Repairs & Restoration

MODULE 5: Repairs & Restoration

This module focuses on repairing damaged plasterwork and specialized techniques for historic/lime plaster restoration, essential for maintenance and conservation projects.

1. Patching Damaged Plaster

Assessment & Preparation

• Identify the Cause:

• Moisture damage (peeling/blistering)

• Impact cracks (structural movement or physical damage)

• Poor original application (delamination)

• Tools Required:

• Hawk and trowel

• Scraper/wire brush

• Plasterer’s rule

• Mixing bucket

Step-by-Step Patching Process

1. Remove Loose Material:

• Cut back to solid substrate with a sharp scraper

• Undercut edges for better adhesion

2. Prepare the Surface:

• Brush out dust and apply PVA (5:1 water) or bonding agent

• For deep holes (>10mm), use mesh tape as reinforcement

3. Application:

• Small patches: Apply finishing plaster in thin layers

• Large areas: Build up with bonding coat first, then finish plaster

• Feather edges smoothly into existing plaster

4. Finishing:

• Polish with a damp sponge for seamless blending

• Allow to dry slowly (cover with polythene in dry conditions)

2. Fixing Cracks and Holes

Hairline Cracks (<1mm)

• Solution:

• Rake out with a knife

• Fill with flexible acrylic filler

• Sand smooth when dry

Structural Cracks (>2mm)

• Repair Method:

1. Cut back crack in a "V" shape

2. Fill with lime mortar or elastic repair mortar

3. Reinforce with scrim tape before skimming

Holes (Nail/Screw Damage, Deep Gaps)

• Small Holes:

• Fill with ready-mixed filler in layers

• Large Holes:

• Pack with expanding foam (trimmed flush)

• Apply hardwall plaster as base coat

• Finish with multi-finish skim

3. Working with Heritage/Lime Plaster

Why Lime Plaster?

• Breathable (allows moisture evaporation)

• Flexible (accommodates building movement)

• Historically accurate for period properties

Types of Lime Plaster

1. Non-Hydraulic Lime:

• Air-curing (used indoors)

• Slow setting (weeks to fully cure)

2. Hydraulic Lime (NHL 2.0, 3.5, 5.0):

• Sets with water (faster cure)

• Higher strength grades for different applications

Restoration Techniques

• Mixing:

• Lime putty + sharp sand (3:1 ratio typical)

• Add animal hair for reinforcement in base coats

• Application:

• Apply in thin layers (max 5mm per coat)

• Keep damp for 7+ days (prevents cracking)

• Finish with fine lime putty skim for smoothness

Common Challenges & Solutions

Key Takeaways

• Modern repairs often use gypsum-based materials for speed

• Historic buildings require lime to preserve authenticity

• Crack repairs must address underlying causes (movement/damp)

• Feathering edges is critical for invisible repairs