Ground Preparation

The most important step in this guide is to make sure you have prepared the site correctly for us to deliver your concrete. The total floor area must be accurately measured so that you know how much concrete to order, but don’t worry if you’re a little bit out… that’s the beauty of ordering volumetric concrete.

The surface area is measured by Length x Width x Depth. Remember to allow additional depth for both your sub base (roughly 100mm) and your damp proof membrane. Please use 365 Concrete’s Free Concrete Calculator if you need help.

If you are building on a pre-existing soil base the ground must be compact with all stones, plant material and debris completely removed. A solid, compact ground helps you achieve a smoother concrete surface without cracking.

TOP TIP: Hire a mechanical excavator for this process. Providing access is available, this will save you time and labour.

Do I Need An Aggregate or Hardcore Base Layer?

A crucial component of any concrete flooring is a good base layer of crushed aggregate, also known as hardcore. After you’ve laid and compacted your sub base, place your damp proof membrane (D.P.M or Vapour barrier), making sure the making sure that you have the edges facing upwards, essentially making a tray area for the concrete to be poured into.

Having a D.P.M protects your concrete flooring from encountering any sort of chemicals from the earth or rising damp and will also stop your concrete from drying out too quickly and cracking. Expansion joints allow independent movement between adjoining structural members, minimising cracking when such movements are restrained.

Place joints around 30 times the slab thickness apart. So, for a slab which is 100mm thick, the joints should be placed around 3 metres apart. Make sure joints are cut deep enough, they need to be at least a quarter of the thickness of the slab. For a 100mm slab, cut the joints at least 25mm deep.

TOP TIP: The total compacted hardcore thickness should generally be in the range of 100–600mm. Fill should be placed and mechanically compacted in layers not exceeding 225mm deep to form a stable mass. Standard concrete floor slab thickness in residential construction is 4 to 6 inches.

What Reinforcements Do I Need For My Concrete Floor?

Depending on what kind of weight load your concrete floor is going to be bearing, the type of reinforcement needed will vary. For domestic projects such as house floors, the average weight load will be low. A simple steel mesh will suffice in this instance.

For a Commercial project, reinforced steel (Rebars) are a must in most cases. Again, this will vary depending on the size of the commercial property. For a larger area, first you must get a Structural Company to asses the area and inform you of what reinforcement you will need. For smaller areas using roughly 10 Rebars at a distance of around 600mm apart will strengthen the concrete enough.

TOP TIP: For the rebar to be most effective, it needs to rest in the middle of the slab, not on the bottom. That means that it needs to be anchored in the ground well enough to hold its position when the concrete is poured.

What Concrete Strength Do I Need?

Getting the mix strength right is essential in any application. With the use of our Volumetric Concrete mixers, all of our concrete is mixed on-site meaning that it is always freshly batched, making it easy to pour, place and finish. This process is usually finished using a Concrete Float to smooth out the concrete floor surface. For an internal domestic concrete floor, we recommend using a C20/25 concrete mix, see our full guide to concrete strengths.

TOP TIP: Use a tamper board to pat the concrete repeatedly, moving in a straight line down one section of the formwork at a time. You only need to apply a moderate amount of pressure at a time and dip the tamper into a bucket of water occasionally, so it doesn’t drag on the wet concrete.

What Kind Of Concrete Aftercare Do I Need?

After the concrete has been poured and finished, you must cure the concrete. It is important that the concrete doesn’t dry out too quickly as it hardens, it needs to retain water to fully hydrate all the cement and result in a durable concrete. The easiest way to achieve this is to keep the slab moist by covering it with polythene sheeting or a damp hessian.

You can walk on concrete after 48 hours but, ideally leave it for at least five days. Formwork can be removed after 24 hours, although it is best to leave it for 72 hours to avoid any possible damage to the edges of the new slab. The concrete will take 28 days to reach its full strength.

TOP TIP: During particularly cold weather waterproof glass fibre or mineral wool insulation blankets can be placed directly on the freshly placed concrete, water should not be used to cure during cold weather. During very hot weather provide wind shields to cut down air movement and minimise loss of water.