clipped

http://www.prosourcecenter.com/catalog/10090GroutSaw.jpg


Are you sure about this .... "add clean grout on top of the old" ? It
just doesn't sound right to me. And I would think it would just be
easier to remove all the old grout but this isn't a fun job either.

I don't know of an easy option. Removing some of the old grout....I
think removing 1/8" depth is minimum to give new grout a secure bed...is
the only way to renew it. Unless you try sandpaper and then resealing.
I removed and replaced grout in a tile shower stall that had 1x4 tiles
and fine grout lines. Hard work with a Dremel grout tool, but doable
(and I'm an old lady). Most difficult were getting down to do the
lowest portions and then putting in new grout; it takes some muscle to
mush in the new grout.