How to lay a concrete garage base?

UK Home Improvement

How To Lay A Concrete Garage Base?

Knowing how to lay a concrete base for a garage is vital to the longevity of the structure. The stability of any building starts with the base or foundations, and a concrete garage base is no different.


You can make your life a lot easier by making sure you choose the location of your new garage carefully. Don’t just check there is enough space on the ground, look up and make sure there is enough height available for the whole structure. Looking at things like drainage and checking your finished garage won’t block all the light to a previously sunny garden is also something to consider.

Before you start laying a concrete garage base, make sure you spend enough time planning ahead and preparing the site. Making sure the ground is as level as possible will make the whole process much more straightforward.

Understanding the different concrete floor layers

When learning how to lay a concrete garage base, you’ll need to be familiar with the different layers you can add to your concrete slab, and why you need to include them.

Infill and base layer

Once you have excavated a suitable area for the garage concrete base, you’ll need to make sure it is compacted and level. If you start with a compacted, level base then it will be much easier to ensure the uniform thickness of your slab. Adding an infill layer of sub-base will help to create a stable and level surface to start with.

Excavate at least an extra 100 mm to allow for your sub-base layer. Compacting the sub-base helps to remove any gaps between chunks of material and ensures that your slab is evenly supported.

Recycled concrete is an excellent material to use as a sub-base, there are lots of different grades available as well as other aggregates that can be used for a variety of uses.

Damp-proof membrane (DPM)

Adding a damp-proof membrane underneath your concrete garage base helps to prevent damp from rising through the slab. This is especially important if you are building in an area prone to being damp.

Before laying the membrane, cover the sub-base with a layer of sand, this should stop any sharp edges from puncturing the membrane. It’s important to slightly overlap the sections of the membrane so the whole area is covered, this will ensure the slab dries at the same rate and will prevent cracking from uneven curing.

You can also add a layer of membrane between the slab and the bottom of any walls it might be next to, this prevents any damp transferring to the wall.

Concrete layer

The minimum thickness for a concrete garage base is 100 mm, laid over a sub-base of at least the same thickness. You will need to find out more information on the strength and grade of concrete you can use depending on how deep your concrete base needs to be.


Reinforcing your concrete garage base with steel mesh can help to strengthen the slab, this is particularly important if you are constructing a very heavy garage, or if the slab will need to hold heavy machinery. 


You’ll want to know how to build concrete forms, to get everything in place ready for your concrete to arrive. Next, it’s time to pour the concrete.

For larger projects like garage bases, it would be extremely time consuming to mix concrete by hand. Our readymix concrete is delivered directly to your site, ready to pour. Pump hire can also be useful if the garage base isn’t easy to access.  

Start pouring your concrete in layers, working quickly and methodically as concrete will start to cure within two hours of being mixed. Make sure you pour concrete right up to the edges of your formwork and into the corners, filling until the concrete is just proud of the forms. Tap the edges of the formwork and tamp down the concrete to remove any air bubbles.

Then you’ll need to level and strike-off the slab, this is done by moving a straight piece of wood over the top of the concrete and the formwork to level it. Using a side-to-side or sawing motion across the whole slab to remove any excess concrete.

Next, by using a specialist tool called a darby or a bull float, you will need to smooth the surface of the concrete garage base. This will reduce any higher spots or gaps remaining after striking off. It is also recommended to shape the edges of the slab so water can run off and away from your finished structure.


Before removing the wooden formwork, leave the slab to cure for at least three days. It may take longer if the weather is particularly cold. Avoid walking on the slab for at least three or four days, then wait until ten days have passed before starting to add your garage structure.

Concrete takes up to 28 days to reach full strength, during which time it continues to cure and harden.

Advice on laying a concrete garage base

Whether you are laying a concrete garage base or a concrete path you’ll find lots of helpful advice on our blog about some of the most common concrete projects.


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