Board Formed Concrete Worktops and Buildings
Board formed concrete was the original ‘go to’ process back in the day when concrete was really taking off as the material of choice for architects. Also known as ‘shuttered concrete’ it was originally specified due to its economical cost, sustainability and ease of use.
This method refers to the process of when the structural concrete is poured against rough textured wood (such as ply or regular timber planks). Forms could easily be assembled by a team of carpenters and pieces re-used as and when needed. Originally, not much thought was given to the aesthetics of the concrete as it was purely considered practicality.
Eventually, some keen-eyed architects saw the poetic potential of eternalising the markings of nature by setting them in stone, essentially building wooden structures out of rock!
Looks easy… right?
It may seem like an easy process to achieve this look, to simply pour the concrete against some rough sawn wood, let it set and – hey presto! Lovely board formed concrete worktops. The reality, however, is much different. If the wood is not prepared properly, the wet concrete will find its way in and stick so hard that when it comes to striking the moulds you will have chunks of the face remaining on the wood and vice versa, along with a very discoloured finish. Another common problem is that un-prepared timber or ply will quite often be a little too smooth for the textures to telegraph through properly.
How we did it
To retain the lovely rough and earthy qualities of the wood and avoid any sticking, we first had to expose the grain and emphasize the peaks of the slow-growing hard winter growth vs the peaks from the soft summer growth. This was done by sandblasting the surface to remove the softer parts and reveal the stronger.
Once the desired amount of grain had been accentuated, we then moved on to sealing the surface with a polyester resin. After a couple of coats had been applied and well dried we then waxed the finish ready for casting.
The concrete was then mixed and poured into the forms. We vibrated the actual worktop pieces to minimise the number of air pockets on the top face of the concrete worktop. Nobody really wants to have voids on the top face of food prep surfaces (although we have been asked before) as they will inevitably be harder to keep clean. The edges, however, were hand packed to give a few air pockets and lay-lines here and there. This creates a bit of industrial realism and helps to portray the honesty of the materials used.
Natural, well-graded river sand was chosen as the aggregate. This was combined with white cement and a white pozzolan called metakaolin. Choosing white cement as the base ensures the sandy colours of the aggregate will show through once polished and sealed. For this project, the client chose a highly polished top to give a stunning contrast from the rough edges.
And voila – here’s the finished product:
Note the wood pattern in the rough sides of the concrete worktop.
A polished concrete worktop works with the rest of the modern kitchen.
You can see more pictures of this project on the dedicated board formed concrete worktops case-study page.
Board Formed Concrete in Architecture
While I used board formed concrete to make interior units like polished concrete worktops and concrete sinks, the method is employed by builders and architects the world over to apply this stunning effect to a building’s exterior.
While concrete buildings were all the rage in the ’70s, they have been phased out over time… although the style is certainly making a comeback in modern architecture.
There’s a fantastic piece by Bob Borson in which he gives a detailed step-by-step guide to how he used board-formed concrete in a building project.
Many brutalist buildings still stand with these hallmark concrete textures, arguably the most famous of which is the Southbank building in London. Baltic pine was used and meticulously constructed with the accuracy and precision of finishing carpenters. The end result is a symphony of modernist rising cuboids, organic mushroom columns and cantilevered floating floors adjoined with the iconic curved stairwells.
During the ’80s and ‘90s the use of steel and plastic forms gained popularity and so the board formed concrete effect was quickly superseded. Buildings were now smooth if the ‘naked’ structural element were to be on the show. The phrase ’Concrete Jungle’ was born and the mass populous agreed that concrete was now ugly! Many buildings at this time were being clad in decorative panels like metal or phenolic board. As with most trends, however, things will come and go, what is considered ‘cool’ one day will seem dated the next.
Many people thought the Southbank national gallery was an eye-sore when it was first built, in fact, it was crowned ‘The ugliest building in Britain’ by a Daily Mail poll. People during this era certainly agreed the brutalist architecture movement was ugly and dystopian, as so many have been demolished or clad over in the subsequent decades.
Thankfully though, some of the great iconic structures have remained to be cherished. The board formed concrete look has now enjoyed a revival and come full circle. It has risen through the ranks from ugly to beautiful, from dystopian to chic. Something that will never go in or out of fashion but now widely considered as a timeless design classic.