Key Takeaways
- 20mm slate chippings are the right size for a garden path. They pack into a firm, even surface and take a loaded wheelbarrow without shifting. However, 40mm slate chippings are a border and ground-cover stone, not for paths.
- A slate chippings path is built in layers: dig out 15cm, lay 10cm of compacted MOT Type 1, run a geotextile membrane over that base, then 4 to 5cm of slate. On a path the membrane goes on the sub-base, unless the soil is very soft, where I would use it as a stabiliser.
- Wet slate is slippery: the smooth flat faces that pack so well underfoot lose their grip in rain, so a slate chippings path belongs on level ground and out of permanently damp shade.
- A slate chippings path needs edging and it should be fitted before the stone goes down. No loose surface stays put without a fixed edge.
- Never lay slate chippings for a pathway straight onto soil – they tread in and the surface sinks inside a season. Most failed slate paths I see about have no base underneath at all.
- A slate chippings path needs a rake in spring and autumn, weeds pulled while small, and a top-up roughly every 3 to 5 years.
Slate chippings is the material DIYers get wrong before the work starts. Nine times out of ten it is the same picture: a bulk bag of 40mm chips ordered because it looked the part in the photos, tipped, spread, and a finished path that feels like walking across a stack of roof tiles. The stone was never the problem. The size was.
This guide covers the size to buy, whether slate suits a walkway at all, the base that stops it sinking, and what to do about slate in the wet. For borders and beds, the laying method is in how to lay slate chippings, and a driveway is a different spec again, covered in slate for driveways.
What Size Slate Chippings for a Path?
For a path, 20mm slate chippings are the main size I recommend to clients, and on a main route or anywhere a loaded wheelbarrow goes I would not use anything else: it stays put under that use and still walks comfortably. If your path is lighter-traffic and you prefer the textured look, slate mini mulch, the 4 to 10mm grade, packs flatter than anything in the range and, to be frank, looks great down. One thing to weigh: mini mulch is small enough to lodge in shoes and get carried indoors, which won’t happen with the 20mm. If the path runs to a back door, that calls for the 20mm.
The size to keep off a walkway is 40mm. Those plates tip and slide under a heel, which is fine in a border where nothing heavier than a blackbird lands but miserable under a loaded wheelbarrow. Save them as a ground-cover for borders or rockeries.
| Size | Where it belongs | Underfoot |
|---|---|---|
| Slate mini mulch, 4 to 10mm | Lighter-traffic paths, and mulching and top dressing | Packs flattest of the lot; the most comfortable slate to walk on |
| 20mm slate chippings | Main paths, and anywhere a wheelbarrow goes | Firm and even; takes regular use without shifting |
| 40mm slate chippings | Borders, ground cover, water features | Tips and slides under a heel; hard going on a walkway |
Size also sets your depth. Loose stone gets hard to walk on once it is laid deeper than roughly twice the size of the stone: below that feet skim the top, above it they sink in, which is the trick a motorway gravel trap uses on purpose. So 20mm wants 4 to 5cm and mini mulch nearer 2.5cm. Deeper makes the path worse, not better.
A mistake I see over and over is buying by photograph. 40mm looks dramatic on a screen and is often what people choose, but then every trip to the shed becomes a workout for the ankles. If you have already put the 40mm down and the walkway is slipping, avoid tipping smaller chippings over the top in the hopes of levelling it. Small over large never works: the fine stuff heads down, the large ride up, plus, mixed sizes look a mess. I always move the client’s 40mm to a border, where it earns its keep as mulch, and re-lay the path at 20mm.
Is Slate Good for a Walkway?
TLDR: Level ground, 20mm stone, a rake now and then. On those terms, slate is a superb path.
I have always found that slate chippings make a genuinely good walkway surface, on two conditions: you buy a size meant for feet, and you keep the path on level or gently sloping ground.
The case for slate underfoot is the shape of the stone. Angular stone interlocks in a way rounded stone cannot, and slate takes that further: the chippings are flat plates, so they lie against each other and pack into a firm, even surface. Rounded stone is softer, slate is steadier, and over any distance steadiness wins. It barely weathers and won’t fade, plus, the colour deepens in rain, which is exactly when most garden surfaces look their dreariest.
One thing that supplier guides seem to skip: wet slate is also slippery. The same surfaces that pack so beautifully are the faces your boot meets in the rain. On a level path with a loose, raked surface it’s usually no issue, but that changes on slopes and stretches that sit in shade and never dry. Nor is slate a barefoot stone unless you have tough feet, since fresh chips can have sharp edges. For a shaded, never-dry run, slate is the wrong stone: a crushed angular gravel or even a self-binding gravel gives far more grip.
What Is the Best Base to Put Under a Slate Pathway?
The best base under slate chippings on a path is a minimum 10cm of MOT Type 1, compacted hard, with a heavy duty weed membrane (the grade worth using) laid over the top of it. The sub-base does the weight bearing – the slate is only the wearing surface – and building that base is a job in itself. See how to lay a sub-base. The membrane is a separator, not a magic weed solution, and on light traffic use paths it sits above the sub-base rather than at the bottom of the dig.
The reason follows from which failure you are aiming to prevent. On a driveway a car’s weight drives the sub-base into the soil, so the fabric is buried at formation level. A path carries nothing heavier than you and a wheelbarrow, so the base is going nowhere; the real risk is slate working down into the base and base working up into the slate, and the fabric belongs between those two. The exception is ground that cannot hold anything up, very soft soil or heavy clay, where a second separation layer at the bottom of the dig is worth it. No membrane stops windblown seed landing in the surface; that comes out with the rake. Firm compaction of the MOT Type 1 sub-base is part of the weed defence, too.
How to Lay a Slate Chippings Path
A slate chipping path is the same skeleton as any loose-surface path: dig, base, edge, surface. Here is the slate version. The gravel sibling, with more on membranes and grids, is in how to lay a gravel path.
- Mark it out. A garden hose or a string line for the route. Width matters more than people think: 1.2m lets two people walk side by side, and about 70cm does a single-file side route.
- Dig out 15cm, flat bottom. Decide where the waste is going before you dig. The digging is the biggest job on the whole build; everything after it is quick. If the path runs up to the house, set your depth so the finished slate will sit at least 150mm below the damp-proof course, the waterproof line you can usually spot two brick courses up the wall. Get that wrong and rain splashes above it into brickwork that was never meant to get wet.
- Sub-base in. Minimum 10cm of MOT Type 1, ideally compacted with a hired plate compactor. Treading on it is not compacting it, but a sledgehammer with a board cable tied to it can do a pretty good job if you work at it. Shape a slight crown along the centre so the path sheds rain both ways; a fall of about 1 in 100 is plenty. On very soft ground or heavy clay, lay geotextile before the sub-base too.
- Membrane over the base. One layer of geotextile across the compacted sub-base, run up the trench sides, sheets overlapped 10cm and pinned every 45cm so it cannot creep when the stone goes on. The edging traps the outer edges.
- Edging before slate. Mandatory with any loose surface: it holds the stone, finishes the line and pins the membrane. Timber boards, setts, brick or metal all work for slate path edging, and the methods are in how to edge a garden. But, it goes in before the surface, never after.
- Slate on top. 4 to 5cm of 20mm slate, or about 2.5cm of mini mulch, raked level. Deeper is not better.
- Walk it, rake it, top it up. Expect a little settlement in the first few weeks. A rake-over and a small top-up sorts it.
Slate Paths on Slopes and Gradients
A slate path works on a gentle slope and no more. Past roughly 8%, about 1 in 12, loose slate migrates downhill however well it was laid. Within that limit, gravel grids are the fix: interlocking bottomless cells, roughly 50 by 50mm, laid on the sub-base before the slate goes in. Beyond it, shallow timber-contained steps work like a run of little dams. And remember the wet: a slope is exactly where slippery slate can cost, which is why I keep it for the flat.
Plum, Grey, Blue or Green: Which Colour for a Slate Path?
Colour is taste, with two practical notes. Every slate darkens when wet, so look at the images when it is wet as well as dry. And grey is the lightest, so it does the most to lift a shaded run. Plum slate gives the richest contrast against green planting and makes the boldest path. A grey slate path is the quieter, modern choice. Blue slate sits between the two, and green slate reads soft and natural, sage to olive.
Maintaining a Slate Path
A slate path asks for a rake in spring and autumn, weeds pulled while small, and a top-up every 3 to 5 years. The top-up is not a fault appearing: slate is a soft stone, and where feet concentrate, at a gate or under a washing line, it grinds smaller. A fresh bag every few years is the price of the colour, and for a surface you walk daily that is still about as low as upkeep gets.
The autumn rake is about leaves: litter left to rot on stone becomes the soil weeds seed into, and a leaf blower on a low setting is the best money you will spend on a slate path. Pull weeds as seedlings, not just for tidiness: let one root through into the membrane and yanking it out tears the fabric, which is how membranes fail early. If the chippings dust over or turn hazy, a hose usually clears it; stubborn cases are covered in cleaning garden stones. Snow, if we get any worth the name: skim the bulk off and deliberately leave about 1cm behind, so the shovel takes snow and not slate.
Next Steps
We stock 20mm slate chippings in green, blue, plum and grey, by the bulk bag, with nationwide delivery. Work out the tonnage with the gravel calculator, then have a browse of the slate chippings range. Happy renovating your outdoor space!
If you would rather talk your slate path through with a person, ring Outdoor Aggregates on 0330 043 7585. The office is open 7am to 7pm, seven days a week.
Have you ever used slate chippings on a path? Which grade did you go for, and how has it worn in? Tell us in the comments below.
FAQs
Do you need to put membrane under slate chippings?
Slate chippings do need a membrane under them, and it goes over the compacted sub-base rather than at the bottom of the dig. Its job is to stop the slate and the base mixing into each other, so it belongs between them. I only add a second sheet at the bottom when the ground is very soft or heavy clay.
Can you lay slate chippings on a slope?
Slate chippings only hold on gentle slopes, up to roughly 1 in 12. Loose slate migrates downhill, and wet slate grips worst exactly where you need grip most. Past that gradient I build shallow contained steps or change the surface.
Can you lay slate chippings straight onto soil?
Slate chippings laid straight onto soil tread in and sink within a season, so it is not a build I would use for a path. Bare soil gives the stone nothing to lock against. Straight onto soil is a border treatment, not a walking surface.
How deep should slate chippings be on a path?
Slate chippings on a path want to be about twice as deep as the stone is big: 4 to 5cm for 20mm chippings, and around 2.5cm for slate mini mulch. Any deeper and the surface stops packing down and starts swallowing feet.
Can you put smaller slate chippings on top of 40mm to fix a path?
Topping 40mm slate with a smaller grade will not fix a path, because small over large never interlocks. The fine chippings work down, the plates ride up, and you are back where you started with a messier mix. I would move the 40mm to the borders as mulch and relay the path at 20mm.
Do cats use slate chippings as a litter tray?
Cats will use slate chippings as a litter tray, no different to any other type of loose stone, if the grade is fine enough. The finer the chipping the more it appeals, which is one more argument for 20mm over a mulch grade. Interest usually fades once the novelty does.