Any DIY experts on here?

[midden]

I wouldn't personally  use only  sealant/silicone because I think the large space is hard to get a good finish. Although that could be my lack of skill.  As fazer says, it shouldn't be over worked and the grout to me keeps some kind of continuity. 

Incidently if you find the silicone quite runny to work with put it in the fridge for half hour