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Pointing, plastering defects, oil paint constituents
Short answer
Pointing is needed to protect mortar joints from weather, prevent water ingress, and enhance appearance. Plaster defects include cracks, blistering, peeling, efflorescence, and hollowness. Oil paint constituents are base for opacity, vehicle for binding, pigment for colour, drier for curing, thinner for workability, and extender for bulk.
Why is pointing necessary? What are the defects in plastering works? Explain various constituents of oil paint.
Why pointing is necessary
- Protects the mortar joints from rain, weathering and chemical attack.
- Prevents water from seeping into the wall through the joints.
- Improves the appearance of exposed brick or stone masonry.
- Increases the life of the wall without the need for plaster.
- Cheaper than plastering.
Defects in plastering
- Cracks: caused by shrinkage, poor curing, thermal movement or a poor mortar mix.
- Blistering: swelling of the plaster caused by slaking of lime particles.
- Peeling/flaking: poor adhesion to a dirty, dry or smooth surface.
- Efflorescence: white salts brought to the surface by dampness.
- Hollowness (drummy plaster): poor bond with the background.
- Grinning: joint lines of the masonry show through the plaster.
- Rust stains: from metal or iron embedded in the wall.
- Uneven surface, and popping (small pits caused by unslaked lime particles or pebbles).
Constituents of oil paint
| Constituent | Function |
|---|---|
| Base (white lead, zinc oxide, titanium dioxide) | Gives body, opacity and covering power |
| Vehicle (linseed oil, poppy oil) | Carries the pigment and binds it into a film |
| Pigment | Gives colour |
| Drier (litharge, lead acetate) | Speeds up drying |
| Thinner (turpentine, mineral spirit) | Reduces thickness for easier application |
| Extender/Adulterant (barytes, chalk) | Gives bulk, reduces cost |
✓ Answer checked by Claude Opus 5.5 (high effort)
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