"When paint blisters, the cause is usually attributed to dampness, and it is perhaps true that more trouble of this character on new buildings can be traced to wet or unseasoned lumber or fresh plastering, than to any other cause, and on old buildings to bad roofs, leaky gutters, broken down spouts and wet basements. There are so many chances for dampness to get under the paint of either new or old buildings that it naturally follows there would be more blisters from this cause than from all others.

As to buildings being in the foregoing condition, the weather before and during the time the paint is applied has much to do with it.

Dampness causing blistering of paint is more easily detected than any other condition. This is especially true where the dampness comes from wet plastering, as the blisters will be full of discolored water which stains the paint when they break, and upon removing the paint over the blisters it will be found that there is very little, if any, paint or oil left in the grain of the wood. When examining surfaces where the water or dampness is not perceptible at the time of the examination, it is safe to assume, without fear of an error in judgment, that dampness has been the cause of the trouble, but there are also many other causes for paint blistering which are often laid to the foregoing.

Where linseed oil has been used from the bottom of a tank and the settlings or foots are mixed with the paint, it will cause blistering. This has the appearance of dampness, there being spots where the paint has not penetrated and the surface is almost bare. This paint will sometimes pull away in large blisters, the underneath of which show that the paint has adhered to the surface but contained something which would not allow of solid drying. This trouble can be attributed to non-drying mucilaginous matter which separated from the linseed oil and did not allow of uniform penetration, binding or drying. Such blisters are invariably oblong and follow the grain of the wood.

New linseed oil will often cause the paint to blubber in very warm weather, these blubbers causing small blisters, that is attributed to the moisture in the oil which the heat draws out in the shape of different sized blubbers, breaking and forming small blisters when the paint is dry.

Paint mixed with rosin oil will blister under extreme heat. Paint applied over old work blisters more often from the application of excessive oil coats than from any other cause outside of dampness. As stated before, dampness is easily traced in either old or new work. Numerous coats of oil paint will often blister very soon after the paint has been applied. The back of these blisters will show that the paint has at one time been dry and was hard enough to hold to the surface, but when paint was applied over it, it could 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 re fleet 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 misat-tributed to leaky roofs, gutters or like causes.