- Author: CHENG Concrete
- Difficulty: Moderate
Types of Vibrators:
In this guide we'll demonstrate how to use an electric vibrator, the Vibco US450T. This model requires a controller to limit the speed. Without a controller, plugged straight into an electrical outlet, the vibrator will be operating at full speed. You can control up to 3 table vibrators with the same controller by using an extension chord with a splitter.
For a small countertop, one vibrator will be sufficient. For a longer piece, you'll get better results with multiple vibrators, but you can also move a single vibrator to different locations during the pour.
Even with the right table vibrators, there will still be pinholes in the concrete.
Other techniques include Rodding or using a jig saw with the blade removed to bang on the form.
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Step 1 — Mount the Vibrator and Controller and Secure the form to the casting table ¶
Mount the vibrator with the plate to the casting table with as many 2" long screws as possible (16+). If you use short screws, it will vibrate loose.
Screw the controller to the table and plug in the vibrators. Using a pigtail, you can control up to 3 vibrators with 1 controller.
The form should be secured to the casting table (in this photo the angle iron is holding it to the table). Use 3/4" long screws where the angle iron attaches to the form walls, or you will drill through them.
Test the vibrator before casting to make sure everything works.
Step 2 — Begin Casting ¶
Turn on the table vibrator about half way and begin filling the form with concrete.
If you're using decorative aggregate, the vibration can cause it to bounce out, so keep the vibrator on low speed if that's the case. After the majority of the form is filled, turn the vibrator to full speed.
If you're not using decorative aggregate, fill the form with the vibrator on full speed.
Step 3 — Continue Filling ¶
With the form full, keep the vibrators running for 5+ minutes while you level off the form.
Pat the concrete down to further drive out any air bubbles, making sure any odd-shaped cavities are filled completely.
Step 4 — Smooth the Surface ¶
Use your hands to smooth any air bubbles that are rising to the surface.
At this point you can turn the vibrators off.
Unplug the controller so you don't accidentally turn them on after the concrete starts to set up.
Step 5 — Cover and Cure ¶
After the concrete is poured, cover the piece with plastic while it cures.
This will keep the humidity inside and help prevent the concrete from drying out too quickly.
Any remaining pinholes in the concrete can be filled with slurry. Check out the How-To Slurry Guide for more information.
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