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How to lay paving slabs on concrete

How to lay paving slabs on concrete

How to lay a patio on concrete

Many people assume that laying paving slabs on concrete is a difficult task and one that’s
better left to the experts. But arm yourself with the right tools and know-how and you can
create a patio that beautifully enhances your garden.
Whether you’re mixing the concrete yourself or laying paving on existing concrete, we’ve put
together this step-by-step guide to show you how it’s done. Follow our tips for a durable and
attractive outdoor space that will give you years of pleasure.

Quick guide: Laying patio slabs on concrete

1. Mark the area
2. Dig a bed that’s 105mm deep
3. Add a 50mm sub-base layer
4. Mix the concrete – one part cement to six parts ballast
5. Add a 30mm layer of concrete mix
6. Lay the paving slabs, leaving 8 to 10mm spaces between them
7. Fill the joints with the mortar mix

What tools do i need?

  • Mattock and shovel
  • Flat screeding tool
  • String and stakes
  • Wheelbarrow or board for mixing
  • Spirit level
  • Rubber Mallet
  • Protective Gloves
  • Knee Pads
  • Tape Measure
  • Rake
  • Garden Roller or tamper
  • Plate Compactor
  • Brick jointing tool

What materials do i need?

Laying patio slabs on concrete guide

Mark the area

The first thing to do is to decide exactly where you would like your patio. It’s worth
considering which areas of your garden are shaded – and whether you want to avoid
them – and which might provide the most privacy.
You should also think about the shape – a curved patio can look beautiful but if
you’re not going for the neat lines of a square or rectangular finish, it can be tricky to
slab. It’s also important to consider what you’ll be using your patio for. Will it be for
entertaining, to provide space for an outdoor kitchen, or simply to act as a walkway or
entrance to your property? All of this will determine the size and style of your patio.
Decisions made, you’ll then need to mark the area using string lines and pegs. Once
done, make doubly sure its proportions are right for the garden and house.

Dig a bed

Working slightly outside of the area you’ve defined with the string lines and pegs, dig
a 105mm bed. It’s important to remember that the finished surface level of your
completed patio should be at least 150mm (two house bricks) below any adjacent
damp proof course.

Check that the centre of your site is level with the edges and isn’t rising up or dipping
down. Use a spirit level to ensure it’s as flat as possible.

Add the sub-base layer

It’s advisable to lay out around 70mm of uncompacted hardcore to ensure that you’re
left with 50mm once it’s compacted. Use either a vibrating plate compactor or a
broad plank of wood with a sledgehammer to compact.

Mix the concrete

You can use a sturdy wheelbarrow to make up your concrete mix, as this way it’s
easier to move and dump it, but you might prefer to use a mixing board. You will
need to mix one part cement with six parts ballast and check the bag for a starting
point as to how much water you’ll need.

It’s a good idea to add the water gradually so you can judge the consistency. Too
little water and it won’t mix, too much and it will weaken the mixture. Pull and mix it
using a flat shovel or spade.

The concrete should be of a consistency that means it can be poured thickly – if it’s
crumbly then it’s too dry and if it’s runny it means it’s too wet.

Lay the concrete bed

Add 30mm of your concrete mix to the site and screed it to ensure everything is
packed down and levelled off. It’s important you tamp it down to push the coarse
aggregate in the concrete below the surface and consolidate the concrete. This
ensures there are no gaps left and water cannot enter and cause damage later on.

Laying the slabs

Now it’s time to start laying paving slabs on your concrete. It’s a good idea to wear
knee pads and gloves for this to avoid potential burns from the wet cement. Whether
you’ve chosen marble, sandstone or concrete paving, carefully to lower your first slab
into the concrete.

Keep adding the slabs and ensure there’s a gap of about 8 to 10mm between each
stone. Don’t walk on the slabs once they’re laid – you need to wait for the concrete to
set, which should take around 24 hours.

Fill the joints

Once the cement has set, you can create the mortar mix. Use four parts sand to one
part cement and water – you’re looking to get it to a firm consistency. Fill the gaps
between the slabs with the mix and use a brick jointing tool to pack it in and create a
nice smooth finish. Take care not to get mortar on the face of the slabs as this can
stain them.

Concrete is fully cured after 28 days – this is when your new patio will be at its full
compressive strength. However, the advice is usually to avoid walking on it for at
least 24 to 48 hours to allow it to dry and strengthen and become the beautifully laid
patio you’ve put so much effort into.

Laying paving slabs on existing concrete?

Alternatively, you might already have a concrete base in place. If that’s the case, laying
pavers on concrete shouldn’t take you too long.

Quick guide: Laying a patio on existing concrete

1. Prepare your concrete
2. Prime the back of the flags with a cement-based primer
3. Create the mortar mix – add a 30mm layer
4. Lay the paving slabs, leaving 8 to10mm spaces between them
5. Fill the joints with the mortar mix and leave to set

What tools do I need?

  • Hard-bristled brush
  • Flat screeding tool
  • Wheelbarrow
  • Spirit level
  • Rubber mallet
  • Protective gloves
  • Tape measure
  • Brick jointing tool

What materials do I need?

In detail: Laying pavers on existing concrete

Prepare your concrete

Use a sweeping brush – and a hose pipe if necessary (although bear in mind you’ll
need to let it dry afterwards) – to make sure your concrete surface is smooth and
clean before you start. Check for any flaking or loose bits and remove them.

You’ll need to ensure there are adequate falls in place to allow surface water to drain
off, and the finished surface level should be at least 150mm (two house bricks) below
any adjacent damp proof course.

Prime Time

Spread a cement-based priming product on to the back of the slabs. This will ensure
they’re laid as securely as possible.

Mix the mortar

Using four parts sand to one part cement and water, create a mortar mix. Take care
to add just the right amount of water for a firm consistency – it should be damp, but
not wet and runny. Put down a 30mm layer of the mix and ensure you have an even,
smooth base, ready for your slabs.

Lay the slabs

Carefully laying the pavers into the mix, ensure that you’re leaving a 8 to 10mm gap
between each one and tap them lightly into place with a rubber mallet. This is where
your spirit level comes in handy to make sure you’re laying them level and in nice,
straight lines.

Fill the joints

Put the finishing touches to your project by using the mortar mix to fill in the spaces
between the slabs. Use a brick jointing tool to pack it in and create a smooth finish,
taking care not to get mortar on the face of the slabs – you don’t want to be left with
permanent stains that will ruin the overall effect of your hard work.

You’ll need to leave the paving to set for at least 24 hours before walking on it (or
longer in wet weather).

Prefer to have your patio installed by an expert? Get in touch today or click here to find your
nearest Marshalls-accredited installer

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