The Top 14 Boat Mold Removal Techniques

So you think you’re going to sail off into the sunset enjoying 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 listing the 14 top mold removal techniques, please allow me to provide a bit of 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 terribly musty and rank but also it can 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 off as one spore and then grows and spreads. Mold comes in all sorts of colors – black, blue, yellow, brow, white and gray.

What is mildew?

Mildew is a form of mold that looks like a thin dusting of black, grey, yellow or white powder that appears on fabric, upholstery and walls. Mildew on boats seems to appear overnight. From time to time 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 surfaces that are damp for extended periods or where dirt is allowed to accumulate.

With warmth and high humidity mold grows quickly and once it’s formed it can survive for years. Mold also grows in cold climates. And unfortunately freezing temperatures don’t kill mold as the spores are resistant to drying out. If temperatures go up 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 that it is to stop it. A boat owners three main priorities to prevent 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 priorities what’s important versus what’s not. 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.

Obviously, 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 towel to find the stream and consider pouring buckets of colored water over the boat (use food color) to get a better visual.


Leaks that are left unattended will turn into a serious 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. And with water, air and hull temperatures changing at different rates, condensation forms. Add people living on board and there’s even a higher chance for moisture.

There are a couple major actions a boat owner can take to prevent damp. You can either use a dehumidifier and/or maximize ventilation.

A dehumidifier reduces the level of humidity 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 boats 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 take the moisture out of the air within the boat to reduce the likelihood of damp.

The other major action you can take to minimize damp 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. It’s imperative that the air is moving through the boat. Ideally, you want the air inside the boat to be replaced at least every hour. Ventilation systems can be installed that pull air in and exhaust air out. Alternatively, fans can be used to move air around provided the ventilation system is allowing air in and out of the boat.

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

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

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

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 want it sitting around. If you have a shower curtain, open it up so it’s not folded against itself preventing air to dry 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 super dry before folding and storing.

Do weekly 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 teak tends to bow up rather than create a small valley between each plank of teak. When this happens 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

If you’re proactive and fix leaks instantly in addition to keeping a routine of either drying the moisture or circulating the air in AND keeping a clean boat, you’ll drastically reduce your incidents of mold and mildew.

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

Boat mold removal in general…

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 your white sheets, but it could ruin your headlining’s, 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. Make sure the boat is very well ventilated and children and pets are not around. Or, better yet, use a natural and less expensive mold and mildew killer… (read on)

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 a 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 – In addition to 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 and then 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 then spray the mixture onto hard surfaces where mold and mildew are apparent. Let the solution do it’s 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 to prevent future growth. Remember to always shake the mixture before you spray as oil and water separate.

6. Grapefruit seed extract essential oil also works well. Follow the same 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 a half-cup to one cup of borax to a gallon of water. Spray or wipe on the surface and wipe away the mold. Spray solution again on the surface and let dry.

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

9. Boat mold removal on the deck

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

If your boat has a teak deck, consider treating it with Borocal at least once a season for mold prevention. Boracol is a chemical that can be used on wood for the management of mold, fungal growth, mildew, slime, dry rot and insect attack.

To get step-by-step instructions and a video on how to use Boracol on a teak deck read Teak Deck Maintenance Using Boracol.

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.

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

On our wood and headlining’s I always use vinegar and water. It’s easy, vinegar is very inexpensive, there’s no chemicals and it works! The smell of vinegar is annoying for an hour or two but it doesn’t take long for it to disappear. Between cleaning with vinegar I use a wood polish to add life back into the wood.

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.

What many people fail to remember is that mold and mildew has 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 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 might then want to run some fresh solution through one last time.

13. Boat mold removal in closets

Ultimately, if you are able to do so, 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.

If you are on the boat, however, you can purchase chemical dehumidifiers to put in closets prone to moisture. The following DampRid product can be used for larger areas but there are also smaller products good for closets. Aside from Amazon, these dehumidifiers can be found at large hardware/lumber stores.

14. Boat mold removal in items kept in storage

Every autumn I take my summer clothes 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 moister and mold stays out. From time to time I’ve had the unfortunate situation 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. And in each bag I add a 30gram ‘Dry & Dry’ Silica Gel Desiccant sachet (see below – I order these from Amazon).

Anything else about mold and mildew – Frequently Asked Questions

Question: Is it worthwhile to run a dehumidifier while living on the boat during cooler seasons?

My experience is that running a dehumidifier while living on the boat (with the boat closed up) doesn’t work very 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 within 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 to go out for the day we open as many windows as possible. We also have fans going 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 boat on the hard for a season, return to the boat and it’s filled with fungus. It’s a terrible, terrible tragedy that happens all the time. Considering the high rate of mold/mildew issues, and the extensive cost of fixing them, insurance companies just won’t cover the damages.

Question: What can I do when laying the boat up for the season in addition to 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.

Would you like even more valuable ‘how-to’ information?

If you like the straight-to-the-point easy-to-use information that I provide, consider purchasing one or all of my sailing/sailboat guides. My aim is to make it easier to get out sailing. The industry is full of disingenuous marine sales people eager to take money from newbies…salty sea dogs make ‘youngsters’ (aged 20 to 70) feel awkward because they don’t know a particular sailing term…and sailing books are full of complicated equations, charts and explanations.

I make things simple. I help readers to avoid being conned, feeling awkward and/or wasting time! And…I write about ways for you to make it easier to get out sailing. Enough said – check out my sailing guides now.