01 May 1999
1/ Asphalt. The mechanical spreader application temperature should be such that a
viscosity of 0.075 Pas @ (75 centipoise) can be achieved. Viscosity for hand mopping should be
0.125 Pas (125 centipoise).
2/ Coal Tar Pitch. The mop and mechanical spreader application viscosity should be
0.025 Pas (25 centipoise).
(b) Interply bitumen is applied in a continuous thin film.
(c) Check for uniform interply hot moppings so that nowhere does felt touch felt. Average
interply mopping weight must be within specifications ([49-98 Kg/m2 (15-30 lbs/sq)].
(d) In cold weather require double (circulating) or insulated asphalt delivery lines as well
as insulated asphalt carriers and mop buckets. (Also store felts in a warm enclosure.)
(e) Do not specify coal tar pitch on roofs with slope exceeding 2% (1/4 in.).
(f) Specify asphalt suited to the slope. Type I is preferred on roofs that occasionally pond
water, at least for the flood coat on aggregate surfaced roofs. Type IV may be preferred for hot
climates such as the desert southwest.
(5) Reinforcements. When hot mopped bitumen is used to bond a base sheet to insulation
specify Type III (or in some instances Type IV) asphalt.
(a) Felts are installed with correct headlap, endlap, sidelap and exposure (figure 4-3).
(b) Roofing plies are installed so sidelaps and endlaps do not oppose (buck) water flow.
(c) Require immediate repair of felt laying defects such as fishmouths, blisters, ridges,
splits, or misalignment.
(d) Use a nailed, asphalt coated base sheet for the first ply of built-up roofing membranes
over wet decks (e.g., poured gypsum, lightweight insulating concrete).
(e) Felts are being broomed or squeegeed into the hot bitumen so that a continuous film
of bitumen exists between reinforcing plies. Felts laps must be firmly embedded.
(6) Aggregate Application.
(a) Aggregate application should usually be delayed until an entire roof area is complete
so that the aggregate does not contaminate work in progress. Unadhered aggregate should be
removed from roofs near aircraft tarmacs to avoid wind caused damage.
(b) Provide trafficways or an entire traffic surfacing for roofs subjected to more than
occasional foot traffic.
(7) Nightly Seals. Roof edges and end of day work must be sealed off to protect against
b. Pre-Roofing Conferences. A pre-roofing conference should be held prior to construction.
Representatives of the designer, user, roofing contractor, general contractor, materials manufacturer,
field inspectors and other related subcontractors should be present. See Appendix 4-2 for suggested
formats for pre-bid, preliminary, pre-application, and final inspection. Quality assurance measures
should be discussed including field inspection, roof test cuts, and rejection procedures.