---
title: "Good paint characteristics; painting galvanized iron"
subject: "Engineering Chemistry"
chapter: 8
key: "semester_2/engineering_chemistry:paint-galvanized"
source: https://www.bctengineer.com/q/semester_2/engineering_chemistry/paint-galvanized
site: BCT Engineering
---

# Good paint characteristics; painting galvanized iron

Engineering Chemistry · Chapter 8: Lubricants and Paints

- Asked in: 2075 Baisakh, 3 marks; 2073 Magh, 3 marks (asked 2 times)
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_2/engineering_chemistry/paint-galvanized
- Whole chapter: https://www.bctengineer.com/md/semester_2/engineering_chemistry/chapter-8

## Question

Write the characteristics of a good paint and explain the method of application of paint in galvanized iron.

## Short answer

A good paint spreads easily, dries to a hard, elastic, adherent film, resists weathering and chemicals, and is non-toxic. For galvanized iron, clean and etch with dilute acid, apply a zinc chromate primer, then finish with two coats of oil paint or enamel.

## Answer

#### Characteristics of a good paint
1. Easy to apply and spreads uniformly with good covering power (opacity).
2. Dries in a reasonable time to a hard, tough, smooth, elastic film.
3. The film adheres well and does not crack, peel or blister.
4. Good colour and gloss that do not fade.
5. Resistant to weather, water, chemicals and heat.
6. Non-toxic, with a pleasant smell, and cheap.

#### Painting galvanized iron
Fresh zinc coating is smooth and oily, so paint does not stick to it directly.
1. **Clean** the surface: remove grease and dirt with a solvent (mineral spirit) and scrub off any white rust.
2. **Etch** the surface: wash with a mild acid solution, such as dilute acetic acid/vinegar or a copper chloride mordant, so that the surface becomes rough. Alternatively let it weather for several months. Rinse and dry.
3. Apply a **primer** coat of zinc chromate or an etching primer (red lead should not be used).
4. After drying, apply two coats of oil paint or enamel as the **finishing coat**, with drying time between coats.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Why does paint not stick directly to fresh galvanized iron?
   A. The fresh zinc coating is smooth and oily
   B. Zinc reacts violently with the paint oil
   C. Galvanized iron is too rough
   D. Zinc is a magnetic metal
   Answer: A. Fresh zinc is smooth and oily, so the paint has no grip; the surface must be cleaned and roughened. (Key point: Why prime)

2. What is the purpose of washing galvanized iron with dilute acetic acid or a copper chloride mordant?
   A. To add a thicker zinc layer
   B. To remove the paint solvent
   C. To roughen the surface so paint can adhere
   D. To make the surface smoother and glossier
   Answer: C. Etching with a mild acid makes the surface rough, giving the primer a key to grip. (Key point: Etching)

3. Which primer is suitable for galvanized iron?
   A. Zinc chromate or an etching primer
   B. Red lead primer
   C. Bituminous paint
   D. Cement paint
   Answer: A. Zinc chromate or an etching primer is used; red lead should not be used on zinc. (Key point: Primer choice)

4. What is the correct order of steps for painting galvanized iron?
   A. Prime, clean, etch, finish
   B. Etch, finish, prime, clean
   C. Clean, etch, prime, finishing coats
   D. Finish coat, primer, etch, clean
   Answer: C. Grease is removed first, the surface is etched, then primed, and finally two finishing coats are applied. (Key point: Order of steps)

## Related in Engineering Chemistry

- [Paint and requisites of a good paint](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Apaint-requisites-short) — Engineering Chemistry, chapter 8, asked 2×
- [Application of paint on wooden articles](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Apaint-wooden) — Engineering Chemistry, chapter 8
- [Characteristics of good paints](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Apaint-characteristics) — Engineering Chemistry, chapter 8, asked 2×
- [Paint requisites and types of paints](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Apaint-requisites) — Engineering Chemistry, chapter 8

## Related in other subjects

- [Characteristics of a good paint](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acharacteristics-good-paint) — Civil Engineering Materials, chapter 9
- [Paints, oil paint ingredients, painting woodwork](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apaints-characteristics-066bh) — Building Technology, chapter 9
- [Emulsion paint; painting on new woodwork](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apainting-wood-emulsion) — Building Technology, chapter 9
- [Characteristics of good building stones](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Acharacteristics-good-building-stones) — Civil Engineering Materials, chapter 2, asked 9×