I’ve had the same issue of mold growing along the bottom horizontal frame of my shower door frame. The upright vertical frame pieces will rarely get spots of mold “under” the thinner areas of caulk (ie. Toward the edges, not in the thicker transition/corner portion of the caulk line). This drove me crazy as the bottom would mold so much faster. Well, obviously it stays wetter, but what makes it mold sooo much more & faster is that there is mold that has penetrated through AND under the caulk and is actually inside the horizontal rail of door frame. Bleaching NEVER really rids the area of mold under this bottom portion of the frame. Even without caulk, theres only a slight crack between the frame and fiberglass tub. I’ve removed caulk from the inside & outside and squirted bleach cleaner under there from both sides as best I could multiple days in a row then recaulked and still mold would grow. THE MOLD IS COMING FROM INSIDE THE RAIL/FRAME/WALL/TILE (whatever) and working it’s way OUT. It’s possible even condensation may be enough moisture for mold. If I figure out a way to ensure not making a mess, I may spray some foam under the frame to see if that stops it.

For someone who is yet to do the project--my concern is water penetration into walls, moreso than the slightly unattractive appearance of cracked grout vs. also sometimes unattractive appearance of caulk. I assume that water can work its way behind cracked grout, yes or no? And water is less likely to get behind a good caulk job, yes or no? Thinking outside the box, I wonder if the following work for a shower.... Wherever the floor meets walls, and perhaps also along the vertical corners of shower wall intersections, CAULK the initial intersections, THEN ADD a piece of tile molding--if can find a close match to the tile--perhaps a "pencil" or a "quarter round" in the vertical corners, perhaps also at floor to wall intersection, or "baseboard" tile placed over the lowest row of wall tile where the floor meets walls) Next, THEN could you use grout to "seal" the edges made by the quarter rounds/and/or baseboard pieces? When that grout cracked, it might not look perfect, but the water still wouldn't get behind the tiles cause the initial intersections have been caulked. Correct or not? Or would you still need to caulk instead of grout those edges? Would love to hear others opinions on this idea, especially Bill V. (I am NOT an expert by any means on this stuff). Lainie

DAP makes ALEX in several different formulas: ALEX PAINTER'S CAULK - (white only) acrylic latex - 25 yr. ALEX FAST DRY - (white only) 40 min. drying - 35 yr. ALEX PLUS - (clear & colors) acrylic latex with silicone - 35 yr. The most flexible and durable caulk/sealant from DAP is DYNAFLEX 230 but it is known to have a problem with mildew so don't use it in wet or damp areas. DAP's answer to that problem appears to be ULTRA 230 PREMIUM with Microban. Both have a 50 yr. satisfaction guarantee and cost considerably more. I would avoid the clear DAP caulks that turn white because they have a reputation for shrinking excessively and require more time before painting.

Any grout between the tile and tub should be removed so pull it out with the old sealant and re seal the joint with the most expensive 100% silicone sealant you can find, not just tile and tub caulk. It is necessary to thoroughly remove all of the original silicone in order for the new silicone to stick. Unfortunately that is extremely difficult. Here are some suggestions from GE: "It is VERY difficult to remove silicone from a surface. However, if you must remove it, follow the suggestions below. To remove silicone sealant from surfaces, first remove as much as possible by cutting/peeling/scraping excess sealant from surface. * For ceramic tile, marble, Formica, fiberglass, etc., use 100% mineral spirits (turpentine) and a non-abrasive scouring pad. Test solvent on a hidden area of the surface to ensure that discoloration will not occur. If discoloration does occur, contact the manufacturer of the surface for further assistance. * For glass surfaces, use a razor blade to remove as much as possible, then apply mineral spirits. Remove excess as much as possible, then apply mineral spirits. Remove excess with a towel or other suitable cleaning utensil that will not mar the surface (such as a non-abrasive pad). NOTE: For surfaces such as hard plastics or painted surfaces, including cars, use rubbing alcohol and a soft cloth. Do not use mineral spirits. Only use these solvents in a well-ventilated area and follow all safety precautions and instructions listed on the product label. Material Safety Data Sheets for GE Sealants & Adhesives products are available upon request. Similar information for solvents and other chemicals you choose to use with GE products should be obtained from your suppliers. When solvents are used, proper safety precautions must be observed. On Rough, Porous Surfaces: To remove sealant from a porous/rough surface, (concrete, brick, wallpaper) remove as much of the sealant as possible (same as smooth surface). If necessary, use a wire brush in conjunction with mineral spirits. NOTE: We do not recommend use of a wire brush to remove sealant from wood surfaces, as doing so could damage the wood. Also, mineral spirits should not be used if the wood has any type of finish on it. Test solvent on a hidden area before applying. Mineral spirits are flammable and should be used away from sparks, flames and other sources of ignition. Only use these solvents in a well-ventilated area and follow all safety precautions and instructions listed on the product label. Material Safety Data Sheets for GE Sealants & Adhesives products are available upon request. Similar information for solvents and other chemicals you choose to use with GE products should be obtained from your suppliers. When solvents are used, proper safety precautions must be observed. NOTE: There is nothing that will dissolve silicone. NOTE: If reapplying silicone to the area, remove the old sealant. Then clean the area with a disinfectant if mold or mildew is present, apply rubbing alcohol. Let the area dry before re-applying silicone. Do not use soap to clean surfaces to be sealed because silicone will not adhere to surfaces covered with any soap scum." I suspect this is a far more difficult job than you yet realize.