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]

Moby Thesaurus II by Grady Ward, 1.0:

46 Moby Thesaurus words for "incrustation":
   blanketing, blocking, blotting out, cementwork, cloaking, clouding,
   coating, coverage, covering, crust, curtaining, eclipse, eclipsing,
   envelopment, enwrapment, enwrapping, eschar, hiding, laying on,
   mantling, masking, obduction, obscuring, occultation, overlaying,
   overspreading, pargeting, pastry shell, piecrust, plasterwork,
   scab, scale, screening, sheathing, shell, shielding, shrouding,
   stalactite, stalagmite, stuccowork, superimposition, superposition,
   upholstering, upholstery, veiling, wrapping