The Collaborative International Dictionary of English v.0.48:

Waterproofing \Wa"ter*proof`ing\, n.
   1. The act or process of making waterproof.
      [1913 Webster]

   2. Same as Waterproof, n., 1.
      [1913 Webster]

WordNet (r) 3.0 (2006):

waterproofing
    n 1: the act of treating something to make it repel water [syn:
         waterproofing, sealing]
    2: a coating capable of making a surface waterproof