Finish Coats, Decorative and Specialty Finishes, and Mouldings
Finish and decorative work is where craft shows: texture, sheen, moulding alignment and crisp joints. Expect questions on texture types, veneer and lime finishes, moulding materials, adhesives and cutting technique.
Finish systems
Veneer plaster goes onto a special gypsum base in one or two thin coats and produces a hard, smooth surface; conventional finish plaster is lime putty with gauging plaster or Keene's cement. Lime and Venetian-style finishes are built in thin layers, burnished to a sheen and usually sealed; they need a compatible base with controlled suction.
Textures
Common textures include orange peel, knockdown, sand float, skip trowel, lace or stomp, and acoustic. Knockdown is sprayed or rolled, then flattened with a trowel once it begins to set, so timing controls the look. Skip trowel uses thinned compound and light trowel pressure, leaving base visible through the film. Matching an existing texture means matching compound, tip, pressure and dry time on a sample board, not just the pattern.
Mouldings
Gypsum and plaster mouldings are set with a compatible adhesive, often supplemented by screws into backing, with joints filled in setting compound and sanded. Polyurethane and MDF mouldings need the manufacturer's adhesive and their own joint treatment. Crown is installed by spring angle, and inside corners are coped rather than mitered so out-of-square walls do not open a gap.
Worked example
A repair leaves a 300 mm patch in a skip-troweled wall, and the client wants it invisible under a side light.
Reasoning: first feather the patch to Level 4 or 5 so the plane is flat. Then build texture with compound thinned to the same consistency, the same trowel size and pressure, knocked down at the same set time as the surrounding work. Compare on a sample board at the same lighting angle before committing, because the eye reads contrast in texture before it reads the pattern.
Traps
Finish coat applied too thick, causing craze cracks; troweling lime too long and burnishing unevenly; painting over an unprimed lime finish; adhesive that bleeds through; mitering crown on a crooked wall; filling moulding joints with the wrong compound and sanding a fuzzy edge.