---
title: "Preparing an older surface for painting"
subject: "Civil Engineering Materials"
chapter: 9
key: "semester_3/civil_engineering_materials:paint-older-surface-preparation"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/paint-older-surface-preparation
site: BCT Engineering
---

# Preparing an older surface for painting

Civil Engineering Materials · Chapter 9: Paint and Varnishes

- Asked in: 2076 Chaitra, 2 marks
- Video: [LEARN: How to Prep Old Paint for New Paint](https://www.youtube.com/watch?v=tNAGU5a4pR4) — Paint Society
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/paint-older-surface-preparation
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-9

## Question

Write the steps of preparing the older surface for painting.

## Short answer

Remove loose or flaking paint by scraping or using a remover, clean the surface, sand glossy areas, fill cracks with putty, treat knots and rust, then prime bare spots before repainting.

## Answer

Preparation of an old painted surface:

1. **Inspect** the old paint: if it is sound and firmly stuck, only cleaning and light rubbing are needed; if flaking, cracked or blistered, remove it fully.
2. **Remove old paint:** Scrape with a scraper or wire brush, or use a paint remover or blow lamp for thick coats.
3. **Clean** dust, dirt, oil, grease, mould and efflorescence with a brush, soap or detergent water, then rinse and let dry.
4. **Rub down** with sand paper (glass paper) to roughen glossy areas and give grip for the new coat.
5. **Repair:** Fill cracks and holes with putty or filler, and sand smooth.
6. **Rust and knots:** Remove rust from metal with a wire brush; treat bare patches and knots with primer or knotting.
7. **Prime bare spots** and then apply the new undercoat and finishing coats.

## Check yourself

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

1. When is only cleaning and light rubbing enough on an old painted surface?
   A. When paint is flaking
   B. When paint is blistered
   C. When old paint is sound and firmly stuck
   D. Always
   Answer: C. Sound, firmly stuck paint needs only cleaning and light rubbing; defective paint must be removed. (Key point: Inspection)

2. Why is the surface rubbed with sand paper?
   A. To roughen glossy areas and give grip for the new coat
   B. To make it shinier
   C. To add paint
   D. To remove rust only
   Answer: A. Roughening gives the new coat a grip. (Key point: Rubbing down)

3. How may thick old coats be removed?
   A. Painting over them
   B. Washing with water only
   C. Applying varnish
   D. Paint remover or blow lamp, with scraping
   Answer: D. Scrape with a scraper or wire brush, or use paint remover or blow lamp for thick coats. (Key point: Thick old coats)

4. How is rust on metal treated during preparation?
   A. Ignored
   B. Removed with a wire brush, then bare patches primed
   C. Covered with putty
   D. Washed with oil
   Answer: B. Rust is wire-brushed off and bare patches are primed. (Key point: Rust and knots)

## Related in Civil Engineering Materials

- [Painting a new plastered surface](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Apaint-new-plastered-surface) — Civil Engineering Materials, chapter 9
- [Painting a new wood surface](https://www.bctengineer.com/question.md?key=semester_3%2Fcivil_engineering_materials%3Apaint-new-wood-surface) — Civil Engineering Materials, chapter 9

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- [Design steps of surface drainage](https://www.bctengineer.com/question.md?key=semester_6%2Ftransportation_engineering_i%3Asurface-drainage-design-steps) — Transportation Engineering I, chapter 4, asked 3×
- [Painting work on metal surfaces](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apainting-metal) — Building Technology, chapter 9, asked 2×
- [FEM steps and geometric modelling](https://www.bctengineer.com/question.md?key=semester_7%2Fmachine_design_ii%3Afem-steps-geometric-modelling) — Machine Design II, chapter 1