Slate patio cleaning is a bit of an odd one for me. I see slate far more often as a decorative border or a small patio than as a full driveway. When I do get called to it, it plays by its own rules. The biggest one is simple. Treat it like any other stone and you can wreck it. So slate gets its own post.
In this post
Can pressure washing damage slate?
Yes, if it’s done aggressively. This is the first thing I tell every slate customer. Slate is naturally layered. Hit it at close range or with too much force and thin layers can lift and flake away.
It’s not common with a careful clean. It’s a real risk with a domestic pressure washer held too close for too long, though. Once a layer has flaked, that’s permanent. It’s not coming back.
Weather plays a part too. Moisture getting between the layers and then freezing over winter can push them apart over the years. Heavy handed cleaning in the past just speeds that up.
How do you clean slate safely?
Slowly, with the nozzle further back. I keep a bigger gap on slate than I would on granite, and I never let the surface cleaner sit still in one spot. Sodium hypochlorite deals with any algae or moss without an issue. The chemical side isn’t the worry. It’s purely about force against those layers.
So I go with slower, wider passes rather than blasting away at close range. It takes a bit more patience. It’s the right way to do it without risking the surface. Clean slate usually gets its natural sheen back once the dirt and algae film are gone.
DIY on slate? Use the widest fan tip your pressure washer has. Keep it moving at all times and stay well back from the surface. If you see little flakes in the water, stop straight away.
What is slate paving?
Slate is a fine grained metamorphic rock that splits naturally into thin, flat layers. You’ll know it best from roof tiles. It’s the same stone, just used underfoot. For paving it usually comes in dark grey, charcoal or blue black, sometimes with a slight sheen when wet.
It’s fairly low porosity for natural stone. It doesn’t soak up water and stain the way Indian sandstone does. Its weak point is those layers, which is why everything above matters so much.
Is slate used for driveways?
Not often. I mostly see slate on smaller patios, garden borders, or as an accent next to another main stone. It’s a striking, dark, modern look. It’s a deliberate style choice rather than the default on most new builds.
It can work on a drive if it’s cleaned carefully and not overloaded by heavy vehicles. It’s more at home on a patio, though. I’ve done slate patios from Aintree to Bebington, and you’ll find some of them on my Facebook page.
Should you seal a slate patio?
I’d lean towards yes. A sealer helps protect the surface layers and can cut down on moisture getting between them. That moisture is part of what causes flaking over the years, especially with winter frosts. It’s not essential the way it is on sandstone. Given slate’s particular weak point, it’s a sensible extra step.
If you’ve got something pale and smooth instead, have a look at my guide to limestone. It has its own set of rules, and they’re nothing like slate’s.
FAQs
Driveway and patio cleaning starts from £100. Slate patios are often on the smaller side, which helps. The careful, slower passes I use on slate take a bit longer than a granite or porcelain clean of the same size. Whether you add sealing also changes the price. To get an exact figure, send me a few photos on WhatsApp to 07469 539 068. I normally reply within about five minutes. You get 10% off for quoting that way because it saves me the fuel of driving out to look. You can also ring 0151 272 3404 if you want to talk it through first.
A wide shot showing the whole patio or border, and a couple of close ups. If any slabs are already flaking or have bits missing, get those in clearly. It helps me see whether the stone has been damaged before and how careful I need to be. Show me any steps or edges too, because they’re where flaking often starts. A short video walking across it is just as good. I’ll come back with a price, usually within about five minutes. I’ll also tell you straight if I think any slabs are too far gone to clean without making them worse.
A little longer than you might expect for the size. Slate patios are often small, but I don’t rush them. Slower, wider passes with the nozzle held further back take more time than going at it hard. That’s the trade off for not lifting the layers. Most of the time is spent on the passes rather than setting up. I’ll give you a rough idea of how long I’ll be when I quote from your photos. If you want it sealed as well, the slate needs to be properly dry first. In damp weather that can mean coming back for a second visit.
Usually, yes. When slate looks dull it’s normally surface dirt and a light film of algae rather than damage. Once that’s lifted, the natural dark colour and sheen tend to come straight back. It looks best when it’s wet, so give it a while to dry before you judge it. What a clean can’t fix is slabs that have already flaked. Those patches will look lighter and rougher than the rest, because a layer has come away and it’s gone for good. I’ll point out any of those from your photos so you know what to expect before I start.
Usually it’s moisture getting between the natural layers and then freezing over winter. Each frost pushes the layers apart a tiny bit more. Over a few years the top layer starts to lift and break away. Aggressive cleaning in the past can make it much worse, especially a domestic pressure washer held close to the surface. Poor quality slate is also more prone to it than good stone. A careful clean won’t cause flaking, but it won’t reverse it either. Sealing afterwards can help by keeping water out from between the layers. If yours is flaking badly, send me a photo first.
You can, but be careful. Keep the nozzle further back than you think you need to and never let it sit in one spot. That’s exactly how flaking happens. Use the widest fan setting you’ve got and avoid the rotating turbo heads that come with some machines. They’re far too aggressive for slate. Keep an eye on the water running off. If you see flakes or dark grit coming away, stop. A hose down alone won’t kill the algae either, so it’ll come back quickly. If you’d rather not risk it, send me some photos and I’ll give you a price.
Roughly every 12 to 18 months for most properties. Slate is fairly low porosity, so it doesn’t stain as fast as something like sandstone. Shaded patios and borders under trees will need it sooner because algae gets going faster in the damp. Open, sunny ones can last longer. Sweeping off leaves and keeping water from pooling on it both help. Less standing water also means less moisture getting into the layers through winter. I’d also suggest cleaning it before it gets really bad. Lighter, regular cleans are kinder to slate than one heavy clean every few years. My post on how often to jet wash covers the general signs.
Yes, it can be, particularly once algae has built up on it. Smooth slate already has less grip than a riven stone, and a green film makes it far worse. Steps and doorways are where people get caught out. Keeping on top of the cleaning is the best fix. Once the algae is gone, slate is much safer underfoot. A biocide after the clean slows the green coming back for months. If anyone in the house is unsteady, it’s worth sorting before the wet months arrive. My post on why patios go slippery in winter explains why it gets so much worse from autumn onwards.
Usually without any trouble. I carry 50 metre hoses, so I can reach most back gardens from the van down a side path or through a gate. I don’t need to come through the house. I’ll need an outside tap or another water source, and the gate left unlocked if you won’t be home. Slate borders often sit right against flower beds, so tell me about anything delicate nearby. I’ll keep the spray away from it. Mention your access when you send your photos and I’ll plan the job before I turn up, so there’s no messing about on the day.
Yes, as long as it isn’t freezing. I clean all year round, and cold on its own isn’t a problem. A hard frost is different. Water left on slate can freeze in the surface and between the layers, which is the very thing that causes flaking. So on frosty days I won’t touch it. Rain is fine for the clean, but sealing needs the slate properly dry. In winter I’ll often clean on one visit and come back to seal on a dry spell. If the forecast looks wrong for your job, I’ll let you know and move it rather than take a chance with your stone.
Got slate that needs a careful clean?
Send me a few photos on WhatsApp and I’ll tell you honestly what it needs. I’ll treat it the way slate should be treated, not blast it like a driveway. You get 10% off for quoting this way.
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