Decorative Mouldings & Arches

MODULE 6: Decorative Mouldings & Arches

This advanced module covers the creation of ornamental plaster features - a specialist skill combining precision craftsmanship with artistic flair. Students will learn both traditional and modern techniques for enhancing architectural spaces.

A. Running Cornices and Coving

1. Understanding the Components

• Cornice: Decorative horizontal molding where wall meets ceiling

• Cove/Coving: Curved transitional molding between wall and ceiling

• Profile Types: Classical (egg-and-dart), Victorian (acanthus leaf), Art Deco (stepped geometric)

2. Installation Methods

Traditional Plaster Method:

• Create a running mold from profile template

• Fix grounds (wooden battens) as guides

• Apply 3-layer system:

1. Backing coat (coarse lime/sand mix)

2. Filling coat (fine aggregate mix)

3. Finishing coat (pure lime putty)

Modern Pre-formed Systems:

• Gypsum-based pre-cast sections

• Adhesive fixing with joint reinforcement

• Seam blending techniques

3. Running Techniques

• Maintain constant speed and pressure

• Keep mold perfectly aligned to grounds

• Work in manageable sections (1-2m)

• Use mitre sticks for clean corner joints

4. Repair & Restoration

• Historic cornice conservation

• Missing section reconstruction

• Surface consolidation methods

B. Forming Arched Openings

1. Arch Types and Applications

• Segmental: Low-rise curve (Victorian doorways)

• Gothic: Pointed apex (ecclesiastical buildings)

• Elliptical: Gradual curve (Georgian features)

• Jack Arch: Straight with curved soffit (industrial style)

2. Construction Process

Traditional Lath and Plaster:

1. Build timber centering framework

2. Nail laths at close spacing (5mm gaps)

3. Apply 3-coat plaster system:

• Pricking-up coat (pushes through laths)

• Floating coat (levels surface)

• Setting coat (smooth finish)

Modern Drywall Method:

• Cut flexible plasterboard to curve

• Use track and stud support system

• Scrim tape all joints before skimming

3. Forming Perfect Curves

• Calculate rise and span accurately

• Use trammel bar for consistent radius

• Specialized tools: French curve rules, arch formers

• Work from keystone outward in symmetrical arches

4. Decorative Arch Treatments

• Applied moldings (archivolt detailing)

• Recessed panels (coffer effects)

• Polished plaster finishes (Venetian plaster)

Assessment Criteria:

• Accuracy of reproduced profiles

• Seamless joint integration

• Appropriate material selection

• Historical accuracy (for restoration work)

This module bridges traditional plastering skills with architectural design principles, requiring both technical precision and artistic interpretation. Students will develop the ability to recreate period features or design contemporary ornamental elements.