The Technique of FURNITURE MAKING

Fire resistance of wood

Although wood might appear to be one of the most inflammable of materials, some species, notably crab wood, jarrah, iroko, padouk and teak, are very resistant, and all woods of large dimension char outwardly, cutting off the supply of oxygen necessary to support combustion. However, built-in fixtures in exhibition-work, public buildings, etc. are sometimes required to be fireproofed, or composed of fire-retardant materials. Plywoods and chipboards in fire-retardant quality can be obtained to special order; or the completed product can be coated with special paints or clear varnishes, or treated with various chemical preparations, the most widely used of which is ammonium phosphate. Alternatively, plywood panels or partitions can be interleaved with plasterboard or soft asbestos to give a 'one hour' standard resistance.

It is, or should be, the responsibility of the buyer or his agent to specify precisely the degree of resistance required, and the materials or treatment to be used; but the terms 'fire­proof or 'fire-resistant' should not be accepted without qualification, otherwise they may be liable to serious misconstruction. It is usually more correct to claim that a combustible material suitably treated is 'fire-retardant' only.

Defects

Every tree is a prey to defects from the moment it emerges as a seedling to the last stages of seasoning, and these defects can be innate (inherent vice), such as the characteristic natural shrinkage of wood; acquired defects occasioned by seasonal checks, insect and fungal attack, etc.; and artificial defects caused by incorrect sawing and seasoning. As, however, any one defect may arise from several causes it is more convenient to classify them as natural or artificial.