Welcome to the BuildBlock ICF Installer Training Series: Concrete Consolidation. This 20 part video series is intended to be an educational walk through of the ICF building process. From the early planning phases to pouring concrete and finishing walls, this series will provide the basic knowledge you need to have a successful BuildBlock ICF build.
In video number 15 we review the importance of consolidating concrete and the dangers of over vibration.
The videos in this series are produced as a companion to the BuildBlock Installation and Technical Manuals available for free download on the Publications Page or for purchase via the BuildBlock Online Store. You can view more videos in this series via the BuildBlock Blog or by subscribing to the BuildBlock YouTube Page. For a more in depth training experience you can take the free Online ICF Installer Training Series.
In this short video we will review the importance of consolidating concrete as well as the dangers of over-vibrating.
Why is it important to consolidate concrete?
When pouring concrete, air can become trapped inside the concrete mix. If these air pockets aren’t removed they create voids that reduce the strength of the wall. When concrete is poured it sets slightly, this is called slaking.
Vibrating concrete causes it to reverse the initial slake and temporarily returns it to a semi-liquid state. Internally vibrating allows air bubbles to rise as the vibrator is inserted and extracted from the wall.
Internal vibration is required for any ICF structure. External vibration is not sufficient and is not code compliant. Use a low impact pencil vibrator with a ¾ to 1 inch head and a 1.5 HP motor. Either gas or electric is acceptable. The recommended technique is fast in/slow out with an average pull out rate of 4 to 6 inches per second.
ICFs are poured in lifts, each about 4 feet in height, working around the structure adding 4-feet each time until the final wall height is reached. Each concrete lift should be internally vibrated into the lift below it.
The more liquid concrete is, the more pressure it exerts on the ICF blocks. This is why you must be careful not to over vibrate at any point in the process. This is especially important when vibrating above or along the sides of doors and windows. Over vibrating in these areas will cause the block or bucking to lift, slide, buckle, or bulge and could blow out the block.
Additionally, over vibrating in walls can cause large aggregate to settle to the bottom of the wall reducing wall strength as well. These problems are not common, but be aware of potential problems.
Finally before pouring the top course, spot glue every 18 inches, or three webs. This ensures the top course of blocks will not lift when consolidating the last wall lift. Also, when you pour the top course, pour it slightly high since the concrete will settle a little when vibrated.