---
title: "Knot treatment in wood painting"
subject: "Civil Engineering Materials"
chapter: 9
key: "semester_3/civil_engineering_materials:knot-treatment-wood-painting"
source: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/knot-treatment-wood-painting
site: BCT Engineering
---

# Knot treatment in wood painting

Civil Engineering Materials · Chapter 9: Paint and Varnishes

- Asked in: 2079 Bhadra, 2 marks
- Video: [How to Protect Wood Before Painting - Knotting Solution vs Zinsser BIN Primer](https://www.youtube.com/watch?v=HeZf7XnYNgg) — Team Huggle
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/civil_engineering_materials/knot-treatment-wood-painting
- Whole chapter: https://www.bctengineer.com/md/semester_3/civil_engineering_materials/chapter-9

## Question

How is knot treated for painting in wood works?

## Short answer

Clean the knot, remove oozing resin, and apply two coats of shellac knotting or aluminium paint to seal it. Fill any depression with putty, sand smooth, then proceed with priming and painting.

## Answer

Knots in timber contain resin that oozes out through the paint and spoils the finish, so they must be treated (**knotting**) before painting.

1. Clean the knot with sand paper and remove loose fibres and dirt.
2. If resin is oozing out, scrape it off or burn it with a hot iron or blow lamp, and clean it again.
3. Apply two coats of **knotting**: a solution of shellac in methylated spirit (or a coat of red lead or aluminium paint) over the knot and slightly beyond it, allowing it to dry between coats.
4. Fill any hole with putty, sand smooth, then apply the primer and paint coats.

This seals the resin and prevents the knot from showing through the paint.

## Check yourself

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

1. Why do knots need treatment before painting?
   A. They are too hard
   B. They absorb all paint
   C. They contain resin that oozes through paint and spoils the finish
   D. They are too dark
   Answer: C. Resin from knots bleeds through the paint, so it must be sealed. (Key point: Reason for knotting)

2. What is the usual knotting solution?
   A. Shellac in methylated spirit
   B. Lime in water
   C. Cement slurry
   D. Linseed oil
   Answer: A. Knotting is shellac in methylated spirit (or red lead/aluminium paint). (Key point: Knotting material)

3. If resin is oozing from a knot, what is done first?
   A. Paint over it
   B. Scrape it off or burn it with a hot iron or blow lamp, then clean
   C. Add a drier
   D. Apply putty directly
   Answer: B. Oozing resin is scraped or burnt off and the knot cleaned before knotting. (Key point: Oozing resin)

4. How is knotting applied?
   A. One coat only on the knot centre
   B. Two coats over the knot and slightly beyond, drying between coats
   C. Mixed into the primer
   D. Applied after the finishing coat
   Answer: B. Two coats are applied covering the knot and slightly beyond, with drying between. (Key point: Application)

## Related in Civil Engineering Materials

- [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

## Related in other subjects

- [Building: excavation, wood frames, enamel paint](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Abuilding-i-enamel-doors) — Estimating and Costing, chapter 6
- [Emulsion paint; painting on new woodwork](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apainting-wood-emulsion) — Building Technology, chapter 9
- [Building: excavation, PCC, brick, wood work](https://www.bctengineer.com/question.md?key=semester_7%2Festimating_and_costing%3Abuilding-f-fig3-four-items) — Estimating and Costing, chapter 6
- [Paints, oil paint ingredients, painting woodwork](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apaints-characteristics-066bh) — Building Technology, chapter 9