---
title: "Paints, varnishes, painting procedures"
subject: "Building Technology"
chapter: 9
key: "semester_6/building_technology:paints-varnish-064j"
source: https://www.bctengineer.com/q/semester_6/building_technology/paints-varnish-064j
site: BCT Engineering
---

# Paints, varnishes, painting procedures

Building Technology · Chapter 9: Finishing works

- Asked in: 2064 Jestha (old course), 16 marks
- Video: [Painting | Constituents | Classification | Types | Process | Defects | Varnish | Tools | BMCP](https://www.youtube.com/watch?v=LTjID4rwEfU) — Mounika Meduri
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/building_technology/paints-varnish-064j
- Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-9

## Question

Define paint and varnishes used in the building. Illustrate the constituents of an oil paint. Describe the painting procedures on; new and old woodworks, metal works and cement surfaces.

## Short answer

Paint: mixture of pigment, vehicle, thinner forms opaque protective film. Varnish: resin in solvent, hard transparent gloss. Oil paint constituents: base (opacity), vehicle (linseed oil), pigment, drier, thinner, extender. New wood: knot, prime, putty, undercoat, finish; old: strip, spot prime; metal: rust removal, red oxide primer; cement: dry plaster, alkali primer, two coats (cement paint cured).

## Answer

#### Paint and varnish
- **Paint:** a mixture of pigment, vehicle and thinner that forms an opaque, coloured, protective film on a surface when dry.
- **Varnish:** a solution of resin (lac, copal, rosin) in a solvent (turpentine, spirit or oil) which dries to a hard, glossy, transparent film. It protects woodwork and brings out its natural grain. Types: oil varnish, spirit varnish, turpentine varnish, water varnish.

#### Constituents of oil paint
| Ingredient | Example | Function |
|---|---|---|
| **Base** | White lead, zinc white, titanium dioxide, red oxide | Gives body, opacity and covering power |
| **Vehicle (carrier)** | Linseed oil, tung oil, poppy-seed oil | Carries the pigment, spreads and dries to a hard film |
| **Pigment** | Iron oxide (red), chrome (yellow), carbon black, ultramarine | Gives colour |
| **Drier** | Litharge, red lead, manganese salts | Speeds up drying of the oil |
| **Thinner (solvent)** | Turpentine, mineral spirit | Makes the paint workable; evaporates after application |
| **Extender (adulterant)** | Barytes, gypsum, china clay | Adds bulk, reduces cost |

#### Painting procedures
##### 1. New woodwork
1. Rub the surface with sandpaper; seal knots with knotting (shellac).
2. Apply a priming coat (red lead with linseed oil); allow 24 hours to dry.
3. Fill holes and cracks with putty; sand smooth.
4. Apply one or two undercoats, sandpapering each after it dries.
5. Apply one or two finishing coats of the final colour.

##### 2. Old woodwork
1. Remove old peeling paint by scraping, a blow lamp or paint remover; wash and dry.
2. Rub down with sandpaper and fill defects with putty.
3. Spot-prime bare areas.
4. Apply undercoat and then finishing coats as for new work.

##### 3. Metal work
Remove rust and scale with a wire brush or sandpaper; apply a red oxide or zinc chromate primer; apply an undercoat after 24 hours; finish with one or two coats of enamel or synthetic paint.

##### 4. Cement/plastered surfaces
The plaster must be dry (3-4 weeks old). Remove dust and efflorescence, apply an alkali-resistant primer, fill defects with wall putty, and apply two or more coats of emulsion, distemper or cement paint (wetting the surface before cement paint and curing it afterwards).

## Check yourself

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

1. Varnish is
   A. A resin solution drying to a hard transparent glossy film
   B. Cement
   C. Opaque paint
   D. Putty
   Answer: A. Brings out wood grain. (Key point: Varnish)

2. For metal works the primer is
   A. Putty
   B. Red oxide or zinc chromate after rust removal
   C. Shellac
   D. Cement primer
   Answer: B. Prevents rust. (Key point: Metal painting)

3. Before painting cement surfaces
   A. Wet with oil
   B. Use red lead
   C. Plaster must be dry 3-4 weeks and alkali-resistant primer applied
   D. Paint at once
   Answer: C. Fresh alkaline plaster. (Key point: Cement surface)

4. For old woodwork
   A. Paint over loose paint
   B. Use only varnish
   C. Skip priming entirely
   D. Remove peeling paint, rub down, spot prime bare areas, then coats
   Answer: D. Preparation first. (Key point: Old wood)

## Related in Building Technology

- [Paints, oil paint ingredients, painting woodwork](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apaints-characteristics-066bh) — Building Technology, chapter 9
- [Painting on new and old woodwork](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apainting-new-old-wood) — Building Technology, chapter 9, asked 2×
- [Pointing, plastering defects, oil paint constituents](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apointing-plaster-defects-paint) — Building Technology, chapter 9, asked 2×
- [Emulsion paint; painting on new woodwork](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apainting-wood-emulsion) — Building Technology, chapter 9
- [Painting work on metal surfaces](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apainting-metal) — Building Technology, chapter 9, asked 2×
- [Ingredients of an oil bound paint](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aoil-paint-ingredients) — Building Technology, chapter 9

## Related in other subjects

- [Paint and its constituents](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Apaint-constituents) — Engineering Chemistry, chapter 8
- [Paint requisites and types of paints](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Apaint-requisites) — Engineering Chemistry, chapter 8
- [ESL of new machine; when to replace old](https://www.bctengineer.com/question.md?key=semester_6%2Fengineering_economics%3Aeconomic-service-life-new-machine-old) — Engineering Economics, chapter 5
- [Filter definition and denormalization from ωold to ωnew](https://www.bctengineer.com/question.md?key=semester_5%2Ffilter_design%3Afilter-normalization-frequency-change) — Filter Design, chapter 1