10.4.4.1 Smooth-Surfaced Roofs. Smooth-surfaced roofs are
relatively easy to inspect visually and repair but they require
periodic recoating with cutbacks or emulsions. Smooth-surfaced
roofs are not as durable as aggregate-surfaced roofs and should
be considered only where aggregate-surfaced roofs have some
disadvantages (e.g., at airports, structural considerations,
etc.). Coatings can be a cost-effective way of extending the
useful life of a bituminous built-up membrane. However, do not
recoat if: (a) membrane is dry, brittle or delaminated; (b)
system contains wet insulation or other subsurface problems; and
(c) roof ponds water. Coatings should be fibrated. Aluminized
coatings can significantly lower the temperature of the membrane,
prolonging its useful life. However, the extra benefits of
"penetrating coatings" (sometimes called resaturants) are
disputed. Their extra cost is seldom justified.
Surfacing with cap sheets or sprayed granules
eliminates the need for periodic recoating but does not provide
as durable a surfacing as aggregate. Cap sheets are prone to
blistering, especially when they are installed in cold weather.
10.4.4.2 Aggregate-Surfaced Roofs. Aggregate surfacing is a
very effective way of armoring a bituminous built-up membrane
against the weather, roof traffic, and other external abuse.
However, when an aggregate-surfaced roof has deteriorated, it is
very difficult to extend its useful life. In very limited cases
it is possible to remove all loose aggregate and dirt, repair all
flashing and membrane defects, then spray a coating of cutback
asphalt or pitch as required onto the existing system and surface
it with new gravel.
10.4.5.1 Emulsions. Emulsion coatings are dispersions of
asphalt or coal-tar in water with an emulsifier agent such as
clay of approximately 50 percent solids. The material should
have a consistency of mayonnaise at the time of application. It
may be brushed or sprayed. Emulsions must be protected from
freezing until all water has evaporated.
10.4.5.2 Cutbacks. Cutbacks have approximately 50 percent
solids suspended in a solvent base vehicle.
(Refer to par. 10.4.1)
Foot Traffic. Require walkway pads to accommodate
periodic traffic over the roofing surface. Since the walkway pad