I was searching for information about stone foundations, and came across your article. We have a very old bank barn with the lower level divided into stalls. The stone foundation doesn’t have the mortar coating you describe, but some remaining white paint. It’s the same paint that’s on the beams and boards above. Can we just repaint, or do we need to apply a mortar coating? What type of paint should we use? Thanks.
In my experience, whitewash was very common on the interior of barns and other old building foundations. It has also been used on other interior walls and was commonly used to brighten up the interiors of fireplaces. The exteriors of entire barns, other outbuildings and even some historic homes have also been treated with whitewash. I remember reading that it was once applied to the fence of Tom Sawyer’s Aunt Polly.
Whitewash is really a limewash (lime and water) with an additional ingredient like chalk, glue, or flour. There have been many recipes throughout history that include other additives. Adding linseed oil, milk, or egg may be an attempt to make the coating perform more like paint. Adding Portland cement may be for better adhesion or to reduce permeability. I’m not sure why some recipes call for mixing with salt, alum, flour, molasses, or urine. Earth pigments, brick and coal dust, and even animal blood have been known to be used to tint the coating. I’ve never tried anything but the two basic ingredients of limewash.
Limewash and whitewash has been applied to stone and brick walls, rendered (stucco coated) buildings, wood siding, logs, plaster and adobe. Its widespread use can be primarily attributed to its availability and low cost, but there are other benefits. It’s nontoxic to people and animals and has no noxious fumes–unless you add something nasty to the mix. It’s breathable, allowing damaging moisture vapor to escape easily from old building products. It also reflects light very well due to the calcite crystals that form. This is probably why it was applied to so many dimly lit interiors of farm buildings and old basements.