cradle

A cradle is a temporary wooden framework built to support plaster during the construction of a vaulted ceiling or arched opening. It consists of curved ribs, typically made from timber or metal, arranged to match the profile of the finished vault. The ribs are spaced closely enough that laths, plaster base boards, or metal mesh can be securely fastened across them, creating a base for the wet plaster application.

The structure must be strong enough to carry the dead load of applied plaster, which can reach 8 to 15 pounds per square foot depending on coat thickness. Traditional cradles use wooden ribs made from straight-grained softwood like pine or fir, often arranged in a series of parallel arches. The ribs themselves are held in position by cross-bracing and props that extend to the floor or supporting walls, creating a rigid three-dimensional grid.

Support and shoring

Cradles are fully temporary; they remain in place until the plaster has cured sufficiently to become self-supporting, typically 10 to 14 days for barrel vaults. Posts and adjustable shore props support the main ribs, and these must be carefully sequenced during removal to avoid sudden sagging or cracking of the cured plaster. Some cradles incorporate internal bracing with rods or ties to manage thrust forces from barrel vaults and complex geometries.

The term reflects the function: the cradle literally rocks or holds the plaster in the shape it will permanently keep. Unlike formwork for concrete, which must support material until it reaches structural integrity on its own, a plaster cradle exists only to position and contain the material while it sets and bonds to the lath beneath it.

Modern work sometimes substitutes metal studs and runners for wooden ribs, or uses spray-applied plaster over metal lath that requires less elaborate cradle design. However, traditional timber cradles remain essential for complex barrel vaults, groined vaults, and coved ceilings where curved geometry and aesthetic alignment demand precise framing. The cost and complexity of building a proper cradle can represent a substantial portion of the budget for ornamental plasterwork in heritage restoration or custom finishes.