I am sure you have run into specifications that call for a “bituminous” coating to be applied in the back of hollow metal frames. Bituminous coating is a coating containing bitumen, any of various flammable mixtures of hydrocarbons and other substances occurring naturally or obtained by distillation from coal. The mixture takes on the form of a viscous, black sticky tar-like substance.
It is most commonly specified for corrosion protection but is also used for sound control. It is suggested that automotive undercoating would be a more progressive replacement. If you are a specifier, here is a link to learn more about this alternative – Types of vehicle undercoating
Due to its flammable nature, this coating cannot be used on fire rated openings. It will void the label unless the frame was tested with the bituminous coating.
The Steel Door Institute recommends that this coating not be applied to frames prior to their arrival at the job site. The coating never fully dries and may leave a dark residue on anything it touches.
The following is from the SDI Series – Industry Alerts 127J
ANSI A250.8-2003 (also 1998) limits factory applied coatings to either factory prime finish (2.1.3) or factory-applied finish paint (2.1.4).
For corrosion protection, ANSI A250.11-2001 paragraph 2.2 clearly states that “the contractor responsible for installation” applies corrosion resistant coatings only where specified for anti-freezing agents in plaster or mortar.
For sound control purposes, it is less damaging to the frame finish and more expedient for “the contractor responsible for installation” to extend the insulation material used in the adjoining wall into the frame. This creates an unbroken barrier to the passage of sound.
For our industry, bituminous coatings are usually excluded from bids and are done “by others”, whoever that is! Be sure to allow for extra time and have frames on jobsite a few days earlier than needed.