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Cleaning and Preventing Mold on Swim Platforms and Seats


Meghan Rice asked:

We have a fiberglass swim platform on the back of our boat. We keep the boat outside and covered when we are not using it. There are black stains on the swim platform. We also have mold on some of the seats. We clean the boat after every use. What would you recommend for those two problems? Thank you!


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Mold and mildew require moisture, food, a constant temperature, calm air and shade or darkness to grow and flourish. If you remove any, or preferably as many as possible of these prerequisites, you will eliminate your mold problem. The other problem is that if left unchecked, mold and mildew will stain the surface and in some cases the stain is indelible and can not be removed. This is especially the case with vinyl seats. Using the right protectors will reduce the chance of permanent damage and make cleaning much easier.

To solve your immediate problems, wash the fiberglass swim platform and with a 1 to 4 solution of Boat Clean Plus and water, using a scrub brush. While still wet, squirt some Boat Scrub on the swim platform and scrub again in all 6 directions. If any stains still remain, mix a 50/50 solution of Boat Clean Plus and Boat Scrub and scrub the areas that are stained until the stain is gone. Rinse well and dry or air dry in the sun. Boat manufacturers use these products to resolve warranty issues.

When the surface is dry, apply 2 coats of Sure Step. This will seal the pores in the gelcoat, leave a protective surface that will resist mold, protect against UV, put a nice shine on the platform and will give you some added traction, especially when the deck is wet. It will also make the swim platform much easier to clean.

To clean the seats, first spray Boat Clean Plus , full strength onto the mold and let stand for 10 to 15 minutes. Wet the seats with water and spray Boat Clean Plus , full strength onto the seats. Scrub the seats with a scrub brush to clean the indentations in the pattern and rinse clean. If stains still remain, scrub these areas with a 50/50 solution of Boat Clean Plus and Boat Scrub , until the stain is removed. If stains still remain, uncover the boat and let the sun get at the seats for a couple of weeks. Sun acts as natural bleach. If the stain still remains then they will have to be recovered. Chlorine bleach, aggressive solvents etc. will remove the stain but ruin the vinyl in the process, so you will have to recover.

When the seats are dry, apply 2 coats of Vinyl Guard. Vinyl Guard is not greasy or slippery and is a double barrier protection system. One part penetrates into the vinyl to restore the plasticizers and make the vinyl feel more luxurious. The second remains on the surface and protects your vinyl against mold staining, UV, suntan oil, food spills and stains. In your area it will last about 3 months before you need to wash with Boat Clean Plus and re-apply.

Now; to the subject of preventing the mold and mildew in the first place. Do not use soap or detergent, not even boat soap to wash your boat. They leave a residue (soap scum) which is food for mold. Think about what happens in showers and bath rooms. Keeping the boat clean is excellent. In future, use Boat Clean Plus , a 1 to 15 or 1 to 20 solution with water to wash your boat. It is free rinsing and will not leave scum for the mold to feed on. At this dilution it will not remove polish or your protectant.

Natural waxes are also food for mold and you should switch to a synthetic, like Premium Boat Shine , Sure Step , VS721 etc. many boat manufacturers now tell their customers not to use Carnauba wax on their boats because of the yellowing and streaking that it causes. Ingredients in sun tan oil or lotion can also be food for mold. Vinyl Guard will prevent mold from getting into the vinyl and is much easier to clean than unprotected vinyl or vinyl with an oil dressing on it.

If you’re in a humid climate, reducing moisture is difficult. Keeping the boat tightly covered makes the problem worst although it is excellent for reducing UV damage. Make sure that the boat can breathe. Either use foam blocks between the top and the boat to allow air circulation or have your top and upholstery shop install vents that allow air but not rain water to enter and circulate. If you have shore power adding a small fan or 100 watt light bulb will reduce the moisture and calm air. If this does not resolve the problem then consider a dehumidifier, either mechanical, or one that uses salt. The salt dehumidifiers remove the moisture but release a corrosive gas that can rust metal and damage other surfaces. The benefit is that they do not need power however, the inside of the boat should be well cleaned as often as possible to remove the corrosive coating.

Controlling temperature and shade are impractical on a boat. Removing the cover will reduce the mold but will create other problems such as fading and oxidation of the gelcoat, which can be worse.

Thanks for your question,

Captain Aurora
Richard Kittar

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