Problems with coloured limewash

[Ruth]

I have recently been painting the interior surface of an exterior wall with limewash. Firstly with base coats of plain white limewash, then with several coats of coloured limewash. The limewash was made using lime putty (a 1:2 mix) and the coloured limewash contained a small amount of strong red pigment (soaked in warm water for 24 hours before it was added to the limewash). All coats of limewash were allowed to dry for 24hours before subsequent coats were applied. The wall was misted before each application.
I have encountered two problems:
a) Some areas of the wall did not take up the coloured pigment - I could not work the limewash into the surface it just rolled off. These areas are still pale.
b) Several days after I last applied a coat of limewash areas of dark red mottling appeared near the window. It looks almost as though pigment has somehow accummulated here!
Can anyone give me any clues about what is happening and how to rectify the situation.
We moved to our traditional stone'built property in west Wales two years ago and are enjoying learning about and using lime but need some help with this!
Many thanks.

 

[Schoolmarm]

What is under your limewash?

 

[Gervase]

It looks like overpolished plaster is the problem here. It often happens with uneven stone walls - the thickness of the plaster varies hugely, and it's easy to overpolish some of the thinner areas, resulting in patches of very hard, dense plaster which is made up of lime and 'fines' from the aggregate. They tend to shrug off the initial coats of limewash, and then darken and become slightly shiny.
Thorough mixing of the limewash is also vital if you want an even finish (and with a pigmented limewash it's important to realise that you can never get a totally uniform finish). A basket whisk on an electric drill is ideal. If you have consistent problems with the limewash not sticking, some casein powder or linseed oil whisked in well will help - an egg-cup's worth to a three-gallon bucket.

 

[Ruth]

Thank you for the question, and for your reply Gervase.
The wall I have been limewashing was lime plastered last autumn.
We moved to the traditional stone-built (slate) property 2 years ago and found this wall was very damp. The exterior (east facing pine end wall) had been cement rendered and the render was cracking. The interior surface of the wall had also been covered in cement, the lower section painted with pitch and the whole lot covered with polystyrene-backed plasterboard.
We took the plasterboard and cement off the interior surface a year or so ago, and also removed concrete blocks used to fill in a doorway and re-built in stone. Then in May last year we had the cement render removed from the outside and a thin coating of limeplaster applied followed by 7 coats of hot limewash. In the autumn the interior surface of the wall was platered with lime. Some cracking appeared after a few days and the guy who did the job for us came back - I think he remedied the situation by applying another thin layer of lime plaster, I also remember him working over the surface with a glove to deal with some issue(?) He didn't use a metal float though.
When I came to limewash the wall there was some very fine cracking again - one of the reasons I used 3 coats of white base was that I wanted to fill the small cracks.