carefully brushed into the openings
between the larger stones by means of heavy brush brooms. This is an
exceedingly important part of the work and often a much neglected part
of the construction.

The surface is then covered with a second application of bituminous
material, somewhat less in quantity than required for the first
treatment and the surface again covered with stone chips and brushed.

The surface is then thoroughly rolled and is ready for traffic.

=Patching.=--As in the case of surface treatments, there are likely to
be places that, on account of defects in the construction, will fail
soon after the road is placed under traffic. These will quickly
enlarge unless they are repaired promptly. The repairs are made by
loosening the stone in the area affected and adding new stone as
needed and then pouring on the necessary amount of bituminous material
to coat the stones. Allowance must be made for the compression of the
material by tamping so that a depression does not result. The stones
are carefully tamped to place and covered with chips which are also
tamped.

=Characteristics.=--The penetration macadam is a surface well adapted
to motor traffic if the individual vehicles are not too heavy. It is
likely to squeeze out of shape under motor truck traffic, becoming
seriously uneven and uncomfortable for traffic. Its durability is
materially affected by the construction methods followed.

III. Hot Mixed Macadam

The wearing course of the mixed macadam is composed of graded broken
stone or gravel and a bituminous binder. Usually the bituminous
material only is heated prior to the mixing, but sometimes the stone
is also heated.

=Foundation.=--The lower course, which serves as the foundation, is
either broken stone macadam, gravel or concrete.

Where a foundation of broken stone is used, it is constructed of the
materials and in the manner described for the foundation of the
penetration macadam. Quite often a badly worn macadam or gravel road
is used for the foundation and a new wearing course provided by adding
a mixed macadam surface. If such is the case, the old surface is
worked over so as to restore the shape sufficiently and to insure that
it is everywhere of sufficient thickness.

Portland cement concrete is sometimes used as a foundation for the
mixed macadam, but not often. Usually if the traffic is of a character
requiring a concrete foundation, it is desirable to use a better
wearing cours