overlayer

from WordNet (r) 3.0 (2006)

overlayer
    n 1: protective covering consisting, for example, of a layer of
         boards applied to the studs and joists of a building to
         strengthen it and serve as a foundation for a weatherproof
         exterior [syn: {sheathing}, {overlay}, {overlayer}]

from The Collaborative International Dictionary of English v.0.48

Overlayer \O"ver*lay"er\, n.
   One who overlays; that with which anything is overlaid.
   [1913 Webster]