Tuesday, 5 February 2013
Post And Beam Strawbale Extension Part 6
Well it has been about 4 years of work but finally I have finished something!
The outside of the straw bale extension is now finished, rendered with clay and then lime and lime washed.
When I say finished I mean not temporary while we live with it! The whole of the rest of the house was never finished because, one, we are living in it which often leaves no drying time for finishes and two, no money!!
The plan is now to finish the inside of the extension and then move in to it lock stock and barrel and empty the rooms we now live in so I can finish the rest of the house.
So my experience of lime seems to run contrary to a lot of what I have read. When I first started to use lime as a render, a lime wash and a mortar I used plain old cheap builders lime (hydrated lime) it was all I could get. I used it for mortar for the limestone stem wall for the cob bathroom, render and lime wash, and found no problem at all with it which is completely contrary to what I read, (mainly from sites selling extremely expensive hydraulic lime).
In my experience a few bags of building lime dumped into a container of water and left a few weeks makes perfectly usable lime putty which can then be used for mortar, render or lime wash.
For the extension I used traditional slaked lime which I found in a local farm shop, this is the fired limestone that one has to put into water to activate. It is quite an amazing process, dump the bag of stones into a large container full of water, wait thirty minutes and one has a boiling mass of dangerous (there is a reason lime is used to destroy the flesh of diseased dead animals!!) white bubbling spitting lime putty. Wear protective clothing, glasses and stand back!!
In a way I was quite disappointed that this lime was no different to the bagged lime available in any builder’s merchant but it is much more fun!
Traditionally one is meant to add horse hair to a mix of lime render to stop it cracking when it dries, we don’t have any horses but though we do have dogs I thought they would prefer not to be shaved so I used sawdust as the fibre content.
The mix was 12 shovelfuls of sand to 2 shovelfuls of lime putty and 4 handfuls of sawdust and this gave a mix that has not produced one crack!
The lime wash was put on with 5 thin coats, it could do with another couple of coats but those I will do when I do the whole house.
Pressure and time are the secrets of lime. Limestone is created by a downward pressure on trillions of shells, and for some reason that is where lime as building material is best, where there is a downward pressure such as mortar. Lime render needs pressure to push it up against whatever one is rendering and lime wash needs to be pushed into the mortar with a suitable brush (not a roller). And where as cement takes days to harden, think months with lime, time and pressure!
Next job is turn this below into a beautiful living space.