Mineral paints are matt and are best suited for painting on mineral surfaces, although they can be used on unplaned timber surfaces. The most common types are based on binders of lime, cement and waterglass, all of which are soluble in water.
The products are based on rich reserves. The environmental consequences of the production techniques can be acceptable. All products are however strongly alkaline and when damp have a corrosive effect on the skin.
Mineral paints are practically emission free in the indoor environment. They are also permeable to vapour transport and do not block the moisture-buffering properties of the materials underneath, and
18.3.1 Lime paint they are not electrostatically charged. Lime and cement paint if not well bound to the surface can flake off and cause respiratory irritation.
As waste the products are inert and will not lessen the painted product's potential for energy recycling.
In lime paint the binder is slaked lime. Curing is based on carbonizing slaked lime with carbonic acid in air, forming an even crystalline layer. The pure lime colours give matt, absorbent surfaces that are difficult to wash. The paint is porous to vapour and not elastic. It binds best to a fresh lime render but can also be used on cements, brick and rough timber, on the latter preferably with casein added to make the paint more elastic. In commercial products additions of styrene can be found.
It is important that lime paint is applied in thin layers. It can be used both inside and out, but walls painted with lime paint cannot be painted over with any other type of paint; the lime paint must be completely removed, which is easily done with a steel brush.
It is important that the pigments are compatible with lime and if more than 5 to 10% is added to pure lime paints, the binding strength of the lime is reduced. The following are considered compatible with lime: titanium white, yellow ochre, red ochre, brown ochre, cadmium yellow, chrome red, chrome green, ultramarine, cobalt blue, green earth, umber, terra de sienna, ferric oxide black, ilmenite black and bone black.
Factory manufactured lime paint has dolomite added to improve its durability, plus a little collagen glue or cellulose paste to improve ease of application and opacity. Water soluble glue is eventually washed out.
Lime paint gets dirty easily in urban environments. It is very sensitive to acids, which break it down to gypsum. It is therefore debatable whether this paint should be used in an area with an acidic atmosphere. The surface underneath is, however, protected from acidic attack, as the lime acts as a sort of sacrificial layer.
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