Question: I'd like to know how to clean the mildew from the silicone seals in my frameless shower.
The shower never looks clean with that blackened silicone. Or would I be better off to remove the silicone and settle for a little water leaking out?
Answer: Chlorine bleach removes mildew stains. When the stains are on silicone sealant, one trick is to place wads of toilet tissue against the stained areas and then dampen them with bleach. An old toothbrush works well as a tool for transferring the bleach. Leave the dampened paper in place for half an hour or so, then collect the wads and rinse the shower area.
If there are significant gaps in the sealant, you might want to remove and replace it. Do not just leave the gaps unsealed, however. The biggest challenge is removing all of the old caulk, given that silicone sticks so well. Use a razor scraper with single-edge razors to cut and peel away the silicone and to scrape off any remnants. It helps to use caulk remover. Clean up any residue, using rubbing alcohol to remove residual soap scum.
Spread painter's tape on either side of the seam, with the two pieces spaced just far enough apart to accommodate the widest gap between the two surfaces you are sealing. Cut the tip of the tube of new sealant so it applies a bead no wider than the gap.
The website Family Handyman recommends cutting the tip at an angle of only 20 percent and applying the sealant with the tube at a right angle to the seam, which allows you to complete the whole pass in one motion. That goes a long way toward getting a uniform bead. If you apply the sealant the usual way, at an angle of 45 degrees or so, you run out of working space at the corners and have to interrupt the application.
Immediately smooth the sealant with a damp index finger – one pass only. If it doesn't look perfect and you try to tidy it up by going over it a second time, you will almost certainly make it messier. Remove the tape immediately, or there will be a ridge – a place for mildew to grow – along the edges of the caulk.
Have mineral spirits on hand to clean up smears of silicone caulk. A top-quality caulking gun is also important; the plunger mechanism delivers a more uniform bead than a cheap caulking gun does.