Does this product work on vertical grout or does it need to stand in solution on the grout?
(Elk Grove, CA USA)
In regards to the grout cleaner you recommend.
I have a glass block wall in my shower that needs to have the grout (white) cleaned.
It's not terribly bad just needs to be whitened.
The tiles in the remaining shower have dark brown grout so the product I will use needs to be safe for dark grout.
When cleaning grout on walls, you need to keep the grout wet by spraying the grout every few minutes.
I would keep it wet for about 5-10 minutes before scrubbing with a grout brush.
I don't know why they would change color, the only thing I can think of is mildew.
If it's the mildew remover you are referring to, then you only have to spray it few times and then rinse off after 10 minutes.
No need to keep spraying as it's pretty strong smelling and you don't want to be around after you sprayed it.
If it's the tile and grout cleaner, keep it wet for about 10 minutes.
I hope this information helps.
Good luck with your shower cleaning.