Getting dependable strength data from concrete on a job site isn't about the tool itself, but about how you use it. The concrete rebound hammer is an excellent instrument, but the numbers it gives are only as good as your technique.
Since the hammer works by measuring the bounce-back from a quick impact, small details in your procedure can significantly change the results. This guide is focused on showing you the correct, professional way to use a concrete rebound hammer, sharing the key practices we've learned that lead to accurate data every time.
But before we jump into the specific step-by-step technique, it’s helpful to first understand the situations where this tool is most valuable. Knowing the problems it solves gives better context for why the proper procedure for how to use a rebound hammer, which we'll cover next, is so important.
Where This Tool Proves Its Worth
We see our clients using these rebound hammers for a wide variety of tasks, which speaks to their practical value. The most common and, from our perspective, most important applications are:
- Checking for consistent quality across a large concrete placement. For example, quickly testing a series of newly cured support columns to ensure they all meet the required strength specification before the next floor is added.
- Performing quality control on new construction to verify the concrete meets design specifications.
- Evaluating the condition of existing infrastructure, like bridges and buildings, which is essential for ongoing structural safety.
- Finding the specific zones in a structure that may have been compromised by fire, frost, or chemical exposure.
- Pinpointing the most strategic locations for taking a core sample. We believe this is one of its smartest uses—ensuring destructive tests are performed only where they are truly needed.
Related article: The Ultimate Guide to an NDT Test for Concrete
How to Use a Concrete Rebound Hammer: A Straightforward Guide
Proper technique is everything if you want numbers you can rely on. A small variation in how you use a rebound hammer can lead to a significant difference in the readings. Here is our more detailed, direct guide for accurate results.
Preparing the Surface
Let's be clear on this – if this step is done poorly, the results will be unreliable. The instrument measures surface hardness, so the surface must be a true representation of the concrete.
Find a spot about the size of your hand. It must be completely clean of any dust, which can cushion the impact, and free of moisture, which can absorb the impact energy and lower the reading.
If the surface is rough or textured, you must use the grinding stone included with the hammer to create a smooth, flat test area. A textured surface has tiny ridges that can fracture on impact, which will always give you a lower, inaccurate number.
Aligning the Hammer
You must hold the instrument perfectly perpendicular to the concrete surface. The impact energy needs to travel straight into the concrete and back out.
If you hold the hammer at an angle, even a slight one, a portion of that energy is lost sideways, resulting in a lower rebound value.
Be consistent with your orientation as well—readings taken horizontally will be slightly different from those taken pointing up or down. Always note your orientation and use the correct conversion chart.
Taking the Reading
Avoid a common mistake: don't 'stab' or 'bang' the hammer against the surface. The correct method when using a concrete rebound hammer is to apply smooth and steady pressure.
As you push, you will feel the internal spring mechanism load. Continue that smooth push until the hammer automatically impacts and gives you a reading. A good test should be a single, fluid motion.
Many modern hammers have a button that freezes the number on the display, a feature we find is extremely helpful for accurate record-keeping.
Read more: How to Read a Rebound Hammer Test: Pro Guide
Determining the Average Value
Never rely on a single reading from one spot. Concrete is not perfectly uniform, so you need an average to get a true picture.
We always tell our clients to take at least 10 to 12 readings in one localized area, each about an inch apart. You will likely get a few readings that are much higher or lower than the rest—discard those outliers.
For example, if your readings are 42, 41, 44, 25, 43, 42, 45, 41, 44, and 43, the reading of 25 is a clear outlier. You would discard it because you likely hit a small air void just below the surface.
Average the remaining nine readings to get your final, trustworthy result. Digital models like our QualiCRH-2000D can even perform this averaging function for you, which saves time on site.
Related article: How to Choose: Mechanical vs Digital Concrete Rebound Hammer
Avoiding Inconsistent Results When You Use a Rebound Hammer
This hammer is an excellent field instrument, but certain things can compromise your readings. In our experience, inconsistent data almost always comes from one of the following factors. Paying close attention to these details is what separates good data from bad.
Surface Irregularities
The hammer is extremely sensitive to the condition of the surface.
A common issue we see is an older, carbonated concrete surface causing artificially high numbers. This is a thin, hardened 'skin' that forms on old concrete and does not reflect the actual strength of the concrete's interior.
As an example, this hardened layer can make a weaker structure appear much stronger than it actually is, which can be dangerously misleading. Always grind away this top layer before testing aged concrete.
The Problem with Rebar
If you take a reading directly over a piece of reinforcing steel, you will get an artificially high number. You are essentially testing the hardness of the steel, not the concrete.
As a guideline, make sure you are testing at least an inch away from any suspected rebar. For critical assessments, we suggest using a simple rebar locator first to map out a safe spot to test.
The Concrete Mix Itself
The type of aggregate and cement used in the mix will influence the final numbers, sometimes significantly.
A concrete made with a softer aggregate like limestone will give different rebound values than a concrete made with hard granite, even if their compressive strengths are identical.
For critical projects, you should develop a unique correlation chart by comparing your hammer’s readings to the results from a lab-tested core sample of the same mix.
Operator Consistency
So much of this comes down to the person using the tool. If your results are erratic, it’s often due to an inconsistent technique. This can be as simple as the operator getting tired and applying less pressure at the end of the day. The goal is to make every single test a direct replica of the last one. A key part of knowing how to use a rebound hammer correctly is applying the same smooth, consistent pressure every time.
Instrument Calibration
This is a precision tool, not a blunt object. Over time and after thousands of impacts, the internal spring can lose some of its tension, or the mechanism can become dirty, adding friction. Both issues will lead to lower readings. We believe that checking it against a standardized test anvil on a regular basis is non-negotiable for any professional work.
Read more: A Guide to Concrete Rebound Hammer Calibration
Qualitest: For Accurate Rebound Hammer Testing
At Qualitest, we get that you need dependable information from your field tests.
We offer a full range of concrete rebound hammers to suit any need or budget, from our straightforward and durable analog QualiCRH-2000A to the more advanced QualiCRH-2000D digital model. For projects involving high-performance concrete, we also provide specialized High Strength Concrete Rebound Hammers.
Our cost-effective products are made to handle the demands of a real job site and give you the information you need to make sound decisions when you use a concrete rebound hammer.
Whether you’re in charge of quality control on a new project or are assessing the condition of an existing asset, one of our concrete rebound hammers is the right tool for the job. Look through the options on our site or contact us directly to see how we can support your testing needs.
