Plaster and drywall compound (joint compound) are often confused but serve different purposes:

Plaster creates a finished wall surface, while drywall compound is used to finish joints between drywall panels. Plaster is generally more durable but requires more skill to apply.

Plaster drying time varies significantly by type, thickness, and environmental conditions. Here’s a general guideline:

• Gypsum Plaster:
  • Surface dry: 24-48 hours
  • Ready for painting: 7-14 days
  • Full cure: 21-28 days
• Cement Plaster:
  • Initial set: 2-6 hours
  • Surface dry: 24-48 hours
  • Full cure: 28 days minimum
• Lime Plaster:
  • Initial set: 2-3 days
  • Carbonation begins: 7-14 days
  • Full carbonation: 1-2 years (continues improving)
• Clay Plaster:
  • Surface dry: 1-3 days
  • Fully dry: 7-14 days
  • No chemical cure needed

Factors affecting drying time: Temperature (ideal 10-25°C), humidity (ideal 40-60%), air circulation, plaster thickness, and substrate absorption rate. Never accelerate drying with heaters or dehumidifiers as this can cause cracking.

Yes, you can plaster over existing plaster, but proper preparation is essential for success:

1. Assess Condition: Check for loose, cracked, or crumbling areas. Tap the surface – hollow sounds indicate delamination.
2. Prepare Surface:
   • Remove loose material with scraper or wire brush
   • Wash with TSP (trisodium phosphate) to remove grease and dirt
   • Rinse thoroughly and allow to dry
3. Improve Adhesion:
   • Score the surface with a utility knife or grinder
   • Apply a bonding agent or plaster primer
   • For glossy surfaces, sand to create a mechanical key
4. Consider Weight: Adding more plaster increases weight on lath or substrate
5. Match Materials: Use compatible plaster types (don’t put cement plaster over gypsum)

When NOT to plaster over existing plaster: If there’s significant damage, water damage, mold, or the substrate is failing. In these cases, remove old plaster completely and start fresh.

For best results, consult a professional plasterer when dealing with historical plaster or complex situations.

Venetian plaster (Marmorino) is a specialized decorative finish, while regular plaster is primarily functional. Key differences:

Venetian plaster creates a luxurious, durable finish that develops a patina over time. Regular plaster provides a practical surface for painting or wallpapering.

Plaster crack repair techniques vary based on crack type and size:

• Hairline Cracks (<1mm):
  1. Clean crack with brush or vacuum
  2. Apply flexible caulk or specialized crack filler
  3. Smooth with finger or putty knife
  4. Paint over when dry
• Small Cracks (1-3mm):
  1. Widen crack slightly with utility knife (create V-shape)
  2. Dampen crack with water spray
  3. Fill with setting-type joint compound or plaster patching compound
  4. Apply mesh tape for reinforcement if needed
  5. Sand smooth when dry
• Large Cracks or Gaps (>3mm):
  1. Remove loose plaster around crack
  2. Undercut edges to create mechanical key
  3. Apply bonding agent to edges
  4. Fill with plaster patching compound in layers
  5. Use reinforcing mesh for gaps wider than 6mm
  6. Finish with skim coat of joint compound
• Recurring Cracks (structural movement):
  1. Consult structural engineer if cracks reappear
  2. May need to install control joints or expansion joints
  3. Use flexible crack-bridging products
  4. Consider plaster type that accommodates movement (lime plaster)

Pro tip: For historical plaster, use compatible traditional materials (lime plaster) rather than modern compounds to maintain authenticity and compatibility.

For bathrooms and wet areas, moisture resistance is the primary concern. Recommended plasters:

1. Cement Plaster (Best for showers/wet rooms):
   • Mix with waterproofing additives or polymer modifiers
   • Apply over cement board or properly prepared masonry
   • Can be finished with tile or waterproof paint
   • Requires proper curing (keep damp for 7 days)
2. Water-Resistant Gypsum Plaster (For general bathroom areas):
   • Contains additives to resist moisture
   • Not suitable for direct water exposure (showers)
   • Apply over moisture-resistant drywall (green board)
   • Finish with bathroom-grade paint
3. Traditional Lime Plaster with Tadelakt Finish (Luxury option):
   • Moroccan technique using special lime plaster
   • Polished with olive oil soap to create waterproof surface
   • Requires specialist application and maintenance
   • Beautiful natural finish but high maintenance
4. Acrylic Polymer Plaster (Modern alternative):
   • Ready-mixed synthetic plaster with excellent water resistance
   • Flexible to accommodate building movement
   • Available in various textures and colors
   • Easy to clean and maintain

Critical considerations: Always install proper waterproof membrane behind plaster in wet areas, ensure adequate ventilation to prevent condensation, and use appropriate sealants at joints and corners. For shower areas, cement plaster with tile is generally the most reliable and durable option.