repair cracked grout in shower

I noticed that the grout on the shower floor at the edge and corner started to crack. The contractor who did the work (for previous owner) should have caulked the edge and corner.
I am thinking of taking out the grout and caulk them. But I noticed that some of the gaps are almost 1/2 inch wide. I am not sure if caulk (e.g. silicone II) can seal this large gap.
Is it okay to use silicone caulk for gaps as large as 1/2 inch? If not, what can I do?
Thanks
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argh. remove all that crap grout and re-grout it. caulk ?
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snipped-for-privacy@hotmail.com wrote:

Applied properly caulk can fill a gap as wide as 1/2 mile. The main tools in your box should be a hammer, duct tape, caulk and a screwdriver.
Whenever tile changes direction or meets another material I apply caulk. If you have cracks in the middle, you should regrout. Good luck matching the color!
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