Masonry Magazine September 2007 Page. 38
GROUT CONSOLIDATION
and cured, it will probably test low due to the high water-cement ratio," he said. "Grout tested according to ASTM C 1019, sometimes referred to as the 'pin-wheel test,' allows for the highly fluid grout to bleed excess bleed-water into the block, therefore giving a resulting test that reflects the representative strength of grout placed in the wall"
Second, Leonard said, a pre-blended product gives total control to the contractor as to the timing of the grout installation. "When receiving grout via a ready-mix truck, there has to be proper coordination. The truck can come too early or late and grout dispensed in the truck is not as quick of a discharge as other pours. If there is a holdup then demurrage charges can come into play if the wait is excessive," he said.
Further, Leonard advises that grouts should be kept free of contamination. With field mixing, he said, the concern is the contaminates from contact with the earth as the material is dumped on site. In the winter, contaminates, such as salt, should be avoided. "Any contaminate can be detrimental to the ultimate strength of the finished product. Contaminates such as free salts show up in the form of efflorescence and rust shows up as a stain," he said.
The Vibrators
ACCORDING TO the Brick Industry Association, grout in contact with masonry solidifies more rapidly than that in the center of the grout space. It is, therefore, important to consolidate the grout immediately after pouring to completely fill all voids. The
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Consolidation and reconsolidation become more critical as the lift heights increase and the amount of congestion increases in the masonry cores.
best procedure is to have two people performing the operation jointly one to pour the grout and the other to consolidate it. Normally, a mechanical vibrator is employed for this purpose.
Although they're not heavily marketed to mason contractors, mechanical vibrators are the standard tools used to consolidate grout on masonry jobs. A multiplicity of manufacturers build mechanical vibrators and an assortment of attachments designed for multiple applications. Among the leading manufacturers and sellers in the United States are Multiquip Inc. (which also produces the Stow brand of vibrators and other construction equipment), Wacker Construction Equipment (headquartered in Munich, Germany), MBW Inc., Oztec Industries, and Denver Concrete Vibrator. Designs range in size from small, battery-powered units to larger tools such as generator-powered high-cycle vibrators.
A vibrator is used to ensure that the placed grout is even and free of air bubbles so that the material will maintain its strength characteristics. How the vibrators work is by spinning an off-centered weight as much as 10,000 times per minute, forcing any air pockets in the mixture to disperse. Manufacturers note that the head of the vibrator should always be lowered into the pour slowly and pulled out gradually to avoid the formation of an air pocket. The amount of time required to consolidate the grout varies depending on the mix, but it does not usually take more than 30 seconds to settle the grout sufficiently in each section.
Johnathan Cuppett, Multiquip's product manager, said that for mason contractors a flex-shaft vibrator is the most common vibration tool used. The company's MGX Series of flex-shaft vibrators are lightweight, handheld units that provide maximum flexibility by letting the user select from a variety of options best suited to the application, including power source (electric motors or gasoline engines), shaft length (eight options in lengths, from two to 21 feet), and head size (eleven sizes, from 7/8 though 2-3/4 inches in diameter).
Cuppett said that he generally sees two common errors among contractors working with vibrators: over-vibrating and not inserting the vibrator properly into the mixture. If one over-vibrates, he warned, aggregates will settle to the bottom,