Slate’s a bit of an odd one on this list. I see it far more often as a decorative border, or a small patio area, than a full driveway. But when I do get called to a slate job, it plays by its own rules compared to everything else I clean. So it’s worth its own post.
What Is Slate
Where You’ll Usually See It
Why Slate Behaves Differently
The Flaking Problem
How I Clean It
Should You Seal It
FAQs
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What Is Slate
Slate’s a fine-grained metamorphic rock that naturally splits into thin, flat layers. That’s why you’ll recognise it most from roof tiles, it’s the same stone, just used differently underfoot. For paving, it usually comes in dark grey, charcoal or blue-black tones, sometimes with a slight sheen when wet.
Where You’ll Usually See It
I mostly see slate on smaller patio areas, garden borders, or as an accent alongside another main paving stone, rather than covering a whole driveway. It’s a striking, dark, modern look. But it’s a specific style choice, rather than the default like Indian sandstone.
Why Slate Behaves Differently
Slate’s naturally layered structure means it behaves quite differently under pressure and moisture, compared to sandstone or limestone. It’s fairly low-porosity for a natural stone, so it doesn’t soak up water and stain the way sandstone does. But because it’s made of thin layers, it has its own weak point. And that’s flaking.
The Flaking Problem
This is the thing I always mention to slate customers upfront. Because slate is naturally layered, if it’s aggressively pressure washed at close range or with too much force, thin layers of the stone can actually lift and flake away. It’s not common with a careful clean. But it’s a real risk if someone goes at it with a domestic pressure washer held too close for too long. Once a layer’s flaked, that’s permanent, it’s not coming back.
How I Clean It
I keep the nozzle further back on slate than I would on granite, and I never let the surface cleaner sit static in one spot. Sodium hypochlorite handles any algae or moss without an issue, that’s not a pressure concern. It’s purely about mechanical force against the stone’s layered structure. So I go with slower, wider passes, rather than blasting away at close range. It takes a bit more patience, but it’s the right way to do it without risking the surface.
Should You Seal It
I’d lean towards yes, mainly because a sealer helps protect the surface layers and can reduce the risk of moisture getting between them. That moisture is part of what contributes to flaking over the years, especially through freeze-thaw cycles in winter. It’s not essential the way it is on Indian sandstone. But it’s a sensible extra step, given slate’s particular weak point.
FAQs
Yes, if it’s done aggressively at close range. Slate’s naturally layered structure means thin layers can flake off under too much force. Done carefully, it’s perfectly safe.
Usually a combination of moisture getting between the natural layers and freeze-thaw cycles over winter, sometimes made worse by overly aggressive cleaning in the past.
It’s less common for full driveways and more often used for patios or accents. But it can work well if cleaned carefully and not overloaded with heavy vehicle traffic in smaller sections.
It’s a sensible extra step. Sealing helps protect the layered surface and can reduce moisture getting between layers, which contributes to flaking.
Roughly every 12 to 18 months for most properties, since it’s fairly low-porosity and doesn’t stain as fast as something like sandstone.
You can, but keep the nozzle further back than you might think, and never let it sit in one spot. That’s exactly how flaking happens.
General surface dirt and light algae film usually causes dullness rather than damage. A proper clean typically restores the natural sheen.
Yes, it can be, particularly with any algae present. Worth keeping on top of cleaning near steps or doorways for that reason.
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If you’ve got slate that needs a careful clean, send us a few photos on WhatsApp. We’ll tell you honestly what it needs, and treat it the way it should be treated, not blast it like a driveway. 10% off for quoting this way.