Put 1/2 a cup of borax in a cup or a saucer and use a spray bottle filled with water to wet the borax enough to make a paste. Repeat this step, if necessary.
Scoop up the borax paste with a damp sponge and then scrub the larger areas of the shower. Let the borax paste sit for 10 to 30 minutes.
Use a toothbrush to apply the borax paste to the tighter areas of the shower and then scrub those areas with the toothbrush. Let sit for 10 to 30 minutes.
Use a wet sponge or a handheld shower-head to rinse off the borax paste. Use a squeegee or a dry towel to remove any excess water in the shower.