Whitewash is lime and water. It is not paint. It does not form a film. It penetrates the masonry substrate and bonds chemically to the calcium carbonate in the stone or brick, becoming part of the surface rather than a coating on top of it. A freshly whitewashed wall looks almost luminously white. Over years, it weathers to a soft, chalky white with the texture of the masonry reading through.
Matte, slightly chalky, white with the texture and color variation of the substrate reading through. Where the brush overlapped, there are faint striations. Where the masonry is uneven, the whitewash is slightly thicker in the recesses and thinner on the high points. The overall effect is not the flat uniformity of latex paint — it is a surface that breathes and varies.
Traditional whitewash is hydrated lime (calcium hydroxide) mixed with water to a consistency slightly thinner than paint — approximately one part lime to four to six parts water. The mixture is brushed onto damp masonry in thin coats. Three to four coats, each allowed to dry completely between applications, builds an appropriate depth. The lime cures by carbonation — absorbing CO2 from the air and converting back to calcium carbonate.
Whitewash is not permanent in the sense that paint is permanent. It weathers gradually, wearing from the surface in exposed conditions. A whitewashed wall in a protected location holds for decades. In exposed conditions, surface chalking occurs over years and the finish slowly becomes thinner. Refreshing whitewash every five to ten years in exposed conditions is the traditional maintenance approach.
Whitewash is the historically correct masonry finish for New England buildings from the Colonial period through the 19th century. Barn interiors were whitewashed for sanitary purposes and light reflection. Foundation walls, rough stone outbuildings, and interior masonry were all whitewash territory. It is not a painted finish that tries to hide the masonry. It is a treatment that reveals it.
Hydrated lime (Type S mason's lime) is available from masonry suppliers and some building supply dealers. Mix fresh — do not let the mixed whitewash sit more than several hours before use. Do not use agricultural lime (calcium carbonate) or quicklime (calcium oxide). Type S hydrated lime is the correct material.
Type S hydrated lime mixed with water to brushing consistency, applied in three to four thin coats to damp masonry, for whitewashing barn interiors, cellar walls, and rough exterior masonry on traditional New England buildings. Allow each coat to dry before applying the next. The finish is not film-forming and will weather gradually. This is the correct treatment for masonry that should read as masonry.
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