How to Vibrate Concrete Properly

Posted On: 06/20/2019 | Posted by: DY Concrete Pumps

Is vibrating concrete necessary? Does vibrating concrete make it stronger? If you’re not sure when to use a concrete vibrator or how to vibrate concrete properly for your construction projects, here is all the information you need.

What Is Concrete Vibrating?

Whenever you pour concrete, tiny air bubbles form. Depending on the mix and the pour, there can be thousands of these air bubbles. The more air bubbles you have in your concrete, the weaker its structural integrity when it hardens. A concrete vibrator is a concrete tool that produces stronger concrete by vigorously shaking the concrete right after you pour it to eliminate the air bubbles or air pockets.

How Does a Concrete Vibrator Work?

There are different types of concrete vibrators that work in different ways. Here are the most common types and a few tips for using them properly:

1. Immersion or Internal Vibrators

Immersion vibrators, also known as internal vibrators, are the most common type of concrete vibrator construction professionals work with. If you are using an internal concrete vibrator, you simply push the vibrator into the wet concrete, then slowly withdraw it as it vibrates the material around it.

Here are a few tips for concrete vibrating with an immersion vibrator:

• Keep the vibrator vertical: As you work, hold the concrete vibrator in an upright position. This orientation lets it work most effectively. Horizontal motion can result in uneven compaction or cause the vibrator to snag on rebar. Be careful not to bend the vibrator — otherwise, it may sustain permanent damage.
• Prevent cold joints: Cold joints develop when insufficient bonding occurs between an old layer of concrete and a new layer. To prevent this issue, be sure to place the tip of the vibrator at least 6 inches into the previous layer of concrete.
• Vibrate with a regular pattern: When you’re using a single internal vibrator, be sure to place it at regular intervals throughout the concrete. Random insertions can result in uneven compaction and air bubble dissolution.
• Stop immediately when compaction is complete: Generally, you’ll know you’ve dissolved all the air bubbles when the concrete surface grows lustrous and air no longer escapes from it. Refrain from vibrating any further — doing so may cause damage.

One last essential tip for immersion vibrators involves what to do when the job is complete. When you’re using an internal vibrator, it is very important to withdraw the device slowly, or you will not get enough vibration to eliminate the majority of its air bubbles. However, you don’t want to leave the vibrator in the concrete too long as it could cause the water to separate from the cement, hurting the look and structural integrity of the concrete.

The solution is to withdraw the vibrator at the rate of about an inch per second. Start by inserting the vibrator head fully, then turning it on and leaving it in place for 10 seconds. Insert it as vertically as possible so it naturally sinks into the concrete. Then remove one inch each second until it is completely withdrawn. If there are still bubbles coming out once you have fully removed the vibrator, repeat the process until no bubbles emerge.

2. Form or Formwork Vibrators

A formwork vibrator, also known as a form vibrator or external vibrator, works with precast concrete. You attach form vibrators to the outside of your concrete form so they can vibrate the air bubbles out.

Here are a few tips for using formwork vibrators:

• Use multiple vibrators: For more extensive pours, you will want to attach several vibrators. That way, you can ensure complete agitation of the concrete and dissolve all air bubbles. Space the vibrators about 6 feet apart for best results.
• Be sure the formwork can vibrate freely: The concrete formwork will need to vibrate sufficiently. Mounting the formwork or mold onto a spring-loaded isolation device helps to ensure unimpeded concrete vibration.
• Submerge the vibrator completely: Always make sure the vibrator heads go all the way into the concrete formwork. Be careful not to turn the vibrators on while parts of the heads remain above the concrete surface.
• Use more vigorous vibration when necessary: Some concrete, known as low-slump concrete, is stiffer and less workable than others. This type of concrete in a formwork will require more vibration for the complete elimination of air bubbles.

3. Surface Vibrators

Surface vibrators, or jumpers, go directly onto the top of your poured concrete. Suitable for concrete slabs 6 inches deep or less, this type of vibrator can give you very smooth surface concrete.

Here are a few tips for vibrating concrete with a surface vibrator:

• Consider complementing with an immersion vibrator: If your concrete is deep and a surface vibrator cannot quite reach the lower layers, use an internal vibrator, as well, for more comprehensive compaction.
• Choose the right vibrator for your application: Surface concrete vibrating equipment comes in several types, including vibrating roller screeds, double- or single-beam screeds and pan-type vibrators. The latter are common in paving work. You’ll want to research different options and choose the type that best suits your work.
• Choose this method when aesthetic appeal is important: Although surface vibrators cannot penetrate very far into concrete, they are ideal for scenarios where you need the concrete to look especially sleek and uniform. Use surface vibrators when you need to create an impressively flat surface.
• Refrain from using vibrators to place the concrete: Use vibrators only to agitate the concrete, never to move it into position. Using surface vibration for positioning can create an uneven surface and a faulty slab overall.

How Long Do You Need to Vibrate Concrete?

The concrete vibrating process typically takes between five to 15 seconds. If there are still bubbles in the concrete when you remove the vibrator, simply repeat the process until there are no bubbles.

Is Vibrating Concrete Necessary?

Vibrating your concrete is almost always recommended since your vibrated concrete will be stronger. But depending on the project, you may have no choice but to vibrate your concrete, as it may be a building code requirement. If you are not planning to vibrate your concrete, you should make sure this will not put you in violation of local building ordinances.

Ordering Concrete Vibrators

If you are looking for a concrete vibrator for your construction project, DY Concrete Pumps can help. We offer reliable Oztec Concrete Vibrators with custom Flexshaft lengths. These concrete vibrators have durable steel heads that produce the highest amplitude and centrifugal force to maximize the radius of influence. To order Oztec concrete vibrators for your project, contact us online now.

-Updated 10/29/2021