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You rub, buff, polish, and doggedly pursue perfection in your most prized possession, but those mildew-stained caulk lines are laughing at you?
Photo, Lenny Rudow
Difficulty
- Easy
Tools
- Scrub brushes
- Toothbrush
Time
- Varies
Materials
- Boat soap and fresh water
- Soft Scrub with bleach
- Painters tape
- Cotton swabs
- Plastic cup
Cost
- $20
It was a great day of boating, and you’ve just finished a thorough washdown of your pride and joy. She looks great, so you kick back and enjoy a frosty beverage while admiring the glittering gelcoat and shiny stainless steel. Wait a sec, what’s that? Dirty caulk lines are marring your magnificent marine machine?
Most modern boats have caulk around the console or seat bases, running down seams in the gunwales, and ringing the deck hatches. Unfortunately, when your boat’s caulk gets stained or mildewed, a couple of passes with the hose simply won’t do the job. Get down on your hands and knees to scrub and you can get rid of the dirt, but mildew stains remain.
Do those blemishes on your otherwise perfect and pristine boat cause heartache and pain? You bet. But never fear, dear boater, we have the fix.
1. Thoroughly wash the boat with boat soap and a scrub brush. Eliminate as much of the surface contaminants and dirt on the caulk as possible and allow it to dry.
Use a cotton swab to apply a thin layer of Soft Scrub along the caulk line. Photo, Lenny Rudow
3. Dip the cotton swab into the Soft Scrub (if the bottle is low, pour some of the contents into a plastic cup) and apply a thin layer directly to the caulk line. Slowly spin the swab between your fingers as you pull it along to squeeze out the Soft Scrub bit by bit. One dip takes care of 2 to 3 inches of caulk, and one swab is good for 3 to 4 feet before it loses shape. When the cotton begins to come off the swab and/or droops, dripping can become an issue; throw it away and grab a fresh one.
4. Once applied, allow the Soft Scrub to sit for six to eight hours, then thoroughly rinse it away. Most of the caulk should look good, but areas with mildew or deep staining will likely remain. Apply a second coat of Soft Scrub to the problem spots and allow it to sit for at least 12 hours. Very deep staining may require 24 hours to work its magic.
A look at before and after treating the caulk in the gunwale. Those mildew blemishes are gone – woohoo! Photo, Lenny Rudow
In areas with minor staining (like along this console seam) a short-duration application of Soft Scrub worked well. Where mildew stains were present, however, 12 to 24 hours of soak time was necessary. Photo, Lenny Rudow
Tip
Straight bleach will remove staining from caulk but has the potential to do significant damage to just about any surface in short order. Any product that has bleach in it, including gentler ones like Soft Scrub, can dull gelcoat if left on for an extended period.
Sodium hypochlorite is the active ingredient in chlorine bleach. Compare its concentration in the following cleaning products:
- Common household bleach: 5% to 6%
- Tilex: 2.4%
- Soft Scrub: 1.1% If you get any of these products on gelcoat, be sure to rinse it away as soon as possible, but be aware that the stronger the concentration, the more likely damage could occur.
5. Give the boat a thorough wash and rinse. Use a toothbrush to gently scrub along the caulk lines, being careful not to get so aggressive that you pull up any caulk edges. As you scrub, you’ll see some tiny white bits of solidified Soft Scrub get kicked up; be sure to sluice them all away, especially if your boat has foam decking, to prevent staining. Then rinse the entire boat yet again just to be 100% sure no cleaner gets left behind.
Now grab that cold frosty, kick back, and enjoy the epic view of boundless beauty in your fantastically flawless boat.
Popular Advice Tested
As with most boat projects there’s more than one way to skin a cat. While researching this article we tried — and eliminated — two other oft-suggested methods of cleaning the caulk: the Tilex method and the vinegar method.
- THE TILEX METHOD: Many sources on boat maintenance agree that Tilex, a powerful mold and mildew stain remover, works well for removing caulk staining. The advice included taping off the caulk lines to avoid getting Tilex on any other surfaces because it’s quite caustic and can damage many types of finishes. Once the area is saturated, cover with something like plastic wrap for 24 hours before rinsing.
Our results: We began this process, then quickly abandoned it, because in a slight breeze we found it virtually impossible to spray the Tilex without getting it beyond the tape line and onto fiberglass and foam decking material. However, we do note that the small section we completed did, in fact, rinse away clean.
- THE VINEGAR METHOD: We came across the vinegar method on the internet, which, as we all know, is never wrong. The advice is to spray on a 1:1 mix of vinegar and water and scrub the caulk using a toothbrush.
Our results: The section we tested was improved, but only marginally. A second attempt removed some of the remaining staining but plenty of mildew ick was left behind, and we found the results completely unsatisfactory.