How to Lay Paving Slabs on Concrete

How to Lay Paving Slabs on Concrete

So, you’ve found the perfect paving slabs for your new patio. You’ve decided to save some money and install them all by yourself.

 The only problem is figuring out which of the multiple ways to lay paving flags is best for you and your garden. Well, we’re here to help with another in-depth installation guide, this time covering how to lay a patio on concrete.

Continue reading, below, to find out the different methods for paving over concrete, both old and new.

Option 1: How to lay paving slabs on a new concrete bed

The first installation method we’ll be covering is how to lay paving slabs on a new concrete bed. This is the option you should choose if you do not currently have a patio in your garden. With it you can start your paving project from scratch.

Continue reading below for an in-depth guide on how to lay paving over new concrete.

Preparing the new concrete bed

While laying paving slabs on a new concrete bed is more time-consuming, this method does offer more freedom in the placement of your patio. You should also lay a new concrete bed if the existing foundations are damaged beyond repair. It’s just a case of laying the right foundations for a new patio that will stand the test of time.

What do I need to prepare the new concrete bed?

Here are the 11 tools and equipment you will need to prepare a new concrete bed:

·        Measuring tape

·        Wooden pegs

·        String

·        Shovel

·        Spirit-level

·        Rake

·        Garden roller/tamper

·        MOT Type 1 sub-base

·        Cement

·        Sharp sand

·        Wheelbarrow


How do I prepare the new concrete bed?

To properly prepare the new concrete bed, follow these six easy steps:

1.      First things first, you need to measure your intended paving area, marking it clearly with wooden pegs attached together with string.

2.      Next, dig out the marked paving area to a depth of 105mm, removing any vegetation, roots, or topsoil. It’s also vital to set the gradient at a 1 in 80 fall to allow surface water to run off into drainage points. See our how to install patio drainage guide for more info.

3.      Ensure the surface is level and even using a rake and a spirit-level. Alternatively, you can use a garden roller/tamper to make this process easier.

4.      Fill the area with 70mm of MOT Type 1 sub-base and then compact it down to 50mm; ensuring it’s all level.

5.      It’s time to mix your concrete, which you can easily do by hand in a wheelbarrow. Find out more details on this method by reading our how to mix mortar for paving guide.

6.      Add 30mm of your concrete mix on top of your sub-base, compacting it down and making sure the surface is level. Preparation complete!


Laying slabs on new concrete bed

With the new concrete bed primed and ready, you can start to lay pavers into the shape of a patio. Just bear in mind that this process must be completed relatively swiftly, before your concrete base dries and hardens.


What do I need to lay slabs on new concrete bed?

Here are the eight tools and equipment you will need to lay a new concrete bed:

·        Knee pads

·        Thick gloves

·        Your pavers of choice

·        Rubber mallet

·        Spirit-level

·        Tarpaulin

·        Jointing compound

·        Hard-bristled brush

·        Slurry primer

How do I lay slabs on concrete?

Follow these seven simple steps to lay slabs on concrete without fuss:

1.      For safety reasons, we always recommend wearing knee pads and thick gloves when laying slabs into wet concrete.

2.      Lay your first paving slab in place, gently securing it to the concrete bed with a rubber mallet. Check the surface is even with a spirit-level before moving onto the next paver.

3.      Lower the next paver into place, leaving an 8-10mm gap next to the first slab. Again, gentle tap down with rubber mallet and ensure the surface is even.

4.      Repeat this process until you’ve paved over the entire concrete bed, albeit with the 8-10mm gaps between each slab. If you need to reduce the size of any awkward pavers, read our guide on how to cut paving slabs.

5.      Wait 24-48 hours for the concrete bed to dry and secure your pavers in place. If any rain is forecasted in this time, cover over the area with tarpaulin.

6.      Once the concrete bed is dry, fill the recommended joint width with mortar mix or  jointing compound if applicable, binding your pavers together.

7.      Remove any excess jointing compound with a hard-bristled brush and you’ve got yourself a brand new patio!

Option 2: How to lay slabs over old concrete

If you’ve already got a concrete base in place from an old patio, then the installation process is much quicker and easier to follow. You can also save money on the materials you would have needed to lay a new concrete base.

Find out the details on how to lay a patio on concrete below:

Preparing the old concrete bed

As the concrete bed has already been installed, this method of paving over concrete requires much less prep work. However, it’s still important that this part of the process is completed properly to ensure your patio will last for decades to come.

What do I need to prepare the old concrete bed?

Here are the four tools you need to prepare an old concrete bed:

·        Hard bristled brush

·        Sponge

·        Bucket of warm, soapy water

·        Spirit-level

How do I prepare the old concrete bed?

Take note of these three important steps for preparing an old concrete bed:


1. Start by brushing the concrete clear of debris, which includes small debris like leaves and vegetation. You also need to check for any flaking or loose concrete and remove them from the surface.

2. Next, scrub the concrete bed of any dirt or grime with a sponge and a bucket of warm, soapy water. For more cleaning techniques, read our how to clean a patio guide. Wait for the surface to dry before continuing.

3. Ensure that the concrete bed has been built for proper water drainage with gradient of 1 in 80 fall. You can find out more about fall and other essential DIY terms by reading our paving glossary.  


Laying slabs over old concrete

Once the surface bed has been cleared and scrubbed, you can get into the crux of the job: laying the slabs over old concrete. This particular method is about preparing each slab separately, so don’t worry about completing the installation within a short time period. The focus here is ensuring that the installation is finished right, not quickly.

What do I need to lay slabs over old concrete?

Before you start, gather these 10 pieces of materials and equipment:

·        Your pavers of choice

·        Slurry primer

·        Sharp sand

·        Cement

·        Water

·        Measuring tape

·        Rubber mallet

·        Spirit-level

·        Jointing compound

·        Hard-bristled brush

How do I lay slabs over old concrete?

Follow these six steps to lay slabs over old concrete:


1.      Start by painting the reverse side of your paving slab with a slurry primer, which strengthens the bond between paver and concrete bed.

2.      Then create a mortar mix at 4 parts sharp sand and 1 part cement and water (it should be damp but not runny). Lay 30mm of the mixture onto the concrete bed, covering where you’d like to place your first paver.

3.      Lower the paving slab into position, gently tapping it down with a rubber mallet. Ensure the paver is level before moving onto the next.

4.      Repeat steps 1-3 for the rest of your paving slabs, leaving an 8-10mm gap between each of the flags.

5.      Let the mortar set for 24-48 hours before brushing jointing compound into the gaps between the pavers.

6.      Brush away any excess jointing compound and, hey presto, your paving project is complete.

Need more assistance with laying slabs over old concrete?

Here at Simply Paving, we know how tricky your first big DIY project can be to complete. That’s why we always strive to offer as much guidance and information as possible to our customers, helping them get over the finish line. Head over to our Advice Centre for more how-to guides or give us a call on 0800 032 6306.

Alternatively, if you feel ready to start paving over concrete, take a look at our complete paving slabs range.

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