I installed 12" wall and floor tiles in a bathroom with 2"x2" tiles on
what used to be a painted, concrete shower floor with a 6" stub wall
about six months ago. It's all holding up nicely but I did find
recently, some missing grout where the 2" tile meets the schluder
which supports the bottom of the 12" tile as it goes up the wall. Gaps
were approximately 1/4" or less and I used a fine brush wire wheel in
a drill to clean off any soap scum or old grout sealant prior to
re-grouting. The grout repair *seems* to have gone well and now my 3
days (or so) are running where I mist the grout a couple of times a
day to get some cure time prior to using the shower again. Here's the
big question... Instead of using a conventional grout sealer, should I
use clear silicone or tub caulk? They make some supposed 50 year stuff
now and in my experience with it, it seems more effective than what my
experience with the grout sealer was (kind of a cheezy bottle with a
brush end used to dab the grout lines). The grout was a sanded
portland cement grout (though now in retrospect, I wonder if I should
have used an epoxy since it's a shower floor). Anyway, just trying to
protect the investment with whatever I can get in there with to
protect existing grout lines. The integrity of the grout appears to be
holding well - just wondering about a longer term sealant for it.

2nd question as a quickie... what is the preferred method of cleaning
grout lines prior to re-sealing? The wire brush *seemed* pretty
effective but not being an expert, there might be something that works
better. TIA for any help. :-)