Norminn wrote in
m:

Percival P. Cassidy wrote:

For a while after we moved into this house the shower stall looked
fine, but then the grout lines -- especially those between the edge
of the floor and the bottom of the walls -- started looking dirtier
and dirtier.

The usual shower cleaning products did not do much, nor did undiluted
bleach straight from the bottle.

We thought of redoing the shower with plastic or fiberglass panels,
but it's significantly smaller than any standard off-the-shelf units.
No doubt we could get a custom liner made, but probably costing more
than we would be willing to spend.

I've just started attacking the grout with a grout saw, with the
intention of regrouting those joints, but it appears that the
previous owner used silicone caulking compound over the existing
grout along those edges. This complicates cleaning out the crevices.
And even where I've managed to clean out the old grout and caulking
compound, everything is still black, and even straight bleach seems
to have no effect.

Any suggestions about the best way to deal with this?

I regrouted our tiled shower stall with good results, about 4 yrs.
ago. I used the Dremel with special bit and guide. Only tough part
for me was kneeling for the low spots and using enough pressure to
regrout (I'm old ) The black stuff you find is bothersome, and I
hope it is from the previous caulking applied over dirty old grout and
not from a leak that has saturated the wall. If you get through all
of the grout and still find blacfk mold, I've be very concerned that
there is a leak behind the wall. Any chance the original grout was
black? When you get it cleaned out, use full strength bleach, rinse
well, and dry well before you regrout.

I ended up with a few grout joints that didn't fill entirely, which is
due to my lack of muscle and dim lighting. I'd be sure to check the
grout for flaws with light across the joints to catch the little
"misses".

The smallest tip for the Dremel tool is, I believe, 1/8". We have a
few tiles that are apparently closer, and the bit skipped out of the
joint but fortunately did not scratch or chip the tile.

The Dremel "grout" bits are 1/16 or 1/8" There is another general purpose
tapered carbide bit that can be of use as well. Probably others as well.
Still can be time consuming but much less painful than a hand grout saw.