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The quick answer
- Heavy builds (block BBQ islands, brick pizza ovens) need a concrete slab.
- Lighter builds (modular kitchens, a BBQ on a stand, a gazebo) are usually fine on a well-laid patio.
- The sub-base matters most: dig out, lay MOT Type 1 hardcore and compact it properly with a hired plate compactor.
- Hire, don't buy: a mixer, compactor and block splitter for a weekend cost far less than buying them.
- Allow curing time: give a concrete slab at least a few days before you build on it, longer in cold weather.
Whatever you're building in the garden, the base is the part nobody sees and the part that decides whether it lasts. A block-built BBQ island or a brick pizza oven weighs a lot, and if the ground underneath moves, blocks crack and worktops tilt. I built my own composite deck, so I know how much of a garden project is groundwork you never see again. This guide covers the two common options in UK gardens, and how to do each one properly.
Concrete slab or paving?
| Concrete slab | Paved patio | |
|---|---|---|
| Best for | Block or brick BBQ islands, brick pizza ovens, heavy masonry | Modular kitchens, freestanding BBQs, gazebos, seating areas |
| Strength | Very high, spreads heavy loads | Good, if the sub-base is right |
| Looks | Plain, usually hidden under the build | Finished surface you walk on |
| DIY difficulty | Medium: hard work on pour day | Medium: slower, more fiddly |
A common approach is both: a concrete slab under the island itself, and paving around it for the cooking and seating area. If you already have a patio, check it first. If the slabs are level, don't rock, and don't sound hollow when you tap them, you can usually build a light structure straight on top. For a heavy block island, lift the slabs where the island will sit and put in a proper slab.
Tools and materials
Most of the heavy kit is only needed for a day or two, so hiring makes far more sense than buying.
Tools to hire for the job
- Electric breakerBreaks up old slabs or concrete where the base will go.Hire from HSS
- Mini diggerOnly worth it for big areas or awkward ground. For a small island footprint, a spade and a mattock are usually enough.Hire from HSS
- Plate compactor (wacker plate)The one tool you really shouldn't skip. It compacts the hardcore so the base doesn't settle.Hire from HSS
- Cement mixerFor mixing concrete for a slab, or mortar for laying slabs and blocks.Hire from HSS
- Block splitterCuts paving and blocks cleanly without dust.Hire from HSS
Hire prices vary by branch and hire length. Many tools can be delivered or collected from a local branch.
Materials
- MOT Type 1 hardcore (sub-base)
- Ballast and cement, or ready-mixed concrete for larger slabs
- Timber for formwork, plus pegs
- Sharp sand and cement for bedding paving, or slabs and jointing compound
- Optional: steel mesh (for larger slabs) and a damp-proof membrane
Hand tools
Spade, mattock, wheelbarrow, rake, long spirit level, string line and pegs, tape measure, a straight timber for levelling, rubber mallet, and PPE (gloves, goggles, FFP3 dust mask and ear defenders).
How to lay a concrete slab
- Mark it out. Peg out the footprint of the island plus about 10cm on every side. Check the diagonals are equal so it's square.
- Dig out. Remove turf and soil to about 20–25cm deep for a typical island. Go deeper on soft or clay ground. Break up any old concrete in the way with a breaker.
- Build the formwork. Fix timber boards around the edge with pegs, with the top edges level. This sets the height and shape of your slab.
- Lay the sub-base. Spread about 10cm of MOT Type 1 and compact it with a plate compactor. Do it in two layers of around 5cm, going over each layer several times.
- Mix and pour. Mix concrete in a cement mixer (or order ready-mix for bigger slabs) and fill the formwork to about 10cm thick. Work it into the corners.
- Level it. Drag a straight timber across the top of the formwork in a sawing motion to level the surface. A very slight fall helps rain run off.
- Let it cure. Cover it to protect it from rain, frost and hot sun. Leave it at least a few days before building on it. Concrete keeps gaining strength for weeks.
How to lay paving for a kitchen area
- Plan the fall. Patios need a slight slope away from the house so water drains off. Around 1 in 60 to 1 in 80 is typical.
- Dig out and compact. Dig deep enough for about 10cm of hardcore, plus the bedding mortar and the slab thickness. Compact the hardcore with a plate compactor.
- Lay on a full mortar bed. Bed each slab on a full bed of mortar rather than spots of mortar, which leave hollows. Tap it down with a rubber mallet and check it with a level.
- Cut neatly. A block splitter cuts most paving cleanly without dust. For porcelain, use a wet cutter or a specialist disc.
- Joint it. Once the bedding has set, fill the joints with mortar or a jointing compound.
Mistakes to avoid
- Skipping the compactor. Hardcore that hasn't been compacted settles over time, and so does everything on top of it.
- Building too soon. Give the concrete time to cure before you load it with blocks.
- No fall. Water sitting on a base or patio freezes and causes damage in winter.
- Building over drains and inspection chambers. Keep access to them clear.
- Forgetting services. If you'll want gas, power or lighting at the island later, lay ducting before you pour.
Handy kit from Amazon
- FFP3 dust masksFor cutting, breaking and mixingView on Amazon
- Long spirit levelChecks the formwork and slabs are levelView on Amazon
- Rubber malletBeds paving slabs without damaging themView on Amazon
- Heavy-duty work glovesProtect your hands from cement and hardcoreView on Amazon
As an Amazon Associate I earn from qualifying purchases.
Next steps
Base done? Move on to building the BBQ island, and check outdoor kitchen costs in the UK to budget for the rest.
Frequently asked questions
How thick should a concrete base be for a BBQ island?
For a typical garden BBQ island, about 10cm of concrete on about 10cm of compacted hardcore is a common approach. Go thicker on soft ground or for very heavy builds, and get advice if you're unsure.
Do I need a concrete base for an outdoor kitchen?
For block, brick or stone builds, yes. Modular steel or freestanding kitchens are usually fine on a sound, level patio.
How long before I can build on a new concrete slab?
Leave it at least a few days before you start building, longer in cold or wet weather. Concrete keeps getting stronger for several weeks.
Should I hire or buy a plate compactor?
For a one-off garden project, hire one. You'll usually only need it for a day, and hiring is far cheaper than buying.
Home cook, keen DIYer and long-time website builder, writing practical outdoor cooking guides for UK gardens. More about me.