Question about distemper
Does a new lime plastered wall need to be coated with distemper to allow it to breath or do modern emulsions do the same ? is distemper applied in the same way as emulsion ?
Just to clarify, and avoid the misunderstandings:
Distemper bound with casein is based on chalk with a casein binder that makes the coating non-chalking and non reversible and not necessarily super breathable.
Soft distemper is based on chalk. It is chalking and reversible (ie can be washed off) is very porous, and is suitable for ornamental decoration.
Lime wash is based on lime. It is also chalking and porous and should not go on top of other coatings. It is suitable for interior and exterior lime plaster walls.
(Patrick Baty is the leading authority to grill on the technical nuances and differences)
Lime wash on interior lime plaster walls
The traditional finish on lime-based plaster is lime wash.
lime putty and water to a thin single cream consistency (I seem to remember 40kg lime made around 150lts lime wash), pigment if wanted, about 250ml boiled linseed oil (stops it rubbing off on your hand when dry).
I used a big 180lt barrel and a plaster mixer on the end of a drill, but then I was painting everything inside and out and wanted colour consistency.
Apply about 3 coats.
You find that it doesn’t look like you’ve done anything but wet the wall to start with. Then it dries and starts to go opaque. Wait till it is dry before re-coating.
If you are near Bristol then Chards have everything you need – H J Chard & Sons, 1 Cole Road, Bristol, BS2 0UG. 0117 977 7681
How to apply limewash
Check out the video. The basic premise is to damp the wall first, apply a watery coat with a block brush, wait 20 minutes and then scrub the surface with a dry brush to even out the coat as well as possible. Leave 3-4 days and repeat.
Lime wash on exterior lime render
On ProjectBook, this article on exterior lime render explains the whole plastering process and the requirements for curing etc. Their recommended painting process is 4 coats of limewash with some added boiled linseed oil.
The silicate masonry paint they refer to in the article, I know of KEIM paints, which in simple terms combine with the substrate rather than lay as a coat on top of it.
Emulsion paint on lime plaster
You definitely want to avoid modern vinyl emulsion on lime plaster because lime plaster is breathable and vinyl emulsion would seal it and negate the breathability benefits of lime plaster.
Technically, cheapo contractors emulsion, Supermatt and the like are breathable, and are a suitable modern choice as a sealer / wash coat and finish on lime plaster (as well as on modern gypsum plaster surfaces).
So would I use Supermatt emulsion on new lime plaster? On exterior surfaces, definitely not, for reasons of durability. On interior work? I think some heritage-conscious plasterers and restoration folks would probably shoot me if they saw me use supermatt, but would they be right to be so disdainful? From a technical point of view, no, because it works. But if purists wanted the new lime plaster to be painted with lime wash, as in days of yore, then any emulsion would prevent the walls from ever being over-painted with lime-wash.
I have learnt from Patrick Baty, that not all modern paints are inappropriate in a traditional property, and it is good to realise that many traditional finishes also produced their own issues. Maintaining tradition is a good aim, but you have to realise that not everything old is good – tinkering with paint recipes didn’t start with the discovery of the oil industry. Craftsmen of olde always modified commonly used materials, trying to make them perform “better”, but as you can see from the introduction, overcoming some deficiencies in distemper, like chalking, result in frankenstein scrubbable impermeable hybrids that can create many vexing issues further down the road.
If you have any questions, post a question on our heritage decorating forum and we will do our best to help. TP decorators like Matt Evans of Welsh Heritage Decorating work with these products regularly.
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