Key Takeaways
- Size before colour. I use 20mm slate chippings for anywhere feet go and keep 40mm for borders, ground cover and around ponds. Laying 40mm on a walkway is the most common slate regret I hear requiring a fix.
- Never tip smaller chippings over larger ones to try fixing a sizing mistake. The two different sizes will not knit together and the big pieces end up back on the surface like the last cornflakes of the box.
- Lay 20mm slate 4-5cm deep and 40mm slate 5-6cm deep. Anywhere you walk, loose stone laid much deeper than twice its own size moves underfoot, so deeper is not safer.
- A bulk bag of slate chippings covers roughly 10-12 square metres at 5cm deep, and colour varies between quarry loads, so try to order the whole job in one batch.
- Avoid slate chippings for a driveway with moderate or heavier use – choose an angular gravel. Flat slate slides and slowly crushes to dust under turning tyres – angular stone interlocks, resisting movement.
A lot of the slate jobs I take on are not installations. They are rescues. The classic version goes like this: a client orders two bulk bags of 40mm slate for their garden path project without realising that chippings come in different sizes. She lays the lot, and rings me because the path look like a quarry floor and is miserable to walk on. The first question is always the same: can we just tip some 20mm over the top? No. They usually had to move the 40mm into the borders, where it has been doing a lovely job as mulch ever since, and laid the paths again in 20mm.
That is the thing about laying slate chippings. The work itself is one of the easier landscaping jobs going, a weekend with a shovel and a rake. Whether the slate behaves for years or ends up as a cautionary post on reddit is decided before the first barrow load, by: the size, the depth, and what holds the edges.
This guide covers laying chippings in garden borders, as mulch and on paths, with a straight answer on driveways too. It is written around slate, but the sizing and depth rules hold for any stone chipping: granite, limestone, flint and the rest all behave the same way underfoot. For the full path and driveway builds themselves, I have separate step-by-step guides on how to lay a gravel path and installing a gravel driveway, and the groundwork in both applies to slate just the same.
Which Size Slate Chippings Should You Use?
The short version: <20mm if feet touch it, 40mm if they do not, mini mulch for pots and gaps, paddlestones for decoration only.
I use mini mulch or 20mm slate chippings for paths, patios and anywhere that gets walked, and 40mm for borders, ground cover and around ponds. Slate is flat, so the <20mm pieces pack down into a surprisingly even surface underfoot, while 40mm gives bolder texture and better coverage per bag in places no one stands.
Slate mini mulch, the small 2-10mm offcuts from slate processing, is also the one for pot dressing, gaps between slabs and tight planted areas. Slate paddlestones, the big 50-150mm flat pieces, are strictly decorative: pond edges, feature areas, the top of a rockery.
And the mistake I opened with: if you have already laid the wrong size, move it rather than mix it. Two sizes of slate in one bed never mesh together. The small stuff filters down, the big pieces ride up, and within months you are looking at 40mm again. Redistributing oversized slate into the borders as mulch is nearly always the cheapest fix, because there it is genuinely good at its job.
On colour, we are spoiled: blue, grey, plum and green are all in our slate chippings range. Two things I tell every client before they choose. First, slate is really two different stones, dry and wet. Dry blue slate is a soft grey-blue; rained on, it goes near-navy and shines. Look for images in both states to see what you will get. I learned that one at my own expense, ordering early in my career from a photo and finding the delivered load a shade greyer than I had promised the client. Second, slate is inert, so it will not sweeten your soil the way limestone chippings can, so it’s safe for use around rhododendrons, camellias and acid loving plants.
How Deep Should Slate Chippings Be?
Lay 20mm slate chippings 4-5cm deep, 40mm chippings 5-6cm deep, and paddlestones one stone thick, which usually works out at 6-10cm. Paths want the same 4-5cm of <20mm slate, just sitting on a proper sub-base rather than soil.
The rule I work to explains why: anywhere that gets walked on, loose stone stops behaving once it is laid deeper than roughly twice its own size. At the right depth, feet skim across the top. Go much deeper and every step sinks and shifts. Race circuits use exactly this behaviour on purpose, in the gravel traps that stops cars at the end of a straight. Lay your slate 15cm deep in a traffic area because you read it online and you have built one of those in your back garden.
| Size | Best for | Laying depth | Coverage per bulk bag (approx.) |
|---|---|---|---|
| Slate mini mulch (2-10mm) | Paths, pots, gaps between slabs, dressing planted beds | 3-4cm | Goes furthest, roughly 15m² |
| 20mm slate chippings | Paths, patios, anywhere walked | 4-5cm | Roughly 12m² |
| 40mm slate chippings | Borders, ground cover, around ponds | 5-6cm | Roughly 10m² |
| Slate paddlestones (50-150mm) | Feature areas and pond edges, no foot traffic | One stone deep, 6-10cm | Varies with stone size |
To work out quantities, measure the length and width in metres, multiply for the area, and put the numbers through our gravel calculator with your depth. It converts straight into the various bag sizes available. One ordering habit worth copying: where possible, order the whole job from a single batch, with a little spare. No two quarry loads are quite the same, and a top-up bag next spring from a different load will sit a slightly different shade until the weather blends it in.
Can You Lay Slate Chippings Straight on Soil?
Yes. For borders, beds and ground cover, laying slate chippings on soil works well, provided you clear the weeds properly first and decide up front whether a membrane goes underneath. Here is my order of work:
- Mark it out. Garden hose or string for curves, pegs for straight runs. Wait and observe the shape for a day before you start to dig.
- Clear and dig. Every visible weed comes out with its roots – I tend to do this as I excavate to the laying depth, 5-6cm for 40mm slate. Keep the base reasonably level and firm it with your boots or use a hand tamper
- Decide on membrane. Where weed pressure is high, and it’s just a border with perennial shrubs, I might use a thick weed membrane. Pin it every half metre, with joins overlapped by at least 30cm to keep the ground below sealed off. Where you want spring bulbs or self-seeders coming up through the slate, skip it: a decent depth of slate on clean soil suppresses most weeds by itself, and daffodils will push through happily. There is more on choosing fabric in what to put under gravel.
- Spread and rake. Barrow the slate into piles around the area first, then rake once to depth. Far less raking that way.
One thing the fabric adverts will not tell you: membrane only stops weeds from below. Give it three or four autumns of rotted leaves and the weeds germinate in the debris sitting on top of the fabric instead. That is why gardens with “membrane and slate” still green over. The fix lives in the maintenance section, not in buying a thicker fabric.
One warning for a border that runs along the house wall. The finished slate has to sit at least 150mm below the damp-proof course, which is the thicker line of mortar a couple of brick courses up from the ground. That is a Building Regulations requirement rather than my preference, and topping a border up every couple of years is the quiet way people end up bridging it and finding damp on the inside of the wall. If the gap is already tight, dig the border down rather than building the level up.
How Do You Lay a Slate Chippings Path?
A slate chippings path is a different build from a border: dig out about 15cm, compact 10cm of MOT Type 1, run a geotextile membrane over that base, then 4 to 5cm of 20mm slate on top. The slate is only ever the finish, and the sub-base is the path. Edging is not optional, and it goes in before any stone. I have written the whole build up properly, including what to do about wet slate and slopes, in building a slate chippings path. Also, where the slate is going into an entertaining area rather than a route, the same build at patio scale is covered in how to lay a gravel patio. Patios explained covers how loose stone compares with slabs, blocks and concrete.
Are Slate Chippings Any Good for a Driveway?
In my opinion, no, not for a daily driveway, and that is the answer most sellers’ pages will not give you. Slate is flat, so the pieces slide over each other instead of locking together the way angular gravel does. Under a turning tyre it migrates towards the road, and over a couple of years it slowly crushes down to dust and flakes. I have re-laid enough tired slate chipping drives to have a settled view: for daily traffic, a 10-20mm angular driveway gravel is the better stone.
If your heart is set on the slate look, it can be made to work on a flat drive with light use: 40mm slate, gravel grids pinned over an immaculately compacted sub-base, solid edging, and an acceptance that you will be topping up. I cover the trade-offs properly in slate chippings for driveways. Oh, and be warned: a warm, loose slate chippings drive is a magnet for every cat in need of a loo on the street.
How Do You Keep Slate Chippings Looking Good?
Slate needs less looking after than almost any surface I lay, but not none. The one job that matters is getting leaves off every autumn, with a blower, a spring-tine rake used gently, or by hand, before they rot down. That leaf litter is the seed bed for the on-top weeds I mentioned earlier, so this is weed control disguised as tidying.
Beyond that, an occasional hose down brings the colour back up. A pressure washer on a low setting is fine for grimy patches, but keep acid patio cleaners well away, as acid is one of the few things that dulls slate permanently. My cleaning garden stones guide has the full routine. Expect to top up a 5cm bed after three or four years as it thins in patches, which is exactly why I keep a spare bag back from the original batch where the budget allows. Fresh slate arrives dusty from the bag, by the way. Either hose it off once laid or simply wait for the first proper rain, and the colour you actually bought will appear.
Next Steps
We stock slate chippings in blue, grey, plum and green, with nationwide delivery, alongside the MOT Type 1 and membrane the groundwork needs. Measure up, run your numbers through the gravel calculator, and browse the full slate chippings range.
Have you ever laid slate chippings in a border? What went underneath, and has it stayed on the surface where you put it? Love to hear in the comments below.
FAQs
Can you lay slate chippings on concrete?
Slate chippings laid loose on concrete skate about underfoot and migrate off the slab, because there is nothing for them to bed into. There is nothing for the chippings to bed into, so they skate about underfoot and migrate off the slab. Inside a solid raised edge on a low-traffic area you can get away with it; for a finish over concrete that stays where you put it, the stone has to be bound to the slab, and a resin-bound gravel kit is the DIY-friendly way to do that.
How do you lay slate chippings on a slope?
A gentle fall is fine laid normally. Anything steep enough that you would notice pushing a barrow up it needs gravel grids pinned to the base and solid edging across the bottom, or gravity delivers your slate to the lowest corner within a season.
Can you lay slate chippings over grass?
Slate chippings should never go over grass; strip the turf first. Grass buried under membrane and slate dies and rots into a soft, sinking layer, so the surface dips within a year and the rotting turf feeds weed growth from below.
Do you have to wash slate chippings before laying?
Slate chippings only need washing before laying for ponds and water features, where slate dust will cloud the water. Everywhere else, lay it dusty and hose it down after, or let the rain do the job for free.
Why are my slate chippings turning white?
That white haze is efflorescence: salts dissolved from the ground and the stone, left behind on the surface as rainwater evaporates. It does no harm whatsoever. A rinse will shift it for a while, but it tends to return until those salts have worked their way out, so I leave it to the weather rather than chase it.
Will weeds grow through slate chippings?
Weeds rarely come up through slate chippings from below where a membrane is down and the slate is at full depth. The weeds you will actually meet root in the leaf litter on top, which is why an autumn sweep does more for weed control than any fabric upgrade.