Exposing concrete as a feature (‘fair-faced concrete’) is not a novel idea — architects practising modernist and brutalist architecture in the early to mid 20th century were well versed in the art. But for most homeowners, concrete remained a material best left concealed.
In the 21st century, however, this material is now making its way into more and more interior schemes from worktops, fire surrounds and even baths, to polished flooring and entire walls in concrete. It’s no longer just the preserve of industrial-style, minimalistic interiors either — the Béton Brut aesthetic (Le Corbusier’s coinage for exposed concrete) is no longer so brutal. Instead, it’s increasingly being used as a raw counterpoint to warm, natural materials such as timber.
“There’s been a big resurgence in concrete, particularly with increasing possibilities for colour and texture,” says architectural concrete consultant David Bennett, who is author of numerous books on the topic, including the definitive title Sustainable Concrete Architecture.
“Architects and self builders are increasingly recognising the important role fair-faced concrete can play in creating a PassivHaus or eco home, too,” says concrete specialist Jonathan Reid of GreyMatter Concrete. There will be more on sustainability later, but what else do you need to know if you plan to work concrete into your design?
Broadly speaking, fair-faced concrete can be created in one of two ways: it can be poured in-situ on site or ‘precast’ off site. Precast concrete, being a factory-produced and finished product, possesses a greater degree of uniformity in terms of colour, texture, finish, etc.
That said, the thing about concrete is that no two surfaces are exactly the same. This is a big positive for most, but it can also be a downfall.
“The biggest issue surrounding specification is expectation. Self-builders considering a concrete floor or wall really should look at at least two other examples first,” says Jonathan Reid, who also advises contacting the Concrete Centre, talking to specialist contractors and attending seminars such as those at The Building Centre, London.
“It can be an uncompromising material, and can take some adjusting to. It’s also a good idea to talk to homeowners with concrete floors, walls, etc., and ask ‘what is it like to live with?’,” continues Jonathan Reid.
When it comes to in-situ walls, board-formed or shuttered concrete offers the opportunity for some very different finishes. Other benefits of the in-situ method include the flexibility to use it on small sites (possibly where access is limited).
“With in-situ concrete, you’re not just creating one monolithic; there’s variation in colour and texture,” explains David Bennett. “Concrete is liquid stone — with knowledge, patience and skill it can be made into an endlessly creative product that can be worked while the surface is still soft and active or cast in moulds to harden.”
Shuttering or formwork (a mould) is constructed on site, typically out of timber boards or steel, and then concrete is poured and left to cure. Once removed, the imprint of the formwork is left on the surface. This looks particularly striking when timber is used. This timber can then be reused – perhaps for flooring – which cuts costs and reduces the embodied CO2 of the building.
A shuttered concrete wall, imprinted with characterful wood grain, is a defining feature of this PAD Studio self build. The wall was constructed under the guidance of David Bennett who advised that a Keim finish be applied to prevent water penetration
- Bracing the formwork to ensure it’s strong enough.
- Make sure you whoever is doing the work gets the concrete mix right.
- Good pouring — poor workmanship here can lead to cosmetic and even structural defaults.
- Sealing concrete is another consideration.
“Sealing is optional, but where concrete is going to be subject to moisture (i.e. external walls or wetrooms), or to stains, then it should be applied,” says David Bennett. “It needs to be a breathable coating or sealant. If it is not breathable, the top surface will begin to blister and break down as the concrete cures and dries out.”
As such, it’s a skilled art, and a job best left to a specialist. For smaller projects (such as in-situ worktops), courses held by David Bennett Associates and The Building Centre can educate architects and builders on the topic.
One of the benefits of precast concrete for self build is the ease, precision and speed of construction on site.
“Precast concrete is not really suited to refurbishing houses or building basements, though,” says David Bennett. “It only becomes economical when there is a lot of repetition and reasonable lead time is allowed to factory-produce the elements.”
For homeowners who want an element of concrete, without an entire wall, or perhaps want to replicate the look in an existing home, then precast wall panels are a good solution. Glass-reinforced concrete (GRC) is often used here for its lightweight properties. (It’s worth noting, too, that with less concrete, the panels’ ability to act as a thermal store will be reduced).
Lightweight PANBETON® custom-made wall panels, by Concrete by LCDA, clad this contemporary fire surround. They are available in the UK at Holloways of Ludlow
Worktops are one area of the home where concrete is really taking off. Again, worktops can be precast (there’s usually a good deal of heavy lifting involved in installation, though), but are usually cast in-situ.
Jamie Telford, director of Roundhouse, explains the process behind their in-situ worktops: “Our bespoke concrete worktops are cast in-situ, mixed and poured on site, and then left to set prior to polishing, with the process taking around 28 days. Each worktop is unique — the patina is achieved as a result of the process and can’t be ‘manufactured’. Casting in-situ means that it just flows into place, so work surfaces are in a single seamless piece without joins.
This Roundhouse Urbo bespoke kitchen combines a warm driftwood veneer counter base with an industrial-style polished grey concrete (cast in-situ) worktop. Prices start at £35,000
Concrete is tough and wear, tear and age improve the patina, but it needs to be carefully looked after:
- Acid spills will stain
- Limescale-based cleaners dull the surface
- Stains can be diffused with careful polishing with a diamond pad.
Concrete’s capacity to act as a thermal store is a particular benefit to the sustainable home. A solid concrete wall or floor can be designed to absorb solar heat and slowly release it when temperatures drop, helping to regulate internal temperatures. This application can lower the heat demand of a home.
The lifecycle of concrete – the energy and greenhouse gases produced during the manufacture, transportation, installation, use, maintenance and disposal or recycling of a building material – is a key consideration, too. While manufacturing is an energy-intensive process (although the industry has worked hard to reduce CO? emissions here), transportation, compared to other building materials, isn’t with (on average) a ready-mix concrete supplier around 10 miles from any site in the UK.
Recycled aggregate and ground-granulated blastfurnace slag (GGBS) is being used more and more, which also improves concrete’s eco credentials.
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There have been a handful of self builds which have embraced concrete wholeheartedly — one such architectural gem is this award-winning individual home designed by Adrian James Architects. The self builders behind this project wanted a material which would form the structural envelope – walls, floors and stairs – and be self-finished on the interior; they also needed a construction method which would maximise potential on the tight urban plot.
The solution was precast concrete; more precisely a cross wall system crafted off site by Cornish Concrete Products, with the panels slotted into place on site within days. Even the precast staircase (above) was craned into place. Blowholes were filled with grout and the concrete was sealed in Keim, an invisible protective coating which protects the concrete from damage, decay and discolouration, and prevents dust from the concrete gathering internally.
One particular design challenge, however, was where to place service runs — the ingenious solution was a central service duct, which spans the height of all three floors, together with dropped ceilings. Full-height glazing on the rear south-facing façade (below) means the concrete acts as a thermal store, regulating internal temperatures.