On Thursday, 30 June 2016 14:00:05 UTC+1, Adam Funk wrote:
I've been working on tidying up the grout in the shower by applying
thick bleach with a paintbrush, leaving it for a while, then rinsing
it off. I'm wondering --- would it be more effective if I made it
even thicker so it stayed in place better, & what is a good way to do
that?

A dose of thin bleach shoud do the job. if your house is damp you need better ventilation and a more frequent application. If it is very damp, move.