A dead bed is a thick, non-bonding layer of mortar or screed on which stones are laid without forming a true mechanical bond between stone and substrate. The term is used in masonry, particularly when natural stone elements are placed on an existing structure.
What makes a bed “dead”?
In a normal mortar bed the mortar bonds actively with the porous substrate. In a dead bed this does not happen:
- The mortar adheres poorly (for example to a smooth or impregnated surface)
- The stone is set too late into a screed that has already begun to harden
- The layer is too thick or too dry to develop adhesion
The result is that the stone is held in place only by its own weight and friction. Under load or vibration, the bond can fail.
Applications
A dead bed occurs in various situations:
- Capstones on garden walls — a thick layer of screed onto which natural stone is laid loose
- Restoration work — when new stones are placed on old, contaminated masonry
- Floors and pavings — natural stone tiles set on a thick mortar bed without adhesive
- Temporary constructions — at scaffolding bricks or infill work
Points to consider
- Check adhesion — a dead bed is not a full bond for load-bearing structures
- Water trapping — water can pool beneath the stone and freeze
- Pre-wetting — a dry substrate draws mixing water from the mortar too quickly
Related terms
- Mortar
- Masonry
- Joint
- Mixing water
- Adhesion
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