What is the recommended grout for repairing a millstone?  The  millstone, 
early 19th century, has a rough 1" by 8" section that has broken  off an 
outside edge.  All pieces of the fine-grained sandstone are  available for 
mending.  Once repaired, the millstone will be installed in a  park as a 
landscape feature.  Although it will not be subject to weight  and/or pressure, it 
will be exposed to the extremes of a cold-weather  climate.
Thanks,
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