Theoretically, there is no reason for grout under a baseplate. Theoretically, the concrete would be perfectly flat, dead-nuts level left and right and fore-and-aft (or north-south-east-west for you civil-type readers out there), and the concrete would be clean and dust free machined to a perfectly flat match with the bottom of the plate - which would of course - also be perfectly falt and dead ... More @Wikipedia
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