Tagged: straw bale building

A (psychological) door

DSC_0008We 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.

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More flooring

DSC_0696I 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.

 

More refinements

I have abandoned putting the first coat on with a trowel, relying instead on putting it on by hand and then really grinding it into the straw with the heel of the palm. This way you can put some real force behind it and actually feel when you have a really firm contact. I then trowel on a 10mm or so layer to build the coat up a bit – as well as mashing in some long-straw to dub-out the uneven places. We will now wait until this layer dries before making a decision on whether to use a mesh in the final coat.

I have also worked out a way to get good chopped straw for fibre. This involves chain-sawing the face of a bale and then putting the resultant chopped straw into a dustbin and then using a stimmer to shred it further. I got this idea from this video (https://www.youtube.com/watch?v=lEfmPKnzvZ0). I am also using a slip coat mix about the same consistency as the one in this video  Рwhich is more liquid than the type Barbara Jones uses in her plastering course video.

I have also slightly adjusted the mix – moving from a 1:3 clay to sand mix to one which has a little more clay in it. It came down to feeling the final mix. There is a fine line between a mix which is grainier than it is sticky, to one which is stickier than it is grainy. The sticky mix is what I am after – and there is not much in it in terms of how much clay to add. The technique is to start with about 3/4 bucket of water plus one bag of clay plus a handful of chopped straw, mix – then add a bucket of sand and mix again, then add two more buckets with a handful of straw – mixing between each one.

 

Fitting the first window

20161109_145723I have found an online supplier (TA Windows) who can provide windows to almost any customised specification. With a straw build you are likely to need customised windows because the basic measurement unit is the width and depth of a straw bale and this tends to rule out designing to use standard window sizes.

Rather than take the risk of ordering all the windows at once – and then finding there was some problem with measurement or fitting, I got one as a trial – which I have now fitted. The key lesson was the importance of undersizing rather than oversizing. Despite knocking-off the recommended 10mm from what I thought was my gap in the sub frame, the fact that the frame was not absolutely square meant that the window didn’t quite fit. This wasn’t a problem, it just meant that I had to fiddle around shaving some wood off the subframe. However, I wouldn’t want to have to do this with every window.

Having to fill a gap between the window and the sub-frame is not a problem thanks to the wonders of expanding foam, in fact having a bigger gap is slightly better than having a very small gap in terms of sealing it with foam. I know expanding foam is not a natural product and I am sure Barbara Jones would not approve, but I figured that it doesn’t intefere with the key natural characteristics of the building – which is breathability and flexibility. When it comes to getting a decent airtight seal in tricky places where straw doesn’t really work, either because you can’t wedge it in or you don’t have sufficient depth, you can’t really beat expanding foam.

The only drawback is that the cans sold in most builders merchants are effectively single use, because the nozzle pipe can’t be cleaned. However, it is possible to get a gun which has detachable / re-sealable cannisters which also comes with a solvent cannister that can be attached and used to flush through the gun nozzle. This makes it possible to do small jobs.

Following this trial window, I have gone ahead and ordered all of the windows and while waiting for delivery have got on with some small, fiddly but necessary jobs such as fitting guttering and putting a galvanised wire mesh around the bottom of the foundation beam to stop rodents getting under the suspended floor. This is a condition of building regs, but I don’t know if this will make a difference, since my experience shows that a determined rat can get around almost anything, including building regs.

Second (and final) coat

This past week or so I have been getting on with the second coat, which I also intend to be the finish coat. The mix I have been using is firmer than that which went through the gun for the first coat, but still relatively sloppy – given the that it is serving also as a ‘float coat’ albeit I am not looking to get an especially smooth finish. The depth is probably a minimum of 10mm, although it gets much thicker in places given the uneveness of the straw and holes or depressions in the first coat.

Most important learning is the degree to which the first coat will rapidly draw the moisture out of the second coat, making it quite difficult to work – hence the need to ensure that you give the first coat a good drink before putting the second on. It is amazing how much moisture the first coat will suck-up.

I am not using the gun, just loading the hawk up with a good load of render and then pushing this on and up using a trowel. I then quickly work this to get a reasonably smooth and even coating and finish off by misting it and going over the surface with a sponge trowel. This helps cover the trowel marks and produces a relatively even but rough textured finish – which has about the right amount of ‘hand-madeness’ I am looking for.

This doesn’t require a huge amount of skill and can be done quite quickly – not quite as fast as I could go with the gun, but not far off. I reckon I can get through about 7 square metres per day. This is a relief, since I was worried that my attempt at a finish coat would either require a huge amount of time and/or end up looking like a bodge-job. This isn’t to say that plastering could be considered easy, but it is not too hard if you are happy with a what might be called a rustic finish.

I know that time is ticking on and I am now well out of what traditional lime people would consider to be the rendering season. This might be the case if I was using sand, but with the chalk and fibre mix I am confident that I have something that will be resistant to all but the hardest of frosts and that if it looks like a cold snap is on the way, putting hessian up should provide enough protection. There has certainly been no evidence of any sort of cracking developing on either the first or second coats thus far.

The only other job this week has been to order the window cills, since as you can see from the pictures, I haven’t yet finished-off the area around the windows and am waiting to get the cills in before doing this. I have set the windows quite deeply, which means the cills need to be 220mm deep – i.e. much wider than any standard widths, so I have had to order the wood (oak) from a local sawmill. I am going to use just a flat plank and set it into the frame with a downward angle, resting on top of the straw/render rather than going to the expense of having a custom-made cill, with flat base and angled top since I figured this is only necessary if you are fitting your cill onto a flat surface such a a course of bricks.

 

 

Experimenting with render

A few days ago, Martin Browne from Warmcote, came round to try out his Limecote mix and also see how this worked using a render gun.

All-in-all it was pretty successful. My main concern was to see how easy it was to get an initial coat on using a spray and also how much a coat of render would expose the imperfections in the wall, in terms of gaps between bales and inaccurate positioning (and thus how much dubbing-out work might be required).

Getting a coat on was straightforward. The beneft of Limecote (which uses lime hydrate, chalk and a heavy dose of artificial fibres) is that it mixes with a conventional hand-held mixer and also can go through a pretty lightweight (thus cheap) gun, powered by a small (thus cheap) compressor. We were actually using a spray paint gun, not even a proper render gun, with a 2hp compressor. As the video shows, it went on pretty easily and penetrated well into the straw.

We then made up a mix with quite a lot of straw in it, as a dubbing mix. Again, we were able to do this using the hand-held mixer. This didn’t fix well to ‘naked’straw, but was fine when applied on top of a sprayed layer. By pressing this mix onto the walls it was relatively easy to flatten-out imperfections and get to a pretty good finish.

One thing that was very noticable is that the cut and folded ends of the straw take the render in different ways. The cut ends present a very firm surface, albeit with lots of vertical ridges as a result of the layering / flaking of the straw as it was packed into the baler. The folded ends didn’t have this ridging (which needs to be filled-out with render) but were much softer and thus had a tendency to form a hollow. Since we had alternate layers of cut and folded ends this had the potential to create a slightly wavy surface, which required the long-straw mix to flatten-out the hollows on the bales with folded sides. Perhaps we would have been better having all our bales presenting the same way (say cut ends on the outside and folded on the inside) – but we varied the layers following advice from someone who had found that the folded sides were slightly thicker and thus made the wall start to bow inwards or outwards after a few layers.

After Martin had gone, I prepared a mix that was even more straw-heavy – i.e. pretty much just coated straw, rather than render with straw within it. This seemed to work well for dubbing out big holes and depressions.

Martin reckoned that the best technique would be to spray an area, gently even this out with a flexible edged float and then press-on the long-straw mix to get to a desired straightness of surface (accepting that I am not looking for a perfect, flat finish). This layer would probably vary between 10 – 30mm. This should then be ready for a finish coat of about 10mm.

The test layers have now been up a couple of days and seem to have got a good fix and be setting nicely. The one slight drawback was that the straw started to leach its colour into the render, especially with the staw mixes. I guess this is less likely to happen when using a sand-based render which is already more straw-like in colour and also where the sand is much less moisture permeable than chalk. If this comes through the final coat I will have to put a straw-coloured limewash, or sufficiently pigmented to drown-out the straw leaching.

20160516_141919

On the right: long-straw dubing mix (plus colour leaching), on the bottom left: finish after spraying and levelling , centre left:sprayed coat plus second (finish) layer

 

 

Preparing for straw

20160225_164142The last week or so has been spent on the rather tedious ask of fitting all the noggins for the hazel stubs and fixing all the window and door posts. These posts requre careful work in that they need to be securely fixed into the baseplate, be absolutely vertical and also slotted through (but not permanently fixed into) the roof plate so that the plate can move downwards when compressed. Other fiddly jobs were finding ratchet straps for compression and also tracking down and ordering 19mm composite polyester strapping plus a strapping tensioner and buckles. I had no idea there were so many forms of strapping and strapping kits. In the end I used JustStrapIt.

 

 

More excitingly, the farmer from up the road, Owen Wilson, delivered the first batch of 120 bales – so we are now set-up to start wall raising this weekend.20160229_111356