Cleaning Marine Canvas

Sailboat with full cockpit enclosure, including dodger

This sailboat is well protected with a cockpit enclosure, dodger, sail cover, and forward hatch cover.

Most marine canvas covers are made of Sunbrella, a woven acrylic fabric that is water repellent, mildew resistant, and UV resistant. All canvas covers should be cleaned regularly. Salt water leaves behind a residue that holds moisture on the surface, which will result in mildew.

Before you start, first repair any rips or tears in the canvas, and replace any missing grommets or fasteners. See our article on canvas repair for information on repairing your canvas.

Then brush off any loose dirt or soil, then wash with a solution of non-detergent soap and warm water. Avoid detergent-based soaps, as the detergent will damage the finish and make the canvas vulnerable to the elements. Sudbury, Lux and Ivory Soap are good soaps to use, as are liquid dishwashing soaps. Do not allow the soap to dry: Immediately after washing, rinse the canvas thoroughly with cool water to remove all soap residue.

After washing your canvas covers, be sure to dry the canvas thoroughly. (Do not dry your marine canvas in your laundry dryer, however, and never dry clean marine canvas.) Do not fold or store the canvas while it's wet. You can apply a water-repellant coating to the canvas to help keep it in good condition.

Tips on Cleaning and Maintaining Marine Canvas

If the boat cover is acrylic, you will need to re-treat it for water repellence. Check with the manufacturer of the cover for the right solution to use.
Use a clear silicone spray to lubricate the zippers in your marine canvas regularly. Spray the the silicone onto the zipper and work it back and forth into the zipper. Use the same spray to lubricate snaps or other fasteners in the canvas. Avoid using petroleum products, such as Vaseline.
Help prevent the growth of mildew on your canvas covers by spraying them with a solution of 50% white vinegar and 50% water. Keep it in a spray bottle, and spray it on your canvas covers whenever you wash down the boat.
Clean the isinglass in your canvas with a product specifically designed for plastics; do not use any cleaners with ammonia, such as Windex. Rinse all salt and debris from the isinglass first, then dry it with a chamois or soft cloth (not paper towels or any other abrasive material).

You can cover your entire boat, or any part of your boat, with a custom-made marine canvas cover, including outboard engine covers, helm covers, hatch covers, tiller covers, fender covers, sail covers, and more. Every bit of protection you can provide to your boat will help keep it looking and functioning better for the duration of its life. Custom canvas covers may seem expensive, but replacing the canvas every few years is a lot cheaper than repairing and replacing expensive parts of your boat.

More information on caring for marine canvas and isinglass

Waterproofing or Re-Waterproofing Canvas

Conventional cotton canvas typically doesn't need waterproofing; its waterproofing characteristics arise from the way the cotton fibers swell when they get wet. The swollen fibers seal the canvas weave. So classic cotton canvas does fine without any special waterproofing. But cotton canvas isn't used on recreational boats much anymore, as it tends to mildew and can be damaged too easily by bird droppings and similar debris. Most marine canvas today is made of a woven acrylic or vinyl-coated polyester.

The popular Sunbrella canvas, for example, is a tight-weave acrylic. It is breathable, which helps it resist mildew better, and it holds up better under damaging UV rays. It also has better resistance to stains But acrylic canvas needs a special chemical treatment to give it the needed water repellancy, and the chemical treatment can lose effectiveness over time, particularly if the canvas is cleaned with detergents, or scrubbed vigorously. Acrylic canvas used on boats is likely to start losing its waterproof characteristics after a few years — the owner's maintenance of the canvas and where the boat is kept and stored can make a big difference in how long the initial waterproofing lasts.

Acrylic canvas such as Sunbrella can be re-waterproofed, but it is important to use the right type of formula. Never use a silicone-based agent on acrylic canvas. The factory waterproofing uses a fluorocarbon, which is incompatible with silicone, and it would result in a patchy and ineffective waterproofing.

Fluoropolymer and petroleum waterproofing agents are the best agents to use to re-waterproof your canvas. These agents are compatible with the original treatment, and they provide excellent, long-lasting results.

Preparing Your Canvas For Waterproofing

Before applying any waterproofing spray or compound to your canvas, wash the canvas thoroughly first. Then rinse it thoroughly, then let it air dry thoroughly. If possible, it's better to remove the canvas from the boat, because some waterproofing formulas are capable of damaging your boat's gelcoat finish. If you can't remove the canvas, then be sure to cover all boat surfaces around the canvas. You'll also want to protect any isinglass or zippers in the canvas itself; removing the isinglass is best, but at least cover it with foil or plastic sheets, and be very careful to avoid getting any of the waterproof spray on the zippers.

Whatever canvas waterproofing product you choose, be sure to test it on an inconspicuous bit of the canvas first, to make sure it doesn't cause any color changes in the canvas. Most of the canvas waterproofing sprays on the market will work fine on your canvas, but it's better to be safe than sorry.

Start Spraying

When you're finally ready start applying the waterproofing, follow the manufacturer's directions carefully. Most sprays call for two light coats, with the second coat applied perpendicular to the first. Don't overspray; the canvas doesn't need to be drenched and dripping. A light coat covering the entire surface is fine.

Let the canvas dry thoroughly, according the time specified in the instructions that came with the spray. Your canvas should now be completely waterproof again. This type of treatment should least you at least a year, possibly more, depending on how you use, maintain, and store your boat and canvas. You can re-apply waterproofing treatment again when needed.