Question 1
(a)List any six primers used in decorative painting.
(b) Explain any three of the following terms:
(i) pretreatment;
(ii) galvanizing;
(iii) mill scale;
(iv) acid pickling.
Observation
Some candidates answered the question correctly, while others answered the question out of context. The candidates performance was fair. They were expected to provide the following answers to the question:
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- Red lead primer;
- Calcium plumbate primer;
- Zinc chromate primer;
- Metallic lead primer;
- Red oxide primer;
- Zinc rich primer;
- Alkyd-based aluminium primer;
- Acrylic primer;
- Pink wood primer;
- Aluminium wood primer;
- Lead free or leadless primer;
- Etch primer;
- Lead based primer;
- Alkaline resisting primer;
- All purpose, universal/multi-surface primer;
- Quick-drying acrylic metal primer;
- Preservative primer;
- Stabilising/solution primer.
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(i) Pre-treatment
It is a method of coating metal before painting to improve the durability of paint by ensuring better adhesion and resisting corrosion.
(ii) Galvanizing
A zinc coating applied on iron or steel to protect it from corrosion.
(iii) Mill scale
- A thin skin layer of iron oxide which covers the surface of steel when it leaves the rolling mill.
- A form of iron oxide which adheres tightly to the new metal in a laminated structure in course of time it gets loose and flakes providing an unstable basis for a paint system.
(iv) Acid pickling
- A method of treating iron or steel by immersion in diluted acids thus protecting it from corrosion.
- A process of removing rust from steel by immersing it in a bath containing acid solution.