---
title: "Precautions in Schmidt hammer test"
subject: "Concrete Technology and Masonry Structure"
chapter: 5
key: "semester_5/concrete_technology_and_masonry_structure:schmidt-hammer-precautions"
source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/schmidt-hammer-precautions
site: BCT Engineering
---

# Precautions in Schmidt hammer test

Concrete Technology and Masonry Structure · Chapter 5: Testing of concrete and quality control

- Asked in: 2080 Baisakh, 3 marks
- Video: [Rebound Hammer Test | Schmidt's Hammer | A Non Destructive Test on Concrete | Surface Hardness Test](https://www.youtube.com/watch?v=3-ALGTV-Zus) — All About Structural Analysis and Design
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/schmidt-hammer-precautions
- Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-5

## Question

Write the precautions that should be taken while performing the Schmidt hammer test of concrete.

## Short answer

Check the hammer on a standard test anvil (rebound ~80±2). Use a smooth, clean, dry surface on a rigid member ≥100 mm thick. Hold hammer perpendicular; avoid edges, honeycombed areas, reinforcement, and wet/carbonated surfaces. Take ≥12 readings 20–50 mm apart, reject those differing >6 units from mean, and average.

## Answer

Precautions for the rebound (Schmidt) hammer test (IS 13311 Part 2):

1. Check the hammer on the **standard test anvil** (rebound number about 80 ± 2) before and after the test.
2. Select a **smooth, clean, dry surface**; grind rough or plastered surfaces and remove loose scale and finishing.
3. Test a member at least 100 mm thick that is **rigidly held** (a thin or loose member will vibrate and give low readings).
4. Keep the hammer **perpendicular to the surface**; if it is not horizontal, apply the orientation correction.
5. Avoid edges (at least 20 mm away), honeycombed areas, voids, and spots directly over **reinforcement** or aggregate pockets.
6. Take **at least 12 readings** per area, 20 to 50 mm apart, never at the same point twice; reject readings that differ by more than 6 units and average the rest.
7. Do not use on **wet, frozen or carbonated** surfaces without correction (carbonation raises the number), and note the age and moisture.
8. Use the calibration curve with the same type of hammer and concrete, and handle the instrument carefully; clean the plunger regularly.

## Check yourself

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

1. What is checked on the standard test anvil?
   A. Concrete strength
   B. Hammer reading, about 80 ± 2
   C. Member thickness
   D. Carbonation depth
   Answer: B. The anvil verifies the instrument. (Key point: Anvil check)

2. Why must the member be rigidly held?
   A. It speeds up testing
   B. To avoid the plunger
   C. A thin or loose member vibrates and gives low readings
   D. To prevent carbonation
   Answer: C. Vibration absorbs energy. (Key point: Member rigidity)

3. What effect does carbonation have on the rebound number?
   A. Lowers it
   B. None
   C. Makes it zero
   D. Raises it
   Answer: D. Carbonated surfaces are harder, so correction is needed. (Key point: Carbonation)

## Related in Concrete Technology and Masonry Structure

- [NDT importance; Schmidt hammer test](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Andt-importance-schmidt-hammer) — Concrete Technology and Masonry Structure, chapter 5
- [Rebound hammer test](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Arebound-hammer-test) — Concrete Technology and Masonry Structure, chapter 5
- [UPV and rebound hammer tests](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aupv-and-rebound-hammer) — Concrete Technology and Masonry Structure, chapter 5, asked 2×
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