Sharp Sand vs Building Sand vs Kiln-Dried Sand
Last updated: September 2026
Walk into any builders' merchant and you'll find several types of sand at similar prices. They're not interchangeable. Using the wrong one is a common cause of weak mortar, crumbling joints and patios that move.
Quick guide
| Job | Sand to use |
|---|---|
| Bricklaying and blocklaying mortar | Building (soft) sand |
| Patio bedding (mortar bed) | Sharp sand |
| Concrete (with cement and gravel) | Sharp sand, or ready-mixed ballast |
| Floor screed | Sharp sand (screeding sand) |
| Block paving laying course | Sharp sand |
| Block paving joints | Kiln-dried sand |
| Artificial grass infill | Kiln-dried silica sand |
| External render | Plastering or rendering sand |
Building sand (soft sand)
Building sand has fine, smooth, rounded grains. It makes a smooth, workable mortar that “hangs” on the trowel, which is why bricklayers use it. It's too fine and weak for concrete, screed or bedding patios, where it can shrink and crack. It's often yellow or orange.
Sharp sand (grit sand)
Sharp sand has coarser, angular grains that lock together, making it much stronger once compacted or mixed with cement. It's used for patio bedding, block paving laying courses, screed and concrete. It's too coarse for smooth brickwork mortar. Concreting sand and screeding sand are types of sharp sand.
Kiln-dried sand
Kiln-dried sand is very fine, dried in a kiln so it flows freely. Brushed into block paving joints, it trickles all the way down and locks the blocks together. Damp sand clogs at the top of the joint. It's also used to weigh down and support artificial grass. Keep bags dry until you use them.
Plastering and rendering sand
This is a washed, graded sand that's finer than sharp sand but cleaner and more consistent than building sand. It's used in sand and cement render.
How much sand do you need?
Work out the volume (area × depth in metres) and multiply by about 1.6 tonnes per m³. For example, a 40mm patio bed under 15m² of slabs needs 0.6m³, or about 1 tonne of sharp sand. The Sand Calculator gives the answer in tonnes, bulk bags and 25kg bags. For mortar, use the Mortar Calculator, which works out sand and cement together.
Buying tips
- An 850kg bulk bag is much cheaper per tonne than 25kg bags once you need more than about 300–400kg.
- Store sand covered to keep out rain, leaves and cats.
- Buy all the sand for one job at the same time – colour can vary between batches, which shows in mortar joints.
Frequently asked questions
Can I use building sand for a patio?
Not for the bedding layer – it's too soft and can shrink. Use sharp sand.
Can I use sharp sand for bricklaying?
It's too coarse for smooth mortar. Some builders mix in a little sharp sand for strength, but standard bricklaying mortar uses building sand.
What sand goes between paving slabs?
Slab joints are usually filled with mortar or a jointing compound, not loose sand. Kiln-dried sand is for block paving joints.
Is play sand the same as kiln-dried sand?
No. Play sand is washed but not always dry or fine enough for paving joints.