How Much Does Concrete Expand?

… and other questions!

Concrete floors are increasingly popular for new build properties and renovations too.

And no surprise when you consider the hygienic, long lasting flooring solution it offers you.

Relatively simple to install, concrete floors are structures that can offer durable flooring – if they are laid properly – and this is where expert help and advice comes in.

Do you need an expansion joint?

Spend any time of websites and building forums, and you will notice a lot of discussion relating to compression, strength and expansion of concrete.

Concrete has long been used in large, scale industrial projects. For example, bridges are commonly made from concrete and you may notice that there is a joint in the top surface of the bridge. This could be in the middle or on either end of the bridge, depending on how it has been constructed.

Concrete does expand and contract – by minute proportions in most cases – and this is all to do with the moisture content of concrete.

Does concrete dry out completely?

The process of concrete ‘drying’ is called curing. The addition of water to the concrete mix is important as is the rate at which the concrete floors cures.

It may be a startling fact but concrete that is underwater will still change from its liquid state to a solid state, achieving full strength.

Thus in understanding how much does concrete expand, you need to better understand what is involved in the modern process of making concrete:

• Accelerators speed up this hydration process – the reaction of water added to the dry ingredients – thus speeding up the hardening process of concrete. This tends to be added in colder climates where the team need to lessen the time between waiting for the concrete floor to change from liquid to a hard surface.
• Retarders slow the drying process because concrete curing too-quickly as this too can be a nuisance when trying to work with concrete in its malleable state.
• Tiny bubbles in the concrete, especially that which is outside, help it to deal with the freeze-thaw cycle of cold temperatures. An agent can be added to help disperse these air bubbles through the concrete.
• In some cases, additional agents are added to make the concrete at the wet stage even more workable.
• It is also at the wet stage that any colouring agents are added too.

How do concrete floors cope with this expansion and contraction?

The movement in expansion and contraction with concrete floors that are indoors is not as obvious or noticeable that concrete outside therefore, you will be pleased to know that you will not have a large expansion joint running down the centre of your floor!

In most cases, the smallest of gaps, enough to accommodate any expansion will be left around the edge of the room. For concrete screed laid over underfloor heating systems this is an absolute must as the concrete will expand with the heat but again, this is not a massive movement.

Will concrete floors crack?

No they should not crack, certainly not in an interior installation where they are protected from weather and sudden changes in temperature.

Essentially, this is the issue when understanding how much does concrete expand. Failing to understand the expansion and contraction properties of concrete either in terms of concrete flooring inside or concrete in an outdoor situation means that it could be laid incorrectly, without room to move which will inevitably lead to cracks.

Another aspect that can lead to cracks is compression. Concrete is incredibly strong and when the correct mix is used, and laid properly, it should not crack.

The force of movement on the concrete can cause it to crack however which is why modern builders introduced steel cages into the concrete. This reinforcing cage absorbed the shock of movement, rather than the concrete itself.

Over large expanses of floor, we suggest paying careful consideration to whether a structure needs to be used to strengthen the concrete floor.

That said, once the basics are understood and followed, a concrete floor can be laid without too much trouble. Depending on the depth of the concrete, the temperature and so on, it can take a matter of weeks for the floor to cure completely – or enough for you to be able to walk on it, giving it the final top layer of treatment.

With the experienced team at Midland Polished Concrete, you can have a highly polished, glossy concrete floor installed in your home – without fuss and without compromising on its strength.