covering. Plastic covering is often applied to the fittings and
molded into the shape of the fitting. The plastic covering comes in
bags and is dry. It is mixed with warm water to the consistency of
thick cement and applied with a trowel. When the covering is put on
the pipes and fittings, it should be done thoroughly to get
satisfactory results. Each section of the covering has on one end
an extra length of the jacket. This is to allow a lap over on the
next section to make a tight joint. If the sections need fitting, a
saw can be used and the covering cut to any desired length.

_Magnesia_ covering is employed mostly on steam pipes,
especially high-pressure. This material can be had in the
shape of pipe covering, in blocks, or cement.

_Asbestos air cell_ covering is employed to cover hot-water
circulating pipes. It is constructed of corrugated asbestos
paper. This material is manufactured in the sectional pipe
covering or in corrugated paper form.

_Molded asbestos_ covering is also used on hot-water pipes,
and is manufactured in pipe covering or in blocks.

_Wool felt_ covering is used mostly on hot-water pipes and
makes one of the best coverings. It is lined with asbestos
paper and covered with a cloth jacket.

_Waterproof paper and wool felt_ is used on cold-water pipes
and is made in 3-foot lengths. The covering is lined with
waterproof paper and covered with a cloth jacket.

_Cork._--A heavy cork covering is one of the best coverings
for ice-water pipes, and a light cork covering is used for
cold-water pipes. This covering comes in sections as other
coverings, also in blocks and sheets.

_Hair felt_ is used to prevent pipes from freezing. It comes
in bales containing 150 to 300 square feet of various
thicknesses.

CHAPTER XVI

"DURHAM" OR "SCREW PIPE" WORK. PIPE AND FITTINGS

"Durham" or "screw pipe" work is the name used to denote that the
job is installed by the use of wrought-iron or steel screw pipe. We
speak of a "cast-iron job" meaning that cast-iron pipe was used for
the piping. A completely different method of work is used when
screw pipe is employed for the wastes and vents. When screw pipe is
to be used or considered for use, it is well to know something
concerning the various makes of screw pipe. Nothing but galvanized
pipe is ever used. The value of steel screw pipe and w