Masonry Magazine July 2002 Page. 35
The engineering of the wall
The engineering of the wall can determine the best method of grouting. moment of inertia is carried through that wall a little better. People tend to grout it right to the top of the block and then cut it off. That way, we have a mechanical connection at the same point as the coursing of the block and that's not a good technique.
Consolidate and reconsolidate
CONSOLIDATION OF THE GROUT is required in low-lift as well as high-lift pours. This is accomplished with a lintel head concrete vibrator and doing it is an art form in itself. As Harwell says, "You have to be careful of the head pressures. They can't be allowed to get too high and you can't vibrate it too much if the wall's green because you can blow out the wall-you would blow the mortar joints right out of it. Consolidation is the thing that structural engineers worry about when they specify high-lift grouting."
He continues, "You're supposed to consolidate and then reconsolidate. When grout comes in contact with the block, the block is so porous it absorbs all the excess water. You may start out with a very high water to cement ratio, but after it's in the block and the suction of that block takes that excess water out, you're back down to a water to cement ratio of about .49 or .50. The result is that you get some shrinkage. Cementitious products tend to shrink and that's why you have to do the reconsolidation. Typically it shrinks at that top, not necessarily at the side."
So should you high-lift or low-lift? The right answer is, there is no right answer. Harwell summarizes the dilemma by saying, "The engineering of the wall can determine the best method of grouting. If I have a lot of horizontal bond beams, then I would low-lift, because you can't go any faster than installing your bond beams will allow you. If I am doing a building that has a lot of reinforcing, then I would low-lift simply because I don't have to keep pulling my masons off and sending them to set up on another wall while the grouting team comes in."
He adds, "It never ceases to amaze me that a contractor is getting all this production and then has to stop and go to another wall and wait for the grout crew to come in and grout. If he's low-lift grouting, he can grout right behind the mason. As soon as they get up 4 feet, they just knock it out and keep on going. They can put two laborers with a tub of grout, or a forklift and a laborer and a Grout Hog, and there they go, they never have to stop."
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