Grab a handful of builders sand and a handful of sharp sand and you'll feel the difference straight away. Builders sand runs soft and fine through your fingers, almost like flour. Sharp sand feels gritty and angular, more like something you'd find on a riverbed. That texture isn't just a curiosity. It's the reason one will hold your bricklaying mortar together and the other will hold your patio up for the next twenty years, and why swapping them over is one of the most common mistakes we see at the yard.
What is builders sand?
Builders sand, also called soft sand or bricklaying sand, is a fine, rounded-grain sand. It's screened to take out stones and larger particles, which is what gives it that soft, almost powdery feel.
Because the grains are small and rounded, builders sand mixes into a smooth, workable paste when you add cement and water. That's exactly what you want for:
- Mortar for laying bricks and blocks
- Rendering external walls
- Pointing brickwork and patio joints where you want a neat, smooth finish
- Play sand for children's sandpits (though buy a washed, graded product for this, not standard builders sand)
What it's not good for is anything that needs to bear weight or resist compaction over time. Soft sand holds water, and a mortar mix made purely with it stays slightly springy even once it's cured. Fine for a joint between two bricks. Not fine under a two-tonne patio.
What is sharp sand used for?
Sharp sand, sometimes called grit sand or concreting sand, is coarser and made up of angular, rather than rounded, grains. Those sharp edges lock together under pressure instead of sliding past each other, which is why it's the sand you want anywhere strength and drainage matter more than a smooth finish.
Typical uses:
- Concrete mixes, for foundations, fence post footings, and slabs
- Bedding mortar under paving slabs and flags
- Backfill around land drains and French drains, where good drainage matters more than binding
- Screeds and other jobs where the mix needs to compact hard and stay put
If you've ever laid a patio and had a slab rock within a year, there's a fair chance the bedding mortar was mixed with the wrong sand. We've re-laid enough Wiltshire patios to know it's one of the most common jobs that comes back to us.
Builders Sand vs Sharp Sand: Which Do You Need for the Job?
Here's the quick answer for the jobs we get asked about most.
| Job | Sand to use | Why |
| Laying bricks or blocks | Builders sand | Fine grain gives a smooth, workable mortar |
| Rendering a wall | Builders sand | Needs to trowel smooth and level |
| Pointing patio joints | Builders sand (with cement or a jointing compound) | Fine finish that doesn't look gritty in the joint |
| Bedding mortar under paving slabs | Sharp sand | Compacts hard, drains well, won't stay soft under weight |
| Concrete for posts or foundations | Sharp sand | Angular grains give the mix real strength |
| Block paving joints | Kiln dried sand (a separate product) | Fine and completely dry so it brushes into narrow joints |
| Land drainage backfill | Sharp or coarse sand | Drains freely, doesn't clog |
Sand for Laying Patio Slabs: Get This Bit Right
This is the one that catches people out most, so it's worth spelling out properly. When you're bedding paving slabs, you mix sharp sand with cement, usually around 6 parts sand to 1 part cement, to a semi-dry consistency. Semi-dry means if you squeeze a handful, it holds its shape but no water runs out. Too wet and the bed will slump under the slab. Too dry and it won't compact evenly, which is how you end up with a slab that rocks the first time someone stands on the corner of it.
Lay the bed at roughly 30 to 50mm thick, and go firmer rather than thinner if the ground underneath is at all soft. A lot of the older properties around Swindon and the surrounding villages sit on heavy clay, and clay moves with the seasons far more than sandy or chalky ground does. A shallow bed on clay is asking for trouble come the first proper wet winter, when the ground swells and slabs that were dead level in summer start tipping.
Common Mistakes We See Come Back to the Yard
- Using builders sand for a patio bed. It looks the same once it's bagged up, but it won't compact properly and holds too much moisture. Slabs laid on it tend to work loose within a year or two.
- Using sharp sand for pointing. It'll do the job structurally, but the finish is rough and gritty, not the neat line most people want on a visible patio joint.
- Assuming all "sand" on a delivery note is the same thing. If you're ordering for a trade job with a few different tasks on the go, check what's actually going in each bag or bulk bag before your team starts mixing.
- Guessing quantities. A rough rule of thumb is one bulk bag of sharp sand will bed around 15 to 20 square metres of patio at a standard depth, but that varies with slab thickness and how uneven your base is. If you're not sure, it's worth asking before you order, since running short mid-job on a Saturday afternoon is never fun.
Getting the Right Sand for Your Project
If you're still not sure which one your job needs, that's exactly what the team at Sansums is for. Pop into the yard in Swindon with your measurements, or give us a call, and we'll talk through the job and get you the right sand, in the right quantity, first time. You'll find our full range of building sand and sharp sand online, along with everything else you need for the job, from bedding mortar to the paving slabs themselves.