--- title: "Painting on masonry; causes and remedies of cracks" subject: "Building Technology" chapter: 9 key: "semester_6/building_technology:painting-masonry-cracks" source: https://www.bctengineer.com/q/semester_6/building_technology/painting-masonry-cracks site: BCT Engineering --- # Painting on masonry; causes and remedies of cracks Building Technology · Chapter 9: Finishing works - Asked in: 2071 Bhadra, 8 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/painting-masonry-cracks - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-9 ## Question Explain the process of painting works on masonry surfaces. What may be the causes of cracks occurred in a building and what are remedial measure to cracks? ## Short answer Masonry painting: let plaster cure 3-4 weeks, clean, repair, apply alkali primer and wall putty, then two coats of paint (cement paint wetted and cured). Causes: moisture and thermal movement, settlement, elastic deformation, corrosion, chemical attack, vegetation, earthquakes, poor work. Remedial: hairline – cement slurry; small – rake and mortar; medium – epoxy injection; wide – stitch/jacket; settlement – underpinning. ## Answer #### Painting on masonry surfaces 1. **Preparation:** plaster must be at least 3-4 weeks old and fully dry. Remove dust, oil, loose particles and efflorescence with a wire brush and wash. 2. **Repair:** fill cracks and holes with cement mortar or putty and let them dry. 3. **Primer:** apply an alkali-resistant primer. 4. **Putty:** apply wall putty in two coats; rub down with sandpaper after each. 5. **Painting:** apply two coats of emulsion, distemper or cement paint with a brush or roller. The second coat is applied after 4-6 hours. For cement paint, wet the surface first, and cure the paint for 2 days. #### Causes of cracks in buildings | Cause | How it cracks the building | |---|---| | **Moisture movement** | Bricks, blocks and concrete expand on wetting and shrink on drying; mortar and plaster shrinkage | | **Thermal movement** | Expansion and contraction with temperature in roofs, long walls, parapets | | **Settlement of foundation** | Unequal settlement due to poor or non-uniform soil, wrong foundation level, change in moisture, or inadequate depth | | **Elastic deformation** | Overload, deflection of beams and slabs, bending and shear | | **Corrosion of reinforcement** | Rust expands and splits the concrete cover | | **Chemical action** | Sulphate attack, alkali-aggregate reaction, carbonation | | **Vegetation** | Roots of trees near walls and foundations | | **Earthquake and wind** | Lateral forces on weak walls and joints | | **Poor workmanship and materials** | Poor curing, mix, bonding, early removal of formwork, missing joints | | **Overloading and design error** | Excess load, wrong detailing | | **Fire, vibration** | Heat damage, machine vibration | #### Remedial measures | Crack width | Remedy | |---|---| | Hairline (< 0.3 mm) | Fill with cement slurry or paint-grade filler; fresh plaster | | Small (0.3-1.0 mm) | Rake out, fill with cement-sand mortar (1:3) or polymer-modified mortar | | Medium (1-3 mm) | Epoxy injection or cement grout through packers | | Wide (> 3 mm) | Remove and rebuild, stitching with steel clamps, epoxy mortar, jacketing | | Foundation settlement | Underpinning, grouting, soil improvement | | RCC cracks | Epoxy injection, grouting, jacketing, bonding steel plates | | Roof cracks | Waterproof treatment, expansion joints, sealants | ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Before painting new masonry plaster, what must be true of the plaster? A. It must be at least 3-4 weeks old and fully dry B. It must be freshly applied and damp C. It must be at least 1 day old D. It must be coated with cement paint first Answer: A. Plaster must be 3-4 weeks old and fully dry, and cleaned of dust, oil and efflorescence. (Key point: Surface preparation) 2. What is the correct order of painting operations? A. Putty, primer, repair, paint B. Repair of cracks, alkali-resistant primer, putty, paint coats C. Primer, repair, putty, paint D. Paint, putty, primer, repair Answer: B. Cracks are filled first, then primer, two coats of putty, then finish coats. (Key point: Order of painting steps) 3. How does corrosion of reinforcement crack concrete? A. Rust shrinks and leaves a void B. Rust makes steel brittle so it snaps C. Rust expands and splits the concrete cover D. Rust dissolves the cement Answer: C. Rust occupies more volume than steel, so it splits the cover. (Key point: Corrosion of reinforcement as crack cause) 4. A 2 mm wide crack is best repaired by: A. Cement slurry B. Raking and 1:3 mortar C. Rebuilding the wall D. Epoxy injection or cement grout through packers Answer: D. Medium cracks (1-3 mm) get epoxy or grout injection. (Key point: Remedy by crack width) ## Related in Building Technology - [Causes and remedies of cracks](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acracks-causes-remedial) — Building Technology, chapter 10, asked 2× - [Causes of cracks in a building](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acauses-of-cracks) — Building Technology, chapter 10, 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× - [Structural vs non-structural cracks and causes](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acracks-struct-nonstruct-causes) — Building Technology, chapter 10 - [Paints, varnishes, painting procedures](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apaints-varnish-064j) — Building Technology, chapter 9 - [Methods of repairing cracks](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Acrack-repair-methods) — Building Technology, chapter 10, asked 3× ## Related in other subjects - [Negative skin friction: causes, effects, remedies](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Anegative-skin-friction-effects) — Foundation Engineering, chapter 8, asked 4× - [Water logging: causes, effects, remedies](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Awater-logging-causes-effects-remedies) — Irrigation and Drainage Engineering, chapter 9, asked 13× - [Global warming: causes, consequences, remedies](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Aglobal-warming) — Engineering Chemistry, chapter 3, asked 2× - [Flexible pavement failures: causes and remedies](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Aflexible-pavement-failure-cause-remedy) — Transportation Engineering II, chapter 4