Bare Concrete Walls.
If you are tempted by the recent series "The World's Most Extraordinary Homes" or my argument you should maximise thermal mass you might deliberately have bare concrete walls.
Over the years only a couple of my clients buried their electrics in the concrete. Look carefully at these images for any sign of electrics, as well as making your mind up if you like the idea.
The series comprised of 4 episodes and they studied about 3 homes in each. Of the 12 or so, about half had bare concrete inside. None of them, as far as I noticed, had any of the rusty metal popular on Grand Designs in recent years.
Quite a few of the owners were architects. One of them said 'perfect architecture becomes very boring, accept mistakes'. I'm not sure I would accept the degree of mistakes I have seen sometimes.
Here are 30 or so images from the series and at the end a couple of photos selected from my work - that were never expected to be seen bare, but it shows you what might be normal using timber boards for shuttering.
I like the idea of bare concrete but I would want more variety, more timber grain and better workmanship so that there were fewer voids and less distinct lines where snots of concrete were bashed off.
At the very end I have added a couple of photos showing instances where the formwork wasn't quite right and no one did anything about it before the concrete was poured. My formwork method using timber makes it much easier not to make these mistakes.
At this junction of 4 panels we seem to have everything going on. Perhaps mastic was used between panels and the concrete later patched up.
This is a shot of the panel system. Note between the top horizontal panels and the vertical panels beneath the round waler plates on the threaded rod that goes through the wall.
This looks like they used timber shuttering with the boards in 2 directions.
In this photo you can see how they chose to fill in the holes where the threaded rods had gone through.
An electric light.
And a socket. I don't know why there is a different surface either side of where some panels were joined together. Perhaps the timber face was damaged along the edge and patched up before this wall was formed.
Or the panels might have bent back and they had to chisel concrete off where it was proud then made good, and this might be the repair we see.
Timber around the window. Perhaps that covers external insulation.
I think these vertical lines have to be something to do with spray foam or mastic between the formwork panels.
Just a bit of theory about the durability of concrete surfaces.
Concreting gangs on big sites realised long ago that if they stick the vibrating poker down between the steel and the formwork the surface would look better with fewer air holes. This is because the vibrator makes tiny pockets of air join up into bigger bubbles that float to the surface and escape - except that where bubbles come into contact with a solid formwork face the bubbles stick. They don't float. They don't escape.
Unfortunately, if the gang don't always keep the poker moving, they could vibrate the timber surface too much and that vibration can cause bleeding. That means that the vibrating formwork knocks the solid stones away, then the solid sand, then the solid grains of cement and the concrete surface against the formwork is very watery and won't get much strength. It would wear in places, such as around a light switch.
In my opinion. timber boards instead of panels are far less industrial looking and the grain far more interesting.
Deliberate use of boards of slightly different thickness.
You can get variety as well from using a mix of planed and sawn timber.
They didn't fill the gaps between the boards behind the sink with mastic or foam, neither did they knock all the snots off, creating variety with the large wall.
This ear stuck on a door made me realise they missed a trick.
Any timber board in the formwork could have anything carved into it. Where this wood is carved out, the concrete would be proud. Names, pictures, puzzles, games ..... ears.
Is the wall at the back concrete or timber? It could be concrete.
Timber and concrete side by side.
Another way of dealing with the holes left by steel threaded bars.
Looks like the vibrator did not compact the concrete in the corner. Interesting they did not bag it up, which means filling it in by rubbing in with a semi dry cement and silver sand mix.
Timber around the window opening again.
This blemish is where they emptied one lorry load of concrete and compacted the concrete. But the last of that load remains in the concrete pump tubes until a new load arrives, is discharged and pushes that older concrete out.
In this case, the next load was delayed so the concrete in the pipe began to set. When it came out it wouldn't compact properly.
The gang should have expected this and after the new concrete was coming through they should have come back with the pump, put some runny concrete on top of the old and worked it thoroughly with the poker to mix the two together and avoid this voiding.
Sometimes the voiding is a cone shape. That's when the pump pipe was above the concrete already in and dribbling slowly while waiting for the next load. That dribbling wasn't compacted.
They avoided vertical joints in this wall.
These boards were scaffold board timber without steel ends. A variety of snots, good grain and knots.
Notice the fibreglass threaded rods that I cast in to avoid leaving holes in otherwise waterproof concrete. Near top left you can see one rod has been cut off flush and you can see the thin nut that kept the forms apart.
Here you see the thin nuts doing their job.
This timber is regularised and treated 6x2. Regularised timber is often the cheapest, but the rounded edges leave a proud line of concrete.
If you use planed timber it costs a lot more money and if you are fussy about the finish you might not want to use planed timber twice.
18mm plywood bends between the 4x2s backing it up and where the ply is nailed to the 4x2s you will see the nail heads in the concrete.
The cheapest planed timber might be floor boards. But floor boards need to be supported underneath every 400mm. If you have 4x2s vertically behind floor boards then you need rods every 400mm as well.
If it were for me, I think I would use scaffold board timber. 38mm thick only needs the rods and strongback timbers every metre.
You could buy scaffold boards then get them planed through a thicknesser.
Another advantage of a thicker board, compared to 18mm ply, is that you can fix through the brace into the board from the back. This makes striking the formwork much easier. It also means no marks in the concrete from screw heads.
Very few signs of electrics in all these bare concrete walls. I have another page about electrics.
I always use Turbo Coach Screws from Screwfix. M6 dia. 8mm hex head. They drive in and out easily with the right cordless tools and with a 70mm long screw it goes through the 47mm upright and 23mm into the 38mm thick scaffold board without leaving a mark the other side.
The joint between the scaffold board needs to be patched over with plywood.
But if all your joints were haphazard then the board above and below a joint would be strong enough to stop the wall length spreading without a patch. But the board ends might bend in under the weight of concrete. That might be a reason for using 6x2s instead.
You should experiment with a sample wall of sufficient height to have the same concrete pressure your actual walls will endure.
I took this photo years ago. The carpenters that formed this wall with plywood did not clean the bottom first so water leaked through sand under the concrete and the rebates were supposed to line up and be continuous, but they aren't continuous and one section of wall is stepped back from the other.
This is a pub beside the Thames in Fulham. I doubt it was originally intended that this soffit would be on view. The carpenters would have noticed one sheet of ply caught on another, but they couldn't be bothered to put it right.