South Street gallery is an excellent supply. Pay special attention to the extra dry blocks . Make sure the walls are gooey. If you don't then the paint just sits in the surface and is easily knocked off. Use a broom to apply.
Rollers are no good.
Brushes are too slow. First coat ends up a mixture of mud and paint. Allow for at least 5 coats. If you want clean lintals and top plates, mask. Slightly more geletin seems to give a better result.