Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
incrustātĭo, ōnis, f. [incrusto], an incrusting of walls, e. g. with plaster, lime, marble, etc. (post-class.): parietis, Dig. 8, 2, 12 fin.; id. 50, 16, 79.