External masonry paints

Although limewashes are increasingly being used in conservation, the majority of paints used on external masonry surfaces nowadays will be water-based emulsions. In the past, oil-based paints have been used on external masonry surfaces and this has led to various problems. For example, there can be a reaction between the lime/cement-based render and the paint, leading to flaking and cracking. The oil-based paints are less porous than their water-based alternatives and any moisture getting under the paint can become trapped behind the relatively impermeable paint – pushing the paint off the surface. Nowadays, special high-performance emulsion paints are commonly used. These differ from emulsion paints for internal wall surfaces as they contain fungicides and other additives to accommodate a greater degree of movement of the substrate and provide greater durability. Dusty or friable surfaces must be primed with a stabilising solution prior to the application of two coats of the paint. They tend to be matt (although gloss and semi- gloss options are available), come in a huge range of colours and are applied by brush, roller or spraying. Once applied, redecoration at regular intervals will be required.