16 BULLETIN 894, U. S. DEPARTMENT OF AGRICULTURE. 
proofed building paper and felt will last only a short time. Sheathing 
quilts composed of some insulating material sewed between sheets of 
paper will deteriorate very rapidly, and most of the other insulating 
materials intended for ordinary building work are of little value and 
short lived. Plaster, where used, should be of cement, not lime. 
If possible it should be somewhat porous and elastic. Canvas used 
for baffles over the lumber pile gives long service. Where used for 
doors, it should be waterproofed. Wood is a very good insulator, 
and is satisfactory around doors or other places even where there is 
considerable moisture. Strips of felt placed around the door jambs 
make a very good joint to prevent leakage, and are easily replaced 
when they become "dead." Such strips should last about two 
years. 
PAINTS AND COATINGS. 
The paint used for inside work hi kilns should be capable of stand- 
ing high temperatures under moist conditions without softening, 
flaking, moulding, or otherwise deteriorating. Some paints become 
dull, chalk, and rub off. Others retain their luster and serviceability 
for a year or more. A high melting asphaltum paint is excellent not 
only for the iron pipes, but also for the steel supports and rails, side 
walls, and ceilings, whether of wood, brick, tile, or concrete. 
The pipes and ironwork should be kept well protected against rust 
by yearly painting and frequent retouching where necessary. White 
lead and linseed oil paints do not last under dry kiln conditions. 
Red lead and linseed oil may be used for iron work. 
HEATING INSTALLATION. 
GENERAL TYPES OF SYSTEMS. 
The source of heat in most dry kilns is steam, distributed through 
a high pressure, low pressure, or vacuum system. If the pressure 
carried is over 10 pounds, the system is called a high-pressure system; 
if less than 10 pounds a low-pressure system. 
Vacuum systems require special apparatus and patented fittings, 
and their success depends largely upon the working of such special- 
ties. As vacuum systems are usually patented and in most cases 
installed by the owners of the patents, their merits will not be dis- 
cussed here. 
Vacuum and low-pressure steam systems are usually used for kihis 
where the maximum temperature desired is below 150° F. and high- 
pressure systems for higher temperatures. 
If available, low-pressure exhaust steam is the most economical 
method of heating low- temperature kilns. Such exhaust steam is 
available only during the working hours of the plant, however, and 
to avoid shutting down the kilns when the plant is not in operation 
the system should be connected through pressure regulating valves 
directly with a boiler in which steam is , maintained continuously. 
Such a by-pass is illustrated on figure 7. 
