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The point of the Silicon is three fold: to mask poor cutting in corners, to waterproof holes made after tanking, and to neutralize movement in the surrounding structure.
If you use regular grout in corners where there might be structural movement, and then use Silicon over it, you defeat the purpose of the Silicon, and you risk cracking. Over here, we refer to Silicon as "movement grouting", for just that reason. Use Silicon where it is due, and regular grout where it is due.
Do use Silicon:
-Where the substrate is concrete which is less than one year old (it shrinks)
-Where the substrate is board material, eg drywall, mounted on a wooden or metallic frame (moves with temperature and humidity)
-In new buildings, regardless of substrate, as there will be movement
-Where one substrate material meets another (eg concrete floor meets drywall)
You don't need to use Silicon for structural reasons:
-Where all surfaces are made from concrete which is more than one year old, prefereably more than two years old
There are a few other circumstances where it might, or might not be appropriate, but I can't be arsed. Tell you this though: It's safer to use Silicon, than to not use it. If you think it's needed, from structural reasons or otherwise, then by all means use it.
If you use regular grout in corners where there might be structural movement, and then use Silicon over it, you defeat the purpose of the Silicon, and you risk cracking. Over here, we refer to Silicon as "movement grouting", for just that reason. Use Silicon where it is due, and regular grout where it is due.
Do use Silicon:
-Where the substrate is concrete which is less than one year old (it shrinks)
-Where the substrate is board material, eg drywall, mounted on a wooden or metallic frame (moves with temperature and humidity)
-In new buildings, regardless of substrate, as there will be movement
-Where one substrate material meets another (eg concrete floor meets drywall)
You don't need to use Silicon for structural reasons:
-Where all surfaces are made from concrete which is more than one year old, prefereably more than two years old
There are a few other circumstances where it might, or might not be appropriate, but I can't be arsed. Tell you this though: It's safer to use Silicon, than to not use it. If you think it's needed, from structural reasons or otherwise, then by all means use it.
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