Page:Cyclopedia of Painting-Armstrong, George D (1908).djvu/160

152 not stand the tension or pull of the other coats. This is caused by numerous coats of oil paint which do not thoroughly cement together and form a solid foundation. This can be proven by the backs of the blisters which often have glossy spots that would not show had the coats of paint thoroughly cemented or adhered. Other parts of the blisters show gummy points, proving the paint had once been cemented together in spots. This also shows that the paint was over-elastic and had pulled away from the surface by the heat which broke the coats apart. This latter trouble is sometimes called a splitting of the paint. An excess of oil on a hard surface like ochre priming, where there has not been sufficient penetration, will cause the paint to blister on protected parts of the building, such as underneath porches, etc. This trouble is very hard to understand, but the true cause is excessive heat on a porch or veranda floor, reflecting on the sides of the building, causing blistering or the raising up and breaking loose of the paint from the under-surface, this is especially true where the sun reaches porches and verandas which have an enclosed end, preventing free circulation of air and causing intense heat.

Blistering sometimes takes place from excessive painting on the sides of buildings where the sun does not reach. This is caused by radiation of the heat, which is very intense at certain times of the day, and no free circulation of air, also from stone or cement walks which become very hot from the rays of the sun, radiating this heat and blistering the paint for some distance above these walks. Freshly painted veranda floors will reflect enough heat on the side of a building to cause the paint to blister and break away. Veranda ceilings will sometimes blister. The cause can be traced to water which has been thrown on the floor or to pools of rainwater which reflect the heat of the sun on the ceiling, forming a lens the same as would a convex glass if laid in the same position. This reflection will cause the paint to blister on ceilings and the trouble is often misattributed to leaky roofs, gutters or like causes.