With the photos below I think I've managed to get this blog back in sync with reality on site. The top two coats of lime render have gone on and gone-off (dried and cured sufficiently to be safe - touch wood - from the winter weather) and are now protecting the bales properly from the rain. The final coat was made with recycled glass aggregate (crushed and tumbled bottles), then scrubbed-up to strip the lime off the big bits of glass. From a distance it has an off-white appearance, but as you approach an increasing amount of colour and just enough sparkle is visible. We love it. Much time has been spent staring at the walls with huge grins on our faces. I have an obsessive amount of render-finish photos, taken in different lights and different stages of dryness to try and best capture the colour and sparkle. It's really hard trying to resist showing them all to anyone who asks about the bungalow. I've been selective below, in the understanding that one person's beautiful render album is another's endless close-up photos of a bit of wall.
The lime needed looking-after during it's initial setting: to cure/carbonate properly it needs moisture and air. If it dries out before curing it has to be sprayed with water to keep it moist, and if the sun is directly on it and trying it too fast it needs covering. Only the south wall of the extension ever caught enough sun to need protecting, and that was easily covered in hessian (which shades it whilst still allowing air and water through). The sun was short-lived in any case - most of the time the weather has been quite mild and damp which is probably ideal lime-curing weather. Each layer of render did still dry out quite fast though (it's quite a windy spot up the hill) and needed regular damping down. It felt particularly perverse having built large roof-overhangs to protect the walls from direct rain to then be spraying the walls directly with a hose, sometimes while it was actually raining.
It's very satisfying to see the colour change in the render with each spray of water - initially it's all a bit creamy in colour, then lighter when dry, then back to cream after spraying. Once the surface at least has cured it goes a cleaner white colour, which starts to hold even when wet again.
The other danger to fresh render is frost, but thankfully the mild weather held long enough for the lime to go off enough to be safe. If it had frosted earlier we would have had to wrap all the walls in hessian to protect them.
The rendering was done by Lime Repair who have done a fantastic job, giving our home nice crisp lines and lovely gentle curves, and helped get me started with the scrubbing.
Tomorrow a huge delivery of thirty pallets and tonne-bags arrives, containing all the recycled foamed-glass aggregate for the floor insulation build up, and the the lime and other recycled aggregate for the limecrete slab that'll form the new floor base (from Ty Mawr). Fitting it all on site around the tree at the front will be awkward but I think it'll just squeeze in within reach of the lorry's crane. Also on that delivery will be wood-fibre insulation boards which will be used to insulate the remaining area of gable wall above the bale wrap, that corresponds to the vaulted ceiling indoors. I need to get those up quickly so that I can finally fit the timber cladding to the top half of the gable and get that end watertight.
The first coat of render revealed a dodgy bit of bale-dressing on the front corner (annoyingly I'd seen it when trimming the straw and had meant to deal with it but forgot). The render made the bulge in the middle of the corner more obvious - almost the first thing Sam the Plaster noticed on return to site - so I chipped off the render, pulled out a load of straw and retied the bale so that the corner could be straight.
Second coat of lime render (Float coat) going on over the scratch coat.
Sam the Plaster using a Straight Edge to put a straight edge on the wall
All trowelled on, but not yet floated up (rubbed-up with a plasterer's float once it's stiffened up)
After floating
For some reason I find this pleasing (it's actually horse hair to add to the render to strengthen it)
Woodlouse! They love lime. Somebody probably know why, but I don't.
Oak render stop sanded down, looking lovely after being limed (as well as lodging in the grain, the lime reacts with the tannin in the oak and darkens it)
The recycled glass aggregate (crushed and slightly tumbled bottles, supplied by Ty Mawr) arrives, causing much excitement with me and the plasterers. We kept grabbing handfuls and letting it run out through our fingers and laughing like pantomime villains with their hoard of jewels.
The big sack of jewels
Cream together the butter and sugar...
Sam the Plaster trowels on the glass/lime mix in the back porch, the only bit where it'll be flat (though we like it so much we now plan to use it inside in a few places where the light will catch it)
Julie Lime-Repair (boss) escaped the office to come and play with the glass
Back with the sprayer for the roughcast coat on the outside walls
As before the sprayer covered everything, with the crunch of the glass underfoot part of my mind kept thinking it had snowed. Here drip from the gutter has washed the lime/snow away to reveal the jewels within
It looked a bit toothpasty or softminty at this stage
Snowy wall
A small test, using the glass with clay plaster for the bathroom (also mixed with a little lime-putty to help it stick to the bricks and lighten the colour).
The walls emerge from the plastic for the first time in weeks, finally complete.
From a distance the render appear a bit mottled, off-white. As you get close it shows the glass and sparkles a bit.
To strip the thin surface layer of lime off the glass I scrubbed it down with diluted brick acid (not very eco - but very small quantity used) and a churn brush. Thanks to Sam for helping figure out the best system. Eventually the system settled down to: spray the wall with water (once the render has gone properly hard), brush on the dilute brick-cleaner, scrub, gently spray with more water, scrub some more, then thoroughly rinse the wall down.
The flat section in the back porch, scrubbed up with a sponge.
Conservatory base-level finally set to the correct height, with compacted scalpings, ready for loose-fill recycled foamed-glass insulation.
The lovely sparkly render. I'm so excited by this.
Light doing nice things through the living room rooflight.
The brush on the right has just been used to scrub down all the walls to reveal the glass. Before that it was more like the brush on the left.
Glassy roughcast lime, with newly-oiled oak render stop
Sunroom structure just had it's first coat of oil too (using Osmo UV protection oil, which will leave a fairly matt, satiny finish once it's soaked in and dried, and will allow the wood to breathe).
The main eaves beam still awaits its first coat. It was getting too cold and damp in the late afternoon to risk carrying on - a problem with trying to do outside finishes in late November. That and the fact it's dark just after 4pm. Still, very satisfying to have got this far.
I'm behind with updating this blog again. Enough changes have happened and photos amassed for at least two blog posts. First up: the initial coat of lime render went on a few weeks ago. This took three days, was sprayed on to drive the lime as deep as possible into the straw (for a good strong bond) and was overwhelming to watch, as the stack of bales suddenly became a building.
Here's a very short (and only slightly geeky) video of the lime being mixed and sprayed (in a fantastic roller-pan mixer which mixes it up and mushes out any lumps at the same time - one of these would be great for mixing clay plaster or even just clays in general for pottery use, but they're rare and expensive so I am unlikely to ever get one just for occasional use):
The render-gun is a pretty impressive bit of kit too, in combination with a large air-compressor. Three nozzles inject air through the base of a hopper full of lime, basically blasting any plaster out of its path forcing it out of the gun and onto everything within a four metre radius, but primarily onto the wall in front and the person holding the gun. A second person is needed - standing a little further back - whose goggles take a bit longer to get plastered, thus enabling them to direct the one with the gun (who rapidly loses sight as goggles become misted and spattered).
The render is a mix of lime-putty (pre-mixed, pre-aged, pure lime goop, roughly the consistency of soft cheese) and sand, plus some hair to add strength. Also added is a pozzolan - a natural additive that helps it set a bit faster. Unlike cement, lime doesn't have much of a chemical set to make it go hard rapidly; instead it cures slowly over time, as the lime putty (calcium hydroxide) reabsorbs carbon dioxide that was released during it's manufacture and returns chemically to calcium carbonate.
Lime putty is made by heating limestone/chalk to break the molecules and release the carbon from the calcium carbonate. This produces quicklime (calcium oxide) which is then slaked (soaked in water - a violent, dramatic, heat-producing reaction) to form the calcium hydroxide lime putty. More info on the lime-cycle can be found here, with handy diagram.
Lime boiling in a bucket after quicklime was mixed with water (slaked) - demo by the lovely Bee Rowan during the first strawbale I went on:
It is debatable whether lime has a lower embodied energy (the energy used to produce, process and transport the material) than cement, but it seems to be generally agreed that it does have a lower embodied carbon figure. The Greenspec website linked to above claims 20% less carbon emissions for production of lime compared to cement, due to the lower temperature lime is fired at. The Inventory of Carbon and Energy prepared by the University of Bath presents a more complex view:
Lime is often chosen as an environmentally friendly material. It was therefore surprising to learn that the embodied energy of lime was slightly higher than for cement. This was observed from the respectable sample size of 39 data records. Lime is fired in the kiln to a lower temperature than cement, which is often misconceived as proof for a lower embodied energy. The present authors suggest that yield, density, and time in the kiln are all vital parameters to total energy consumption and that firing temperature may not be used as a proxy for embodied energy. This is presented as a possibility for its higher embodied energy. It should be noted that embodied energy is, in itself, not evidence to discredit limes environmental credentials. Due to a more favourable fuel mix and slightly lower process related carbon dioxide emissions lime has a lower embodied carbon than cement. An additional benefit of using lime based mortar includes the increased ability for deconstruction, rather than demolition. The re-carbonation that occurs over the lifetimes of both cement and lime based mortars (when exposed to air) will reduce the embodied carbon impact of the materials. Its understood that this process is not undesirable for lime (unlike cement). Examination of lime's full carbon cycle, cradle-to-grave, is therefore necessary.
[Inventory of Carbon and Energy v.2, Prof. Geoff Hammond & Craig Jones, Sustainable Energy Research Team (SERT)
Department of Mechanical Engineering
University of Bath, UK, 2011]
Lime re-absorbs more carbon dioxide (CO2) than cement does as it cures, helping to make it a 'greener' material - all the CO2 released from the chalk or limestone is reabsorbed. So for lime the only real increase in atmospheric CO2 is any released by the fuel used to heat it.
Buildings built with lime are much more recyclable. At the end of a building's life lime mortar and render can be easily separated from other materials and recycled, also allowing for re-use of the other materials. Cement tends to stay too stuck to anything you put it on, making re-use of bricks, for example, very difficult.
Possibly the best reason for using lime render on strawbales is that it's "breathable" (vapour open), allowing any moisture that might find its way into the walls to escape. Moisture is drawn out through the lime and into the air outside. Bee Rowan (who ran most of the strawbale and clay plaster courses I did, and runs Strawbuild) always says lime render is like a Goretex jacket.
And finally, lime is much more flexible than cement, allowing the building to move and flex as it dries out, or the ground around it changes, without major cracking. Cement is very brittle and often stronger than the bricks it holds together, so if there is any movement it tends to cause large cracks, snapping the bricks.
The render work is being done by Lime Repair, who have a shiny new website here: www.limerepair.com
Now for some photos:
Adding last layer of scalpings (hardcore) to the extension floor. This brings it up to the correct level for the recycled foamed-glass gravel that will insulate and build-up the floor to the right place.
Common Toad, found during clean up for scalpings, relocated to the garden, near a good pile of stuff to hide under.
John who was very kindly helping me barrow the scalpings in was doubtful of my levelling technique (with a rake, by eye). We checked it and I felt quite smug. The area that he levelled later was much smoother though.
Momentous moment: the very first bit of render is sprayed on to the bales
Sam in a cloud of vaporised lime, demonstrating why a face mask is needed.
The render is blasted on then trowelled flat to compress it and push it further into the straw
Lovely lovely lime
The wonder-mixer. Apparently it's temperamental and awkward but I'm still very envious (especially as this one will run off domestic electric supply - many mixers like this need three-phase)
Lime putty/cream-cheese - the primary ingredient for the render
Surprise surprise, it belted down with rain throughout the morning of the first day of plastering, creating more mud everywhere to add to already very messy job
Lovely lovely lime again, mixed with sand and hair, ready to go on the walls
This coat is called the scratch-coat, for hopefully obvious reasons.
Pleasing detail by front door, one of Kuba's great design details (yet to be scratched)
Lime "fingers" where it's plastered up the reed matting, provides good grip for the render.
Gable wall gets it's first coat. Hessian scrim is used over any joins and every 'H' clip (the timber that clamps the bales onto the bungalow wall) to prevent cracking.
Checking something in the loft I discovered a bit of cavity-fill incident. Clearly they'd pumped a load up through the wall into the loft without realising. I'll spread it out at some point before installing the main insulation
In the loft
Dubbing out the walls (building out the depth where needed to create straight walls) using slate.
The un-trowelled spray finish - this part of the gable wall will be covered with cedar cladding.
