great deal of load-bearing – straight to sharp sand for final leveling.
Order aggregate online
Ordering aggregate online doesn’t need to be complicated. With Alsford, in fact, it’s never been easier. Besides, aggregates tend to be predictable. They’re needed in specific sizes for different jobs, so you don’t necessarily need to go and inspect the aggregate in question.
There are plenty of benefits to ordering online. For a start, aggregate can get pretty heavy, especially if you are ordering bulk bags. Save yourself the effort and have one of Alsford’s team deliver your order right to your door with their specialist crane offload service.
Another benefit to ordering aggregate online is the time you save. If you are pushed for time or looking to purchase materials ahead of time, you can order them the be collected in branch.
You can browse our full range of aggregates here and save yourself the trip to the timber and builders merchants.