The reason grout is used in machine base foundations is to mate the relatively bumpy concrete surface to the relatively smooth steel foot pad under-surface. If you just put the foot pads on concrete, it would only bear on the highest spots in the concrete creating stress concentrations in both the concrete and on the foot pad. The grout will do very little in the way of damping vibration, however. You'll need some base isolators between the foot pad and another foot pad mounted on the grout.

http://www.efunda.com/forum/show_message.cfm?start=1&thread=...


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Note added at 4 hrs (2012-01-22 14:07:35 GMT)
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Top of rough concrete (under grout)

http://www.mybrcc.edu/bid_files/Specifications/0430.1 - Conc...


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Note added at 6 hrs (2012-01-22 16:03:38 GMT)
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The more evenly balanced and smooth running the machine, the less unbalanced forces there are which must be transmitted from the machine, through the grout and into the foundation. An understanding of this function points out the importance of a good grout and anchor bolt system to join the machine to the concrete block. Excessive vibration is often a symptom of a problem in one of the links in the attachment system. It also can be from an abnormal machinery operating condition, where the unbalanced forces have increased beyond normal operating forces.

http://www.mdt-quadrant2.com.my/index.php?option=com_content...