Crusto, crustas, crustâre. To parget or playster: to set a cruste vpon. vt Crustare parietes. Plin. Or to rough lay: to pariet walles, or lay thinne shardes of stones vpon walles, as they did in olde tyme.Crustare mala gypso vel cera. Plin. To couer apples with ware to preserue and keepe them.
Lewis and Short: Latin dictionary
crusto, āvi, ātum, 1, v. a. [crusta], to cover with a rind, shell, incrustation, plaster-work, embossed figures, etc. (post-Aug.): mala gypso, Plin. 15, 17, 18, 64: domum marmoribus,