Whether you are looking to go into construction as a career or you are doing some DIY concrete work around the house, something you need to know all about is rebar. When it comes to working with existing concrete structures, something you need to be able to do is find the rebar inside of it.
Why is it Important to Know Where Rebar is?
One of the main reasons why it is so important to know where rebar is located is because you might want to drill into the concrete. If you are building some sort of foundation or structure with walls, out of concrete, you will need to drill into the concrete in order to build vertically.
However, if you happen to drill right into the rebar, for one, you will break your concrete drill, and moreover, you won’t be able to drill down further, and therefore won’t be able to go as deep as is required for the task at hand.
Next, if you are looking to use a concrete saw to alter or remove parts of the concrete slab or structure, although a concrete saw can make quick work out of concrete, if that fast-spinning blade hits rebar, you will be in serious trouble. For one, the saw just won’t be able to make it through the rebar, and this would therefore be a waste of time.
Yet, the real issue occurs when saw blades hit rebar, crack and break, and potentially eject deadly shrapnel in your direction.
Simply put, whether you are drilling or sawing through concrete if either your drill or saw hit the rebar, you will be in serious trouble.
Finally, if you are planning to build vertically on top of concrete, knowing where the rebar is located is essential to the overall structural integrity of the final project. If there is rebar missing from certain areas within the concrete, building on top of it can be hazardous, or at the very least, it can lead to structural integrity issues.
Whatever the case may be, knowing where rebar is located within concrete is very important.
The Two Best Ways to Find Rebar in Concrete
When it comes down to it, there are two main methods at your disposal to locate rebar inside the concrete. You can either use a handheld rebar locator or a special radar unit known as GPR or ground-penetrating radar.
Back in the day, contractors would use cumbersome X-ray machines to find rebar, which is still technically an option at your disposal, although the technology is quite outdated and the machines are huge.
With that out of the way, let’s take a look at the two modern methods for locating rebar.
Method #1: Using a Handheld Rebar Locator
You can go to a concrete surveying company and rent a small handheld rebar locator. You do need to make sure that the unit in question is designed for locating metal rebar, or else it will not work. These units look like stud finders and can usually detect rebar down to 8 inches below the surface of the concrete.
Here is how to use a rebar locator:
- Hold the rebar locator so that it is flat against the surface of the concrete, and start along the edge of the concrete so that the handle of the unit points down.
- Press the power button and wait for the display to turn on.
- If the concrete is very rough or coarse, place a thin piece of cardboard in between the concrete and the locator.
- Slide the locator horizontally along the concrete until it beeps, which is an indication that it has found rebar. Some locators feature + and – signs, with the plus sign meaning that you are moving the locator closer to the rebar, and vice versa.
- When the locator beeps, use some chalk or any other marking utensil to mark the location of the rebar in the concrete.
- The display will indicate the depth of the rebar. Write this down, either on paper or right on the concrete. Keep in mind that these units give you an approximate location of the rebar, but not the exact depth.
- Continue moving the locator horizontally to locate all rebar bars, and then repeat the process, but instead of moving horizontally, move vertically to find all of the crossbars. If the machine does not beep at all, either there is no rebar at all, or the rebar is too deep for it to detect.
Method #2: Using a Concrete Radar
Concrete radars are larger and more advanced versions of the smaller handheld units. They are far more powerful and can locate rebar far deeper in concrete than the handheld units. They cost at least around 1,000 dollars to buy. That said, you can rent one as well.
Here is how to use a concrete radar, also known as a GPR:
- Place the cart on the edge of the concrete and power it up. It is a good idea to start in the bottom right corner.
- Start by pushing the cart horizontally and wait until the display fills up. You will see a chart on the display. Keep moving the unit until you get to the other side of the concrete or until the chart on the display is full. Keep in mind that if you keep moving the cart once the display chart is full, information from the beginning of the scan will probably be lost.
- Now, move the cart back in the same direction from where you started, so back to the start point. On the display, you will see curves with points at the top, and you will see a vertical dotted line. As you move the cart back over the path you just scanned, once the vertical line matches up with the top point of a curve, that is where the rebar is located.
- Use the display’s guide, ruler, or other measuring unit to determine the depth of the rebar, and then write it down. Most GPR units should also have small lasers that come out of each side. These indicate the exact location of the rebar in the concrete. Use chalk to make markings where the laser is.
- Continue this process of moving the GPR unit horizontally along the concrete. Each time one row is down, move up by 6 to 8 inches. Once you have completed finding the horizontal bars, repeat the whole process again, but instead of moving horizontally, move vertically in order to find the crossbars.
A Third, Alternative Way: Using a Simple Metal Detector
Another method at your disposal is to use a simple metal detector, such as those that people use at the beach to find buried treasure in the sand. All you have to do is turn the metal detector on, and if you have an advanced unit, you may even be able to set the scanning depth.
Simply pass the metal detector over the concrete, and when it beeps (or the display flashes), the detector has found metal, which in this case should be rebar. Use chalk or some other marking utensil to mark the location of the rebar.
To ensure that you have found a full bar, run the metal detector along the horizontal or vertical plane. If it keeps beeping as you move it in a line, you have located rebar.
Beware that metal detectors are not overly accurate, so they may not provide you with an exact location and depth, although they will give you an idea of where the rebar is located, a general area. We would recommend using the handheld rebar locator or the GPR unit as opposed to a metal detector, though.
Will a Stud Finder Find Rebar in Concrete?
For the most part, no, stud finders cannot locate rebar in concrete. Most stud finders are designed to locate wooden studs behind wooden, plaster, or sheetrock walls. With that, generally speaking, they are not powerful enough to send the signal through concrete.
Now, there are special multi-purpose units out there that can be used as both stud finders and rebar locators, but to answer the question, no a normal stud finder designed for wood will not work to find rebar in concrete.
The bottom line is that if you want to find rebar in concrete, you could use a metal detector, although the accuracy is questionable, or you could use a heavy and cumbersome Xray machine too.
However, the best way to find rebar in concrete is by using a small handheld rebar locator or a larger GPR unit. Either of these two tools will provide you not only with the most accurate results but will also be the easiest to use.