We have just fitted the door. This was actually a very simple task (using the same company as supplied the windows), however it represented an important psychological milestone. Whilst your door is a sheet of OSB you don’t really have a house, you have a building site. It also means that we have a proper air-seal so it makes sense to light-up the pellet boiler – an important step forward given the sudden plunge into autumn.
One of the many finishing-off jobs is putting on a rain skirt at the base of the building. This has two functions: to protect the base plate and throw any rain that runs down the building away from the foundations and also to protect the car tyres from direct sunlight, which can cause them to degrade.
Before rendering I had screwed a 2×2 timber through the woodfibre and into the timber of the base plate. This acted initially as a render stop, although the sticky nature of the Limecote mean this wasn’t really necessary. What I have now done is screw a piece of standard black stained weatherboad at an angle into this timber and nailed onto this a piece of 90 degree angled plastic beading. This beading can act as a new render stop for a a strip of render that overlaps the top of the weatherboard (see pictures).
I am pleased with the result. It finishes-off the base of the wall and gives the the whole house a slighty suspended feel.
Elsewhere, I have been finishing off the flooring and been back on the tyres and gravel again, but this time for the less critical job of providing a foundation for decking. I will use the scaffold boards so that the same material that is the interior flooring also then runs-out as ‘exterior flooring’ albeit with a small gap between the planks to allow rain to run-off as well as having set the decking on joists that are on a 1% angle to further encourage run-off.
I am now putting in the finished flooring on top of the chipboard sheets that sit on top of the joists. I have decided to go for scaffold planks. The problem with most conventional flooring products is that they all look too perfect (as well as being pretty expensive if you want solid wood as distinct from a laminate). For a project such as ours you need to have a floor that looks suitably rustic – and scaffold boards do just that.
Scaffolding Direct sells new, unbanded boards in various lengths, which work out at a cost at around £14 per square metre. This will give you a chunky 38mm, 23cm wide, board. The boards will obviously need to be sanded and finished, but the look is so much more solid and attractive. Interestingly, the price of new boards is about the same as recycled ones and since both would need to be sanded and the used ones are more likely to be damaged, as well as having bands on the end that would need to be removed, buying new seemed a better option.
I am nailing them down, rather than screwing them, because I think boards like this need to have visible nails to look suitably authentic. I would like to have used cut nails, but this won’t grip into the chipboard, so I am using good old ringshank nails. I got boards in lengths of 2.4m so as to get a good number of joins, since I think this also is a better look. I expect to get a little shrinkage over time, but this shouldn’t be a problem because big boards like this look better (more authentic if I may say that again) with slight gaps between them.
It has been a long time since the last post – mostly because we have been doing ‘non-straw’ jobs, such as installing bathrooms and kitchens and painting which are not especially interesting or noteworthy tasks. I have been meaning to write a review post covering my conclusions from clay plastering, but haven’t got round to it yet. However, last week I got back onto a straw specific job, namely finishing off the exterior render around the windows.
I had left the window area without a finish coat because I needed to get the windows themselves in before doing this and I wasn’t able to do that job before the winter lime rendering window closed. As luck would have it I received a surprise visit from Arthur Phillip, the lime render man, who happened to be in the area. Arthur is probably the country’s foremost expert on rendering straw bale houses and he introduced me to PVC window frameseal beads. These are basically a strip of white PVC channel with a sticky back to it that you can put around the wooden frame edge of the windows allowing you to render up to and into the channel – thus giving you a stable and watertight edge to your render. They also have on the a tear-off sticky plastic strip which you can use to attach polythene sheeting to in order to protect the windows themselves from render spalshed – important if you would be using a gun to apply the render.
I couldn’t actually source these in sufficiently small quantities, so I made my own by buying standard PVC channeling and runing a bead of silicone up the back of them to stick these to the frame while also creating a weathertight seal. I then mixed up a batch of lime and straw to create the shaping into the window frame and finished-off with a coat of lime that then ran into / up to the window edge fo the PVC channel. This seems to work fine.
I am now close to finishing the second coat – having been at it for nearly a month. Fortunately I have been able to borrow a cement mixer, which makes the mixing much easier and has probably come just in time to preserve the life of my hand-held electric mixer which has been showing the strain.
The basic procedure that seems to work is as follows.
First put a dry mix of one bag (15kg) of clay plus ten shovels of plastering sand into the mixer together with a couple of good handfuls of concrete screeding fibre. I have opted to use this instead of creating lots of chopped straw, simply because it is easier (and seems to work).
Then leave this to turn-over for a good 15 minutes to get it well mixed and also to tease-out the fibres (they come out of the bag as short strands, but are in fact pieces of mesh and by stretching the out you greatly increase their volume/area).
Then add about half a bucket of water to get a consistency of mix that slumps well in the mixer, but doesn’t stick to the sides. It is also important to ensure it is wet enough to avoid turning into small pellets because if this happens it can be hard to get these to blend-out. Leave this for a good 10 or 15 minutes to get smooth and well mixed. Then add the remaining water to produce a consistency of mix that is close to that of butter icing. This will tend to stick to the sides – so may need a little prompting with a spade to ensure the water works its way through. While the clay is mixing give the wall a good soaking. It is astonishing how much water a dry clay wall can suck-up and if you don’t take the edge of this it will pull all the moisture out of your final coat. I put the mister on the hose and wet the wall down just to the point where water is about to start running down. Then I leave it for a minute and do it again and perhaps even give it a final mist just before starting to plaster
I then apply the clay in quite a rough-and ready way using a plastic trowel and once I have done a decent-sized area I use a sponge trowel to smooth things out. The advantage of a sponge trowel is that it can move the top 2mm or so around without dragging the whole coat.
Once the coat has firmed-up a bit I then rub it down with a regular sponge. The use of the two types of sponges can pull some of the fibres out of the mix a little, leaving a slghtly ‘hairy’ finish, but these can either be brushed-off when the coat is nearly dry or I am hoping they can be encouraged to ‘lay down’ when the wall is painted. Even if some still poke-out I don’t mind the fact that the fibres are visible because, to come-over a little bit Kevin, it “tells the story of the material” (we can see the horse hairs in the 16th century plaster on the inside of our house for example). It gives a slightly rough finish, but I think this looks fine. It would be possible to give a smoother finish if you worked the surface with a plastic or wooden trowel, bit this would take ages and probably look a bit odd, given the natural irregularity of the walls. You could try and use a flexible rubber-edged trowel, but this would probably only work if you were able to get a much flatter finish, which would involve a great deal more clay.
Results from the walls which have dried out are encouraging – very little cracking, such that it will be easy to hack-out the one of two that have developed and patch them over, possibly with a strip of hessian of fibre-glass mesh.
It is, however, very slow-going, especially doing the detailing around the windows. Renderng and plastering will be by far the two biggest jobs involved in the build.
I am now getting round to the fiddly detail bits. One of these is fitting notched bales between the top the main interior wall and the roof (the bales have to be notched to allow for a purlin) and also putting bales in place above the doorways. It was good to return, one last time to ‘straw work’ athough cutting the notch with a chainsaw meant becoming swamped in loose straw. It also reinforced that by far and away the best tool for cutting or shaping straw is an electric chainsaw (not a petrol one because the straw gets in the air intake and it overheats).
I have also been finishing off the clay around the windows and door frames – using a ‘cobby’ mixture of straw and clay. I want to plaster right up to the window frames, rather than put decorative wooden frames and window ledges in place. I think this sets-off the window frames to best effect, but it does mean plastering over the window sub-frames as well as sticking clay ‘upside down’ to the sub-frame above the windows. To do this I covered the wood in a flour, water and clay paste to give it maximum adhesion. This appears to have worked – although for the final coat I will also stretch hessian or fibre-glass mesh around curve, both to stop cracks developing over the join and also to hold the upside down plaster in place should it feel like falling-off. The job feels a little like being a housemartin, sticking clay and straw to the underside of eaves – and the resilience of their nests gives you some confidence that the clay, with added flour paste, will be sticky enough.
We have now had a chance to see what happens as the base coat dries-out. There are some cracks developing – but not many. I have probed any large crack to see if this indicates any fundamental weakness in the straw or adhesion beneath, and for those where there is significant softness I have pushed my fingers in more strongly and forced the clay back into the straw / gap – and then filled this out with more base coat.
I have also changed the approach to the first coat – moving away from a very liquid pure clay slip, to a mix that is 1:2 clay to plastering sand (no fibre). This gets over the probem of pebbles blocking up the gun because the sand is finer and better sieved (albeit more expensive). I get the mix to the point where it is a cross-over between liquid to solid but where if you dip a piece of straw into it you still get a good amount clinging to it. I have then sprayed this on just to the point where you stop just covering each bit of straw and start getting ‘fill’ between the bits. This we will then leave to dry-out a bit before putting the 1:3 base coat (plus fibre) on.
I have also noticed there is a marked difference between the bales whch present a cut face and than those with a folded straw face. The cut face is already pretty rigid and stable and therefore doesn’t require much to cover it, whereas the folded face is more wispy and requires more material to really get into the straw and stabilise it.