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diamondtiling
This is an interesting debate, as i know a few guys that do site work and they always grout the internals and Silicon over the top. The Mastic Man i know insists on it, as you get a better finish with the Silicon (although it clearly isn't doing its job!?!?!). This is on residential properties; the only time they leave proper expansion gaps is on large commercial jobs.
I always leave the grout out of internals and where the floor meets the walls in order to Silicon. Anyone who silicones over grout is making a mistake and needs to do it properly. It is asking for future problems with expansion issues etc. The whole point of not grouting these areas is so that the Silicon is pushed into the joint to gain purchase on the tiles, its not just for cosmetic reasons.