How to lay concrete sleepers as stepping stones?

kristina1

Hello,

Our small courtyard currently has a pathway alongside the house that comprises astroturf on top of quite an uneven layer of crushed rock, which I think was originally compacted but is now crumbling at the edges and in particular areas. Underneath the astroturf and crushed rock layer is a layer of black plastic weed control mat, and beneath that is heavy (and also uneven) clay.

Here's a pic of it currently (with a bunch of pot plants / corten raised bed I haven't yet installed – ignore those for now!):

I'd like to replace this with a pathway made of staggered concrete sleepers as stepping stones, with gravel in between the sleepers, similar to this pic:

This is my current general plan to achieve this – and the questions I have about it:

1. Pull up the astro turf, dig up (and keep) the crumbly aggregate/crushed rock, pull up the weed mat and dig into the clay a bit so I can even the clay out a bit.

Question 1: Do I need to put weed mat back in on top of the clay? I prefer not to use plastic in the garden but there are currently some small roots growing underneath the existing weed mat in one corner so wonder if it's a good idea to keep it?

2. Lay the old aggregate/crushed rock down on top of the clay layer, likely with some extra purchased crushed rock if I need a greater volume. I'd then compact this down – I'm planning to borrow a plate compactor from the tool library.

Question 2: Is it ok to reused the existing crushed rock or is that a bad idea? If so, should I replace it with crushed rock or with road base instead?
Question 3: What thickness should this layer of compacted crushed rock or road base be?

3. Lay out the concrete sleepers. The minimum size of the sleepers I want to use is 1.2m x 200mm x 75mm and I believe they weigh about 40kg each. I will likely also use some 1.5m and/or 2m long sleepers in a wider part of the area.

Question 4: Would I need to use mortar to fix the sleepers in place?  

4. Top up the gaps between the sleepers with gravel.

Keen to have any insight into my questions, and also to hear if I've missed anything critical in my planning / thinking about this!

Thanks so much,

Kristina

MitchellMc

Welcome to the Bunnings Workshop community @kristina1. It's sensational to have you join us, and many thanks for your question about laying concrete sleepers.

You don’t necessarily need to reinstall weed mat, especially if you’re trying to avoid plastic in the garden. However, since you’ve already noticed some root growth under the existing mat, it could be worth considering a biodegradable option like carpet or a thick layer of cardboard, or simply relying on a well-compacted base layer to reduce weed growth. Just keep in mind that no solution is completely weed-proof, so some occasional maintenance might still be needed.

Reusing the existing crushed rock is absolutely fine, as long as it’s clean and free from soil or organic matter. If you need to top it up, consider using road base rather than crushed rock alone, as it compacts better thanks to the mix of fine and coarse materials. For a stable base under your stepping stones, aim for around 75–100mm of compacted material. Lightly moisten the base as you go and use a plate compactor to ensure it sets firmly—particularly important when building over clay.

When it comes to laying the concrete sleepers, you won’t need mortar to keep them in place. Their weight alone should hold them steady if they’re sitting on a well-compacted and level base. If you’d like extra stability or are concerned about movement, you could bed them into a thin layer of sand and cement mix, but it’s generally not necessary for a path like this.

Once your sleepers are set, you can top up the spaces in between with gravel. Just make sure your stepping stones are all level with each other and at a comfortable walking height. If you're using different lengths of sleepers, plan the layout ahead of time to ensure a balanced look.

Please let me know if you have any questions.

Mitchell