DECAY OF TIMBER 125 



Preservative Processes. — Several processes are in use for preserving 

 timber from decay, such as — 



1. Painting, tarring, varnishing, oiling; 



2. Creosoting, i.e. extracting air and moisture from the wood and 



replacing them with oil of tar, forced into the wood under 

 pressure ; 



3. Impregnating the timber with solutions of certain substances 



such as corrosive sublimate, zinc chloride, copper sulphate ; 



4. Charring the surface of the timber. Timber which is to be 



put into the ground is often charred, as an alternative to 

 tarring. 



Dry Rot. — Dry rot is a disease of timber caused by the fungus 

 Merulius lacrymans, which destroys the fibres of the wood and reduces 

 it ultimately to dry dust. 



The conditions most favourable to the occurrence of dry rot are a 

 warm, moist, still atmosphere, and the presence of green sap in the 

 timber, i.e. the timber not properly seasoned. The fungus soon dies 

 in the presence of plenty of fresh air. 



The germs of the fungus in question are supposed to be brought 

 from the forest in cracks in the timber. Spores from the fungus growing 

 in dry-rot infected wood float about in the atmosphere and, finding a 

 lodgment in sound timber, attack it, provided the conditions are favour- 

 able to the growth of the fungus. In this manner, sound timber may 

 become infected, even though it is not in direct contact with diseased 

 timber. 



The fungus, when of strong growth, looks like mildew on the wood, 

 and gives rise to an unpleasant, musty smell. 



Prevention of Dry Rot. — To prevent dry rot use only thoroughly 

 seasoned wood, and so fix it that the circulation of fresh 

 air around it is as good as possible. 



The tarring, or creosoting, of thoroughly seasoned timber fortifies it 

 against infection. 



Dry rot is particularly apt to attack ground floors. In Chapter VII, 

 the arrangements suitable for ventilating the space under such a floor 

 are described. As a further precaution the wall-plates, joists, sleepers, and 

 the under faces of the flooring boards should be well tarred, the tar 

 being applied hot so as to increase its penetration into the wood. It 

 i3 advisable to have no timber nearer than 6 inches to the surface of 



