To re caulk the area around a bathub or shower, you must completely remove the existing caulking. Once you have removed the majority of caulking use a silicone sealer remover to clean off any residual. There is a newer Silicone and Adhesive Remover that is available called Re-mov that doesn't use flammable or corrosive chemicals so itís safe to use on fibreglass and vinyl. Rather than dissolving the silicone this silicone remover breaks the bond with substrate so you can pull off the caulking rather than dissolving it unlike the other silicone removers that have been available; making it easier and less messy to work with. Go to www.removcanada.com for a retailer. Once you have thoroughly cleaned the area, allow it to dry completely before applying the new caulking or you can speed the drying process with a blow dryer.
When you are ready to caulk, fill the tub up to the overflow level and re-seal with a mildew resistant kitchen and bathroom silicone sealant. Leave water in the tub at least twelve hours, this will allow adequate time for the sealant to cure. For a cleaner job, you can use painter's tape along the walls and bathtub edge.
To prevent the black spores from forming around the bathtub, you must control the bathroom moisture and use proper ventilation. The black spores that form in and around a bathtub is caused by a lack of drying in the shower and bath after each usage. A good practice after every shower or bath is to towel the area down and leave the bathroom fan running for at least one hour. Timers or de-humidistats are a great investment for the proper operation of your bathroom fans.