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Historic Preservation - Technical Procedures


Monel: Characteristics, Uses And Problems

Procedure code:



20Th Century Bldg Materials (Ed. Tom Jester, Nps)




Metal Materials

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Monel: Characteristics, Uses And Problems


This standard includes general information on the characteristics
and common uses of Monel and identifies typical problems associated
with this material along with common causes of its deterioration.


Characteristics of Monel:

-    a nickel alloy containing 65-70 percent nickel, 20-29 percent
    copper, and small amounts of iron, manganese, silicon and

-    discovered due to the efforts of Robert Crooks Stanley, who
    worked for the International Nickel Company (INCO) in 1901;
    the new alloy was named in honor of the president of the
    company - Ambrose Monell

-    stronger than steel

-    malleable

-    resistant to corrosion

-    low coefficient of thermal expansion

-    highly resistant to alkalis

-    improved sanitation

-    fairly inexpensive

-    can be welded, brazed and soldered

-    in the 1920s and 30s, Monel was available in both hot-rolled
    and cold-rolled sheets

-    typical finishes included brightly polished, "hand-forged"
    black, and two-toned

-    in outdoor applications, Monel develops a patina ranging from
    light gray-green to medium brown


-    popular between 1909 and the mid 1950s

-    available in sheet form for architectural applications

-    installed as a sheet roofing membrane in 1908

-    in the late 1920s, Monel was began to be used for grocery
    coolers, countertops, sinks, laundry and food preparation
    appliances, roofing and flashing

-    other uses for sheet and plate Monel were ductwork, flashing,
    gutters and downspouts, mail chutes, laundry chutes, elevator
    fittings, lighting fixtures, and skylights

-    Monel castings were also popular and included grilles,
    rosettes, plaques, handrail fittings, molding, pilasters,
    mullions, and door jambs

-    Monel forgings were used for hardware

-    Monel bar and rod stock were used for window screens, gates,
    public directory boards, railings, and divider strips in
    terrazzo floors

-    other common applications for Monel included tie wire for
    securing lath in plaster walls and suspended ceilings,
    fasteners for tile roofs and anchors for stone cladding

-    Monel began to be displaced by stainless steel in the 1950s,
    as stainless steel could produce the same forms at a lower
    cost (due to use of less nickel)

-    a modified, less expensive use of Monel included laminating a
    thin sheet of Monel to an inexpensive backing material; two
    examples include Monel-clad steel and Monel-laminated plywood

-    Monel is still manufactured by INCO, primarily in the form of
    sheet goods; cast and rolled forms are also available, but are
    extremely expensive


-    Surface discoloration: Can occur from exposure to atmospheric

-    Pitting: Can occur if exposed to stagnant salt water.

-    Corrosion:

    -    nitric oxides and sulfur dioxides, combined with water,
         are very corrosive to Monel.

    -    nitric and nitrous acids can be very corrosive to Monel
         at room temperature

    -    hypochlorites are severely corrosive to Monel if not

    -    Acid and alkaline oxidizing salts, ferric chloride,
         ferric sulfate, cupric chloride, stannic chloride,
         mercuric chloride and silver nitrate are all corrosive to

    -    resistance to sulfurous acid varies depending on climatic

    -    organic acids (acetic and fatty acids) have little to no
         effect on Monel

-    Stress corrosion cracking: Exposure to aerated hydrofluoric
    acid in moist conditions can cause this to occur.

-    Galvanic corrosion: Metals, such as aluminum, zinc and iron
    will corrode when in contact with Monel AND exposed to severe
    weather conditions.  Therefore, use of these metals as
    fasteners for Monel should be avoided.

                         END OF SECTION