CHAPTER IX 

 WOOD-FINISHING AND PAINTING 



80. Purpose of Wood-Finishing. With few exceptions, 

 all woodwork, whether exposed to the weather or used under 

 cover, is given some sort of surface finish. The object of 

 wood-finishing is twofold, viz.: 



First, to preserve the wood. All wood is porous and, con- 

 sequently, absorbs moisture. With the change of tempera- 

 ture and amount of humidity in the atmosphere, the quantity 

 of moisture taken up by wood will vary. The change in the 

 moisture content of wood causes a change in its shape, known 

 as warp (the word used for buckling) and wind (the word used 

 for twisting). 



The absorption of moisture by wood is accompanied by 

 swelling. As wood dries, it shrinks, thus causing checks and 

 cracks. 



Second, to decorate the wood. Decoration may be natural 

 or artificial. Any substance such as oil or wax which, when 

 applied to the surface of wood, brings out its natural mark- 

 ings and colorings, is regarded as a natural decorative agent. 

 Any substance such as colored stain or paint, which covers 

 the grain of wood when applied to it, may be made a deco- 

 rative agent, but is considered artificial, as it changes the 

 natural appearance. 



81. Method of Preservation. Both the natural and 

 artificial wood-finishing agents serve to seal the pores of the 

 wood . All stains have a tendency to enter the wood fibre and 



97 



