from Seeley and Morse 1976: "The wails of nest cavities were always solid (see 1. Nest "Site, Tree condition) and coated with [waterproof] propolis on their inner surfaces. Figure 7 shows a small area of this propolis coating. In finished nests the propolis layer was thick and completely covered a nest cavity's floor, walls and ceiling to form the propolis envelope drawn in figure 3. The thickness of this layer varied between 0.1 and 2.3 ram, but was generally in the 0.3 to 0.5 mm range. We dissected several unfinished nests and thus observed the intermediate stages in the preparation of nest cavity wails. When combs only partially filled a cavity, the nest cavity's inner surface was solid and smooth with propolis only around the combs. Lower in the cavity, below the level of the combs, a layer of soft, rotten wood coated the cavity walls. This punkwood lining was up to 20 mm thick. Apparently, before bees build combs they scrape the loose, rotten wood off the walls, thereby exposing firm wood which they then coat with propolis."