[Cob] Making lime wash stick

[jane at kirstinelund.dk]

There was a question some days ago about additives to lime wash or other
tips on how to avoid that it comes off. I wrote an answer, but my mail
program ate it and I haven't had time to re-write it before now. Here are
my tips:

1: Put the lime wash on in thin layers. Mixtures of between 1:5 and 1:10
(lime and water) are generally recommended, and I think 1:5 is a little
too thick. You will have to put on several layers (usually 4-6), but the
result will be better.

2: Use lime water. When you mix lime and water and leave it to stand for
some time, the lime will fall to the bottom, and the water you have on top
of that is lime water. Somebody told me that you get the best lime wash if
you prepare the walls by giving them one layer of lime water, but now I
just read that you should use lime water as the LAST layer, as it fixates
the lime wash. I don't knoow if lime water as the first layer is just a
misunderstanding of the other tip. Anyway, it probably doesn't hurt...

3: Even though pure lime wash is supposed to stick well and not come off
if it is put on properly, there is an old reciepe on casein lime wash,
which is supposed to give a harder surface. Here you mix in casein
containing milk products. You can use buttermilk (which is quite common in
Denmark where I live but I have an idea that most other countries
considers it undrinkable) or curd cheese, and probably some other milk
products, but not all.

The homepage where I found the reciepe is out of order, but I think it was
something like 1 lime, 1 buttermilk/curd cheese and 6 water. Mix
everything and leave it for a day or so before you use it, as the lime and
the casin needs time to react. If you mix too much you can leave it for at
least some weeks before it spoils.

As I am not sure of the reciepe it is probably safest to use less
buttermilk, for if you use too much the paint surface will crack. Too
little will just have less effects. And it's probably safe to use a little
more water, also.

We used buttermilk-limepaint on some inner brick walls and it worked fine.
It is supposed to be good for outside walls also.

These tips are for hydrated lime and NOT for quicklime which I had never
heard of before - it sounds awfull. Denmark is more or less bould on lime
rock, and though people have used it less and less for the last few
decades (and have you ever seen what happens if you try to plastic paint a
lime washed wall?) it is very easy to some by.

4: By the way hydrated lime comes in many qualities. We distinguish
between ordinary slaked lime and clamp/pit (???) lime (the danish word is
"kulekalk") which has been stored wet for a long time, and which will give
a harder and more permanent surface. The first (and cheapest) kind might
be good enough for inner walls but on outside walls it it best to use
"kulekalk"

Jane