If the grout is Portland cement based, and I think it is, it will have all of the drawbacks.
Esentially, if it is pushing on the block enough to cause the iron to distort, who is to say that hasn't caused the iron to fail at those points?
Portland cement bonds well to iron or steel. It does have the tendency to be corrosive at those points though.
Portland cement will also develop expansion cracks, like you see in a sidewalk.
All things considered, I consider it a temporary measure, and the time ticking on each block will vary.
If you are looking for a super trick block, buy a new race block. It has all the correct considerations built into it and is not governed by some kind of Italian stone masons voodoo.
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