Marine fabricators agree regular cleaning, proper storage and adequate ventilation go a long way toward preventing the unsightliness of mold and mildew, which can form virtually anywhere.

Marine fabricators offer tips for prevention and treatment of mold and mildew.

By Jake Kulju

Mold and mildew can attack any part of a boat, especially damp areas that form between cushions and beneath covers. Nearly all marine fabricators agree: The best way to eradicate mold and mildew is to prevent them before they start. For many boat owners, that is easier said than done. Prevention requires regular cleaning, proper storage and adequate ventilation.

Finding the right foam
Most mold and mildew problems that develop on marine applications are the result of chronic moisture problems. If left untreated, ever-present moisture can create conditions that make it nearly impossible to eradicate mold and mildew. This can lead to fabric staining, unpleasant smells and unsightly discoloration. At the top of the list of usual suspects for moisture retention is seating cushions.

“We used to see a lot of mold and mildew in exterior cushions and exterior seating,” says Chris Costa, owner and president of Costa Marine Canvas in Egg Harbor City, N.J. “We have many ways of preventing that now.”

Costa’s go-to material for mildew prevention in marine cushions is quick-drying foam. “We use Dryfast and EZ Dri brand foams in our exterior cushions,” he says, “including coaming pads in the cockpits of boats or along the gunwales. We want a quick-drying foam that will not act as a sponge when it gets wet, which can create the atmosphere for mold and mildew to grow.”

“I’ll often use Drain Dry reticulated foam,” says Jeff Chase, marine fabricator at Sperry Sails of Marion, Mass. ”If you hold it under a faucet, it lets water run right through. I generally use that kind of foam for exterior cockpit cushions or other exterior seating.”

Sitting water is a breeding ground for mold. Quick-drying foam and mesh cushion bottoms that allow water to “escape” help keep the problem to a minimum.

Making use of mesh
Unfortunately, the right foam isn’t a cure-all. Fabric, especially on cushions, can often sit in water that has passed through them, but has failed to drain completely from the seating structure. Costa anticipates this problem and responds to it by incorporating a mesh on the bottom of his cushions.

“We use mesh on the bottom of our cushions and coaming pads so if any water does get in, the ideas is it will have an escape route through the mesh,” he explains. “We use Textilene and Stamoid brand mesh fabrics. I like them because they allow fabrics to breathe easier and dry faster. The mesh is always on the bottom or a side edge of a cushion in spots where the fabric might snap down to fiberglass or wood.

Ventilation and cleaning
No matter how modern the materials, there is no substitute for proper cleaning and ventilation when it comes to preventing mold and mildew growth.

“You really have to try to decrease the conditions for mold and mildew to form in the first place,” Costa says. “We advise our customers to regularly pick their cushions up and air them out. We’ve pulled cushions off boats that weighed hundreds of pounds because of the water they were holding.”

Costa also points out that poor ventilation can have negative effects on covers and enclosures, as well. “If a bridge is completely enclosed for a long time, we’ll see mold show up,” Costa says. “You have to allow for airflow and ventilation. A lot of times people mistakenly blame a mold problem on their fabric, when in reality, improper ventilation allowed an environment for mold to grow in the first place.”

Greg Smith, marine fabricator at Afton Marina & Yacht Club in Afton, Minn., agrees, stressing the importance of ventilation, especially when a boat is in storage. “Good ventilation during storage helps keep boats dry,” he explains. “Even many of the shrink-wrapped boats have vents put in them to help airflow.”

“Many people do not and will not perform cleaning maintenance on their boats, and that is a huge mistake,” says Master Upholsterer Barry Barber.

Chase shies away altogether from recommending shrink-wrap storage, attributing it to interior mold and mildew build-up. “Shrink-wrap doesn’t breathe, and traps moisture in [a boat’s interior] where water condenses on a warm day and drops all over the boat,” he says. “It’s an incubator for mold and mildew. Even something small like a port light leak can cause dampness when a boat is wrapped up. I don’t recommend shrink-wrap at all, period.”

Chase recommends cotton covers as a suitable alternative. He notes that they are more expensive up front, but they last longer and may end up being cheaper in the long run compared to the cost of regular shrink-wrapping. “The cotton canvas covers are the way to go,” he says, “They breathe well and go much further toward preventing mold and mildew, plus they don’t contribute to the issue of plastic building up in landfills.”

Master Upholsterer Barry Barber of Harbor Custom Canvas in Long Beach, Calif., counts ventilation as a vital step in mold and mildew prevention. “If you’re going to leave your boat for any length of time, unzip your cushions, stand them up, and let them breathe, especially if your boat is in storage,” Barber says. “Simply taking the time to do that can save cushions for years.”

Simply picking up cushions and letting them dry thoroughly will drastically cut down on the conditions that encourage mold and mildew to form.

Costa also emphasizes the importance of regular cleaning. “When people don’t clean their boats it creates conditions for mold and mildew,” he says. “Most of the boats we work on are well-cleaned, but we still see a lot of negligence.”

Chase has an in-house washing facility at his disposal, which illustrates how seriously he regards washing and cleaning. “We do all of our own canvas washing,” he says. “Once many of these fabrics get dirty, they can start to leak and let water leach through to underlying surfaces. The best thing is to keep [your canvas] as clean as you can.”

Smith agrees. “You’ve got to keep your boat clean,” he says. “Mold won’t grow on something that’s clean and dry. I mainly see mold forming on tops that aren’t cared for and cleaned properly.”

Barber notes that failing to clean the top, sides and bottom of all upholstered surfaces can create a breeding ground for undesirable growth. “Many people do not and will not perform cleaning maintenance on their boats, and that is a huge mistake,” he says.

Even sitting in full sunlight, improperly ventilated enclosures can allow mold and mildew to grow rapidly.

Treatment options
Even the best preventive efforts will let the occasional mold or mildew spot occur. When prevention fails, treatment options are available. Costa reaches for Clorox’s outdoor bleach formula, specifically designed for cleaning outdoor furniture. “We suggest using a diluted mixture,” he says, “and suggest testing it on a spot before you clean all of your fabric with it. It is pretty good at killing and removing mold and mildew most of the time.”

Chase also uses bleach products. “We use straight bleach and let it sit for 10 minutes, then thoroughly wash it,” he says. “We also use a non-toxic product called BioShield to help repel water from seams. Water can wick up the threads, causing mildew and mold.”

Barber’s treatment solution of choice is Fabric Guard. “It’s a solution you can spray on your marine fabrics to keep them clean. You can spray it on seams to prevent wicking.”

Mold and mildew might seem like persistent problems for boat owners, but fabricators who work with marine fabrics on a regular basis see where the patterns emerge. It is clear that clean, dry fabrics generally stay mold and mildew free. Before any prevention can occur, however, proper fabrication has to take place, as Barber points out. “You have to do proper fabrication especially when it comes to marine applications,” he says. “When you have an ill-fitting cushion, you create room for moisture.”

Jake Kulju is a freelance writer from Minneapolis, Minn.