The Collaborative International Dictionary of English v.0.48:

Incrustation \In`crus*ta"tion\, n. [L. incrustatio: cf. F.
   incrustation. See Incrust.]
   [1913 Webster]
   1. The act of incrusting, or the state of being incrusted.
      [1913 Webster]

   2. A crust or hard coating of anything upon or within a body,
      as a deposit of lime, sediment, etc., from water on the
      inner surface of a steam boiler.
      [1913 Webster]

   3. (Arch.) A covering or inlaying of marble, mosaic, etc.,
      attached to the masonry by cramp irons or cement.
      [1913 Webster]

   4. (Fine Arts) Anything inlaid or imbedded.
      [1913 Webster]

WordNet (r) 3.0 (2006):

incrustation
    n 1: the formation of a crust [syn: incrustation,
         encrustation]
    2: a hard outer layer that covers something [syn: crust,
       incrustation, encrustation]
    3: a decorative coating of contrasting material that is applied
       to a surface as an inlay or overlay [syn: incrustation,
       encrustation]