underbed

English

Etymology

under- +‎ bed

Noun

underbed (plural underbeds)

1. An underlying base that supports a bed or foundation.
   • 1886, Geological Survey of Alabama, Special Report (issue 1, page 182)

     It has an underbed of slate and a cover of hard shales which contains seams of sandstone and form ^[sic] a bluff.

   • 2011, H. Leslie Simmons, Olin's Construction: Principles, Materials, and Methods, page 771:

     An underbed is necessary in unbonded cementitious installations and may be required in some bonded ones.