What kind of grout are you using? What kind of loads on the base plate (shear, tension, compression)? Are you looking for minimum thickness or maximum? With flowable epoxy grouts, you can get down to 1/8", maybe even thinned. If you're willing to add some aggregate to cementitious grouts, the sky is the limit, but ask yourself how this impacts your ability to take loads to the foundation.
I am reviewing shop drawings and the contractor is proposing to use 1/2". I'm used to use 2 ~ 3in (1 inch in real light applications), and I thought that was 'strange'.
This is a light application, with a load of +/- 50 kips.
The Contractor's proposing to use Hilti grout. I just did a search and found that Hilti allows for a minimum thickness of 1/2" (10" max., with aggregate) --
So, based on that and on what you're telling me, my Contractor should be Ok!
I usually like to be a little thicker than the minimum, since the grout allowance is going to be used to adjust base plate elevation. Like you said, 1" might be typical to allow for the pier to be cast 1/2" too high. Up to you to determine if that makes sense in this application - for something like a maintenance platform the 1/2" might not matter.
As others have noted, stay within the manufacturer's recommended limits. There are certain flowable grouts that can be placed successfully into very thin layers as canwesteng states.
