With the popularity of the industrial design trend firmly established, it’s no wonder that materials that were originally cast on the factory floor – literally – are now being adopted in the home. Polished concrete is a sleek and stylish, yet hardwearing and low maintenance covering.
It can be used to achieve the luxury look of granite or marble without forking out on the hefty price tag, making it a solid solution for a self build or renovation project.
What are the benefits?
If you want a low maintenance stone appearance then polished concrete, which typically costs anything from £80 per m2 to £150 per m2, is ideal. The material works well with that self build staple underfloor heating (UFH), because it is a good conductor and will retain the heat produced.
It even stores warmth acquired from solar gain (through windows etc) and recycles it as internal temperatures cool – helping to maintain an even climate. You can also choose from a range of colours to complement your interior scheme.
Where can it be used?
Polished concrete floors are ideal for creating a seamless link between inside and out, especially when connecting a kitchen-diner with the garden. The light – reflective and robust material will hold up well in high traffic areas, which is why you’ll find it on many shop floors. Depending on its condition, it may be possible to polish existing concrete, which is common in basement conversions or when transforming warehouses and industrial structures.
It’s generally easiest to install in a new build project, where you can plan for an arrangement that supports the weight of the material. However, a retrofitting scenario is also possible. When applying concrete retrospectively you will need to consider whether the floor structure can take the extra weight (around 200kg per m2). You should also allow for the fact that the ceiling height within an existing property will be reduced by a least 100mm.
Concrete is made by combining cement, gravel, sand and water. The mixture is then usually poured onto a steel and fibre-reinforced mesh, which minimises the risk of cracking.
If you’re fitting UFH, the concrete should be installed on top of the pipes. Either way, it will then be levelled and compacted using internal or external vibration to remove any air pockets and surface voids, which could reduce the strength and durability of the material.
Depending on your desired finish, a plain or coloured hardener (known as a dry shaker) is added to the surface of the concrete. This is smoothed in using a power float machine, which features a large round flat disk, for rough grinding the concrete. This can be repeated between four to eight times to achieve the desired effect.
It’s crucial that the treatment starts when the concrete is hard enough to hold the weight of the machine and the operator, but not so dry that the power floater cannot trim the high spots or fill the lows effectively. Most polished concrete floors are cast in one section, temporarily covered and left to cure, which is a much faster process in the warmer months. After a month the concrete is uncovered, cleaned, mopped and burnished to remove any inconsistencies or footprints. At this point some companies will simply apply a matt, satin or gloss sealant to achieve the desired appearance.
Technically a true polished concrete floor is created by using a diamond grinding machine that evens out the surface, which is then treated with a chemical densifier to reveal a blemish-free shine. It is not considered polished concrete until a level of 400 grits is reached to achieve a glossy finish.
What to consider
At least 28 days must pass before freshly poured concrete can be polished. However, works such as kitchen installations can continue. It will be 6 -12 months before the concrete truly reaches its full strength, but the floor will be usable much sooner.
Sudden temperature change is the biggest reason for cracks in floors. However, as well as the reinforcement mesh that’s laid before the concrete is poured, control joints can also be cut into the concrete surface at predetermined locations. This creates a deliberate weak spot so the polished concrete will shrink (crack) in a neat straight line to look like tiles and avoid breaks elsewhere. The joints should be added with a neat saw within 24 hours of installing the concrete.
Photo: The owners of this terraced home in London wanted to establish a striking, yet low-maintenance space for their young family. Their project, designed by Architecture for London, involved adding polished concrete flooring, which runs from the living space straight out to the courtyard-style garden to offer a durable connection between indoors and out.
First published: August 2015