The Top 14 Boat Mold Removal Techniques

So you think you’ll sail off into the sunset, enjoying the fresh air and feeling amazingly healthy? Not if you have mold on board…and every boat has mold. The good news, however, is that there are actions you can take to prevent the spread of mold and several techniques for boat mold removal.

Before we move onto boat mold removal techniques, if you’re tired of being reactive regarding boat problems, get a copy of my guide, Checklists For Sailors: Passage Planning, Sailboat Maintenance, Cleaning, Medical, & More!

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Before listing the 14 top mold removal techniques, please allow me to provide some background on mold and mildew so you understand what it is, how it forms, how best to prevent it, and ultimately, how to remove it when you find it.

What is mold?

Mold is a fungus that wreaks havoc aboard boats. Eventually, every boat owner becomes a boat mold removal expert. Not only can mold make a boat smell musty and rank, but it can also create significant health problems. The most common health issues include respiratory problems, allergic reactions, migraines, inflammation and pain in the joints, mental deficiencies, and extreme fatigue.

Mold often looks furry and is circular. It starts as one spore and then grows and spreads. Mold comes in all sorts of colors—black, blue, yellow, brown, white, and gray.

What is mildew?

Mildew is a mold that appears on fabric, upholstery, and walls as a thin dusting of black, grey, yellow, or white powder. It seems to appear overnight on boats. Occasionally, we’ve had our whole galley coated with what looks like a light dust…It’s disgusting.

How are mold and mildew formed?

Mold and mildew grow on damp surfaces for extended periods or where dirt can accumulate.

With warmth and high humidity, mold multiplies; once formed, it can survive for years. Mold also grows in cold climates. Unfortunately, freezing temperatures don’t kill mold, as the spores are resistant to drying out. If temperatures increase after a freeze, mold spores will reactivate and grow.

Boat mold removal techniques are important…

…but eliminating the conditions that allow mold to grow is the key!

Ultimately, it’s easier to prevent mold from growing than it is to stop it. A boat owner’s three main priorities to avoid mold and mildew are as follows:

1. Fix any leaks the second you discover them

Considering that there’s always a servicing/maintenance ‘to-do’ list on a boat, it can often be difficult to prioritize what’s important versus what’s not. See my Sailboat Maintenance Checklist. When it comes to leaks, they are ALWAYS important. A leak that’s left untended can quickly turn your boat into a stinking, unhealthy environment.

If your boat is sinking, it’s best to deal with that issue, but stopping leaks is not something to avoid. Don’t put your head in the sand if you can’t figure out the source of the leak. Keep looking. Make trails of paper towels to find the stream, and consider pouring buckets of colored water over the boat (use food coloring) to get a better visual.

Leaks left unattended can become a severe mold fest, and you will regret not fixing them sooner…

2. Prevent mold by reducing the likelihood of damp conditions

Mold thrives when boats are closed up. Air that is trapped inside holds moisture that can’t escape—condensation forms with water, air, and hull temperatures changing at different rates. Add people living on board, and there’s an even higher chance of moisture.

A boat owner can take a couple of significant actions to prevent dampness. You can either use a dehumidifier and/or maximize ventilation.

A dehumidifier reduces the humidity level in the air, allowing the boat to dry out.

Dehumidifiers work well when a boat is sealed up and left unattended. Many boat owners reduce humidity by using the boat air-conditioning system (many have a dehumidifier setting), or you can set up a stand-alone dehumidifier in the galley sink or place one in the bilge so that the water run-off can exit the boat.

The key with dehumidifiers is that the boat must be well sealed. The objective is to remove moisture from the air within the boat to reduce the likelihood of damp.

The other significant action you can take to minimize dampness is to make sure the air within the boat is circulated.

This can be done by ensuring the boat is well-ventilated in addition to having electric vents, or fans move the air around.

Generally, a standard ventilation system won’t be enough to keep mold at bay. The air must be moving through the boat. Ideally, you want the air inside the ship to be replaced at least every hour. Ventilation systems can be installed that pull air in and exhaust air out. Alternatively, fans can move air around, provided the ventilation system allows air in and out of the boat.

The ultimate aim, therefore, is to remove the moisture in the air or constantly circulate the air so that the possibility of dampness is eliminated.

This leads us to the third main priority to prevent mold and mildew…

3. Clean up dirt, spills, and crumbs and immediately wash any seawater that touches the canvas, soft furnishings, etc., with fresh water.

Mold and mildew grow on dirty surfaces. When something gets dirty, you’ll want to clean it up. When something gets wet with salt water, you’ll want to wash it off with fresh water. Salt keeps things damp. And even with fresh water, you don’t like it sitting around. If you have a shower curtain, open it up so it’s not folded against itself, preventing air from drying it. After a shower in the head, make sure the window is open to allow the air to circulate. When doing laundry, ensure that items are dry before folding and storing.

On a weekly basis, complete spot checks looking for mold and mildew. Problem areas include:

• Portlights and hatches
• Leak spots (if you don’t fix them…)
• Loose stanchions
• Chain plates that penetrate the deck
• Deck-stepped masts
• Water leaking though the deck core – big issue as it can rot the decks core
• Clogged cockpit scuppers – if these get clogged water can overflow and run into areas it’s shouldn’t be
• Teak deck filler that bubbles up rather than down…Over time, the black filler on the teak tends to bow up rather than create a small valley between each teak plank. When this happens, it’s important to do a teak deck repair – you can take a long, flexible box knife, slightly bend it, and carve a valley back in the teak filler. It’s a painstaking job but it allows water to sit in the filler rather than on the teak wood)
• Places where snow can accumulate
• Closets (whenever possible open all your closets to let air circulate in them and never pack them too full)
• Hatch roller blinds (make sure to periodically spray with a anti fungal solution)
• Behind curtains (up at the top where condensation can form – see picture below as this is what mold can look like when you remove curtains)
• Inside ventilation systems

Suppose you’re proactive and fix leaks instantly, in addition to keeping a routine of drying the moisture or circulating the air in AND keeping a clean boat. In that case, you’ll drastically reduce your incidents of mold and mildew. Discover checklists that will allow you to be proactive about all your boating needs. Get Checklists for Sailors.

But what do you do when you find mold or mildew?

With any mold and mildew solution, always spot-test the afflicted area first to ensure you don’t damage it with the solution you’ve decided to use. Some cleaning solutions may work well on one surface yet destroy another. Bleach is an example of a solution you’ll want to be careful with.

Bleach might work very well in a fridge, countertop, or with white sheets, but it could ruin your headlining, soft furnishings, and wood.

If you’re unsure as to whether the solution will damage a surface do a small little patch that’s preferably hidden.

The 15 Top boat mold removal techniques

1. Use store-bought cleaning solutions dedicated to mold and mildew removal – use as per directions on the bottle. Be careful when using chemicals on a boat. Ensure the vessel is well-ventilated and children and pets are not around. Or, better yet, use a natural and less expensive mold and mildew killer (keep reading). The product below works well. It gets rid of mildew without any scrubbing.

2. 3% Hydrogen peroxide solution (diluted to one part hydrogen and three parts water) – Hydrogen peroxide is anti-fungal, anti-viral, and anti-bacterial. Talk about killing three birds with one stone! Apply generously with a damp cloth or spray bottle and leave to soak for a while. Wash off with light, soapy water, and a soft-bristled brush if necessary. Caution: Hydrogen peroxide can act like a bleach on delicate surfaces.

3. Diluted vinegar—Use three parts white vinegar and two parts water. For very bad cases of mold/mildew, you can use undiluted vinegar. Add to a spray bottle or use a sponge to cover surfaces. Let it sit for a while to allow the vinegar to kill the mold. Wash with warm water and then consider lightly spraying the surface again to prevent more growth. Leave to dry.

4. Baking soda – Besides killing mold, baking soda absorbs moisture and keeps mold away. Add ¼ tablespoon of baking soda to a spray bottle full of water and shake. Spray the surface and then use a sponge or soft brush to remove the mold. Rinse the surface with water, spray again, and let the surface dry.

5. Tea Tree oil – this natural essential oil is a powerful natural mold killer; it’s a fungicide. To use this essential oil to kill existing mold and mildew, add ten drops of tea tree oil to one cup of water in a glass spray bottle. Oils don’t react well to plastic; therefore, a glass spray bottle is preferred. Shake and spray the mixture onto hard surfaces where mold and mildew are apparent. Let the solution do its magic. Use a sponge or soft brush to remove the mold. Spray with the solution and let dry. With repeated use, this all-natural cleaner will kill the mold/mildew and help prevent future growth. Always shake the mixture before spraying it as oil and water separate.

6. Grapefruit seed extract essential oil also works well. Follow the exact instructions as noted with Tea Tree Oil.

7. Diluted bleach – Dilute it with three parts water. Use a spray bottle to spray, wipe the mold off, and then wash with water.

8. Borax—Add half a cup to one cup of borax to a gallon of water. Spray or wipe the surface and wipe away the mold. Spray the solution again on the surface and let it dry.

And here are some instructions for specific areas around the boat…

9. Boat mold removal on the deck

Always spray off salt water while actively using your boat after a journey. Make sure to spray down the deck, fittings, rigging, sails, mast, hull, and anywhere else salt water may have touched.

If your boat has a teak deck, treat it with Boro-Care at least once a season for mold prevention. Boro-Care is a chemical used on wood to manage mold, fungal growth, mildew, slime, dry rot, and insect attacks. This stuff is amazing!

Read Teak Deck Maintenance Using Boracol, a similar product as Boracare but harder to get, for step-by-step instructions and a video on using Boracol on a teak deck.

Side note: when laying your boat up for a while, it’s common practice to hose the deck down with saltwater. The saltwater will keep the deck damp helping the teak to stay moist.

Below is an old video we made while living in Charleston, South Carolina. We used Borocol then, but now we use Boracare with mold care.

10. Mold removal boat canvas items

Regularly wash away salt and dirt with fresh water. Consider using a specialty canvas mold cleaner, scrubbing gently with a soft brush if necessary. Rinse with fresh water thoroughly. Remember to retreat canvas with water and stain resistance periodically.

With small canvas items like winch covers a solution of equal parts of rubbing alcohol and water can work well. For larger items, consider a borax solution.

11. Boat mold removal on internal wood

I always use vinegar and water to clean our wood and headlining. Vinegar is very inexpensive, there are no chemicals, and it works! The smell of vinegar is annoying for an hour or two, but it doesn’t take long to disappear. Between cleaning with vinegar, I use a wood polish to add life to the vine wood. It’s easy. Make sure to read my Top 15 Sailing Maintenance Tips.

12. Mold removal in the galley fridge/freezer

Bleach the inside of the freezer and or use a store bought spray that has both bleach and a mold inhibitor.

Many people need to remember that mold and mildew have a terrible habit of growing in a fridge/freezer drainpipe. Make sure to run a solution through the pipes to clear out any mold that has formed. A super chlorination mixture can also be used. Use a cork to plug the drainpipe; if it is not there already, pour the mixture down the pipe and let it sit for a while. After an hour or so, put a 1-gallon or 2-liter plastic jug at the end of the drain pipe and pull the plug. You should run some fresh solutions through one last time.

13. Boat mold removal in closets

If you can, keep your closets open so air can circulate. If you’re not using the boat, remove any bedding, towels, or fabric items, as these tend to collect moisture.

However, if you are on the boat, you can purchase chemical dehumidifiers in closets prone to moisture. The following DampRid products can be used for larger areas, but smaller products are also suitable for closets. Aside from Amazon, these dehumidifiers can be found at large hardware/lumber stores. We’ve used them for years and have never been disappointed.

14. Boat mold removal in items kept in storage

I take my summer clothes every autumn and put them in a vacuum bag. Once they’re in the bag, I put them in the bilge and pray that the vacuum seal keeps and the moisture and mold stay out. Occasionally, I’ve had unfortunate situations where some of my clothes were ruined beyond repair.

So, what I do now is use smaller vacuum bags so that if one bag goes, it’s not a total disaster. I add a 50-gram ‘Dry & Dry’ Silica Gel Desiccant sachet to each bag (see below—I ordered these from Amazon).

Anything else about mold and mildew – Frequently Asked Questions

Question: Is running a dehumidifier while living on the boat during cooler seasons worthwhile?

I experienced that running a dehumidifier while living on the boat (with the boat closed up) doesn’t work well. Entering and exiting the boat allows moisture in. Additionally, living bodies add to the moisture in the air. Even with our dehumidifier running non-stop, we discovered condensation in the boat.

As with everything to do with boats, every situation is different. When one potential solution doesn’t work, try another one.

What we’ve found that works best when living on the boat is to air out the boat as much as possible. If we’re going out for the day, we open as many windows as possible. We also have fans to move the air around. When we’re cooking or boiling water, we always make sure to open a window. Finally, if I ever see condensation on the windows and/or frames around the windows, I wipe it off immediately.

Question: Do insurance policies cover mold and mildew damage?

Usually not! Mold and mildew damage is prolific. Boat owners often put their boats on the hard for a season and return to the boat filled with fungus. It’s a tragedy that happens all the time. Considering the high rate of mold/mildew issues and the extensive cost of fixing them, insurance companies won’t cover the damages.

Question: What can I do when laying the boat up for the season in addition to the things mentioned above?

• Remove all bedding, clothing, towels and other items that can attract moisture
• Reduce the amount of contents in closets and lockers
• Turn up beds to reduce the area under the bed for damp
• Don’t put anything on the beds as moisture can form under an item
• Open all closets – perhaps tie them open so they can’t slam closed if the boat is disturbed (remember that your goal is to have air circulate throughout the whole boat and that includes closets!)
• If you’re going to have your boat shrink wrapped consider:
  • Running a dehumidifier
  • Using specialized solar powered vents designed especially for shrink-wrap
  • Placing chemical dehumidifiers around the boat
• Avoid putting anything on top of beds, sofas and soft furnishings. The area between items can attract moisture.
• Look around the boat and consider how you can ensure moisture is being dried out and/or air is moving all around the boat. Lift some floorboards up so the bilge is getting fresh are too!

What have I missed?

Please leave any comments below on your top boat mold removal techniques.

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