Cyclopedia of Painting/Priming
PRIMING.
This is the most important paint coat applied to any surface. It must fill and satisfy the surface and leave a foundation upon which future paint coats can be successfully built. It holds the same relative position in painting as does the foundation of a house in building. It must last and successfully hold the superstructure as long as it remains. It must carry sufficient linseed oil to not only satisfy the surface but bind or hold the pigment to the surface. It must carry sufficient turpentine to cause penetration and assist in forcing, by absorption, the oil and pigment into the surface. The formation of the pigment must be such as to allow of penetration into the surface, and above all, the primer must be well and evenly brushed out and into the surface.
The common idea that anyone can prime a building is a serious mistake. The priming coat offers the best opportunity for judging a painter's work. If he is a capable, careful man he will use as much or more care in applying this coat as he would in the application of the second or third coat. He will brush the paint into the wood, satisfying the soft grain, and carefully brush the hard grain where there is less absorption, leaving an even, uniform coating.
It is impossible to erect a frame building and have all of the timber of the same absorbing qualities. The sapwood absorbs paint more readily than the heartwood, which is of a harder grain. This fact does not necessitate a different reduction for each kind of grain in the same lumber, but it does necessitate the painter's properly applying and brushing out the paint.
In priming soft wood, the paint should be applied with a full brush and enough paint used at all times to satisfy the surface. It should be well brushed and especially on the harder grain to assist or force the paint into this close grain and remove by hard brushing any surplus paint that remains on the surface.
On hard or close-grained wood a medium full brush should be used in applying the paint, as this class of wood does not possess the absorbing properties of softer woods, but requires more brushing in order to force a sufficient amount of oil and binder into the wood and at the same time not leave an excess of paint on the surface.
If the priming coat is of the proper consistency, carrying sufficient pigment to fill and hide the grain, and well brushed into the grain of the wood, most of the absorption will have ceased with this coat and no excess of pigment left on the surface. This thin coat will allow the second coat to penetrate through and satisfy any part of the wood which was not fully filled at the time of priming, also allow the second coat to bind itself to the wood and priming coat.
An excess of paint on very porous woods will cause peeking or chipping. This heavy coat prevents the oil from penetrating the woods and assists in holding the coat on the surface. The oil and binder in the second coat penetrates into this heavy coat only and does not reach the wood so as to assist in forming a solid coat well bound to the surface.
Paint heavily applied to a hard or close grained surface will dry with a gloss, forming a hard glaze over the surface, into which the second coat cannot penetrate to any depth; it will only fasten itself to the outside of this glaze coat, whereas it should go through to the wood so as to help strengthen the second and subsequent coats.
Do not prime a building and allow it to stand any longer than is necessary in order to thoroughly harden the paint and allow of full absorption. If allowed to weather, the priming coat will become porous and absorb the life of the second coat and there will not be sufficient binder left to properly adhere to the surface.
Never use a cheap primer. While cheap in the first cost, it is without exception the costliest in the end. The primer should be of the best and of the same material as the intermediate and finishing coats.
Dry colors mixed by hand should never be used for priming. All paint pigments are much more bulky in the dry state than when properly handled under pressure and combined with oil. When a mixture is made without pressure the outside particles of the pigment are only coated with the oil or thinners, and when applied to a surface, the wood having a greater attraction for the oil than does the pigment, the surface will absorb the oil from the pigment, leaving a dry, porous coating to which subsequent coats cannot successfully bind.