We are prepping to build a earthbag house in the mountainous region of VA (we were able to find an architect willing to work with us in order for us to get approved by the permitting board. Woo!) and I want to start slaking lime as soon as the permits go through so it's nice and fat by the time we actually need to use it to make the plaster finish. But the only source I can find in the US that sells quicklime (not hydrated or hydraulic, just regular ol' CaO ) doesn't sell it in powdered form. The smallest I can buy it is granular fines. Will granular fines still slake okay, or will this lead to a wonky, gritty lime putty? We could get hydrated lime in powder form a little easier, but we'd prefer to work with slaked quicklime as that's the most eco-friendly option (while hydrated lime is just made with water, it's made in a special industrial hydrator, and we would much prefer to just let it sit in sealed recycled 50-gal drums than buy a product that needs any more processing than necessary) So will this granular fine quicklime work? If not, can anyone help us with finding a powdered quicklime supplier? Or are we stuck with hydrated lime?
I haven't worked with quicklime, only hydrated, but I suspect that it may take longer to slake down to a smooth consistency, but once fully hydrated it would... be fully hydrated, and therefore smooth, especially once mixed with sand for use.
Maria Arboleda wrote:Why don’t you use hard wood ash instead?
I like working with wood ash in lime, the problems I've had is that for larger projects it's hard to get ahold of enough ash that's consistent enough quality. For small projects it's no big deal but getting ahold of literal tons of ash is difficult. I really like the wood ash from pellet stoves because it's so consistent and fine, the stuff from conventional wood fire places has a lot more "chunks" in it and requires processing to make smooth enough for plaster use. Maybe you live somewhere else or have some kind of hookup that I don't.
You may be interested in following the process through from beginning to end – although you may not want to burn your own limestone, you may want to slake quicklime.
If you are able to do it, you will save money, but it can be dangerous, and you may not be too popular with the neighbours, as it gives off lots of fumes.
It’s difficult for the public to buy quicklime, as it’s dangerous.
If you are thinking of slaking your own lime, read about the Health and safety aspects of it.
Quicklime is more dangerous than putty, as it is in powder form which can blow around, and putty is mostly water, which dilutes and turns the thirsty quicklime to calcium hydroxide. Mortar and plaster is less hazardous still, but we still advise using goggles as it can burn if it gets into your eye.
Do it in a very well-ventilated place, preferably outdoors.
If you do buy quicklime, it’s probably better to ask for powder and not small lumps. We have found small unburnt limestone pebbles in the middle of lumps when we’ve come to slake them, and have had to pick them out of mortars and plasters later.
Don’t store quicklime – slake and store lime putty. Lime putty gets better with age, but quicklime could begin to slake itself from moisture in the air (and then it could actually start to take CO2 from the air and start to become calcium carbonate again!), and become useless.
To slake it In a large metal container, (an old bath is ideal – nothing plastic though, as the heat generated by the reaction will melt it)
make sure the bath is stable (by wedging it with bricks etc.) and of course that the plug is in or the hole filled,
add one part quicklime to three parts water.
Always add quicklime to water, and NEVER water to quicklime, as it will spit, and can be very dangerous.
There will be a violent chemical reaction with heat given off. You can test a small amount in a metal bucket first. If the reaction is sluggish, you can use hot water, although we’ve never found any quicklime to react sluggishly – quite the opposite in fact.
Temperatures over 100°C are achieved – water boils, lots of steam given off – and there will be some quicklime in the steam, so best not breathe it.
Wear a face mask and goggles. If the reaction is sluggish, or the mix is too wet, it probably needs more quicklime
Rake continuously until all lumps are removed. Rake backwards and forwards with an old rake. When the bubbling stops and there are no more lumps, cover with an old board with bricks on top, and go back to it to rake it again after an hour, and then again an hour after that.
Then cool, shovel the putty into plastic buckets (with lids to stop surface water evaporating). Lime putty generates water that rises to the top when it cools. Make sure this layer of water is retained in the bucket before you put the lid on. If there is no film of water, add some.
Leave the putty for at least 3 months – it will generate its own lime water on the surface. Putty must not be exposed to air.
The longer you leave the putty, the better it will be, and it will ensure that absolutely all the quicklime is slaked.
Store in a frost-free place.
Lime putty will store forever, as long as there is a layer of water at the top, with a lid.
If you have the facilities to slake your own, it will be cheaper, because putty is mostly water.
There is more information on the site detailing the economics of the activity.
John Daley Bendigo, Australia
The Enemy of progress is the hope of a perfect plan