GRAINING OUT.
The peculiar grain showing a condition of the surface which manifests itself after the job is finished arises from certain incompetent practices observed along in the early stages of painting, or from the use of wood not adapted to the needs of vehicle construction, as, for example, sappy or unseasoned wood. It is a principle of fine surfacing, substantiated by experience, that when a carriage body has been perfectly smoothed and leveled by the woodworker, it should be given a few hours, say four or five, before priming. This delay is to give the wood, subjected to unusual pressure during the surfacing process, an opportunity to expand and shape itself into a normal conformation. Upon high grade work it would be a good practice to first level thoroughly and set away in an unquestionably dry atmosphere for a few hours, and then have the woodworker apply a second sandpapering. Then after another interval of a few hours, prime thoroughly inside and out, top and bottom; in fact, wherever moisture might possibly find an entrance.
Graining out may come from priming too closely upon the completion of the woodworker's leveling process; or it may come from the dry wood having been exposed, after the surfacing process, to a "spell" of damp weather. The dry, porous timber absorbs enough wetness to raise the grain to such an extent that nothing short of a resurfacing will restore it to its normal smooth and perfect condition again. This wood, with its erect fibres or grain fairly visible to the eye upon a casual examination, if painted over and finished, dries out in time, and in doing so responds to the natural law of shrinkage.
Shrinkage involves a process whereby the priming, roughstuff, color, varnish, etc., apparently goes in while the grain of the wood goes out. Graining out is often due to a priming coat that is not given adequate time to dry hard and firm. This soft layer of rather slow drying pigment, if sealed from contact with the air prematurely, is a powerful inducement to grain showing. Spongy, porous roughstuff, deficient in resinous matter and weak in its binding property, is also often responsible for graining out. Good reliable priming, lead and roughstuff coats, allowed to dry thoroughly, each and all of them, arrest the graining out tendency. Improperly seasoned wood is a prolific producer of grained out surfaces.
Moisture confined under a body of paint and varnish is bound to make its exit right speedily, and this it does by voraciously sucking the paint and varnish material in and pushing the grain of the wood out.