Features January 1, 1998 Issue

Apseal & 303 Our Picks to Keep Canvas Dry When It's Wet Out

Of seven brands of fabric waterproofers, we were suprised to discover that market-leader Scotch Gard was one of the poorest performers.

If you’ve ever cursed your way through a sleepless night in a leaky tent in the rain, you know how important water repellency can be. But keeping something from letting water through is not always a straightforward matter. If all you want to do is keep water from going through something, you could just coat it with plastic, rubber, paint or wax. And for some fabric coatings on a boat, such as those used for seat cushions, bumpers, slickers and boots, that’s just fine. The trouble is that for many purposes, a totally waterproof coating will eliminate most of the best properties of fabrics: breathability, inelasticity combined with flexibility, the beauty of the weave and, sometimes, color. For Bimini tops, dodgers and awnings, some interior fabrics, gear bags, canvas deck shoes, jackets and the like, you want the rain and humidity to stay out, but you want the fabric to let air pass through. That’s no simple task for either a fabric or a fabric coating.

Open-weave fabrics are not naturally waterproof. Many modern fibers come with some degree of water repellency added in during the manufacturing process. Bimini tops are usually either vinyl-coated, giving them true water proofing without breathability, or they have a chemical water-repellency treatment that prevents (but doesn’t totally block) water and dirt from penetrating the fabric weave. Some natural cotton duck or canvas also comes pretreated with water repellents. On a quality fabric with a good repellent on it, water will bead up like on the hood of a freshly waxed car.

Eventually, a fabric’s water repellency will disappear. Exposure to the elements and washings that break down the chemicals degrade the fabric and any fabric treatment. Since that’s usually years before the useful life of the fabric has ended, however, applying a water repellent retreatment is a useful and sometimes necessary part of maintenance. It’s the rare fabric that lives outdoors that doesn’t need retreatment after several years, and any fabric that has been washed requires spot retreatment or probably complete retreatment. For instance, if you’ve been spot-cleaning your Bimini top, you’ll probably need to do a water repellent retreatment soon. It’s a worthwhile chore.

We wanted to find out which of the retreatment products on the market work best on boat canvases, especially solution-dyed acrylics, the fabrics used most often for Biminis and dodgers, the best known being the Sunbrella brand, and on natural cotton duck, on canvas jackets, shoes and gear bags.

Stay Away from Silicone
Most common brands of water repellents are silicone-based. However, we didn’t test any silicone-based treatments. Here’s why.

Silicone may work fine for leather shoes and nylon umbrellas, but it’s a disaster on boat canvases. There are two central problems with silicone treatments. First, if a fabric isn’t absolutely clean when you treat it, the silicone will seal the dirt in. Some people describe silicone as a dirt-magnet. A fabric treated with silicone will do a good job of resisting water, but will absorb dirt and create hard-to-clean stains. That will cause more rapid fiber wear. Second, Sunbrella comes from the factory already treated with a fluorocarbon solution. The fluorocarbon chemical is water- and oil-resistant. The molecules run off the surface before wicking through. Silicone retreatments chemically react with the fluorocarbon to negate many of its stain-resistant properties. It may also void the Sunbrella warranty.

What We Tested
We went through the marine and general hardware stores to come up with seven fabric waterproofers or repellents that do not contain silicone. By far the best-known fabric water-repellent treatment product on the market is 3M’s Scotch Gard Water Repellent for Outdoor Fabrics. Scotch Gard is to water repellents what Scotch Tape is to clear adhesive tapes. The brand name is better known than the generic term. Although none is as easy to locate as Scotch Gard, there are six other products we found: 303 High Tech Fabric Guard, Marykate Fabric Water Proofer, Star-brite Waterproofing & Fabric Treatment, Iosso Fabric Waterproofer, Apseal Woven Fabric Protector, and Aquaseal Woven Fabric Protector.

Apseal and Aquaseal, which are difficult to find in the general market, are made by Apco, which also markets them as Uniseal and Sunseal respectively.

The 303 and Scotch Gard are sold as cans of aerosol spray (pressurized and not containing any ozone-depleting compounds), while the others are sold in plastic spray pump bottles. The Star-brite and the Aquaseal are water-based, while the others contain petroleum-distillates, mineral-spirits solvents that improve penetration of the chemical. As we found, the mineral spirits may give off noxious fumes during the curing process, but they significantly enhance the action of the treatment.

The solvents stink and should not be inhaled. Use them in a well-ventilated space. After drying and curing, we found that none of the treatments changed the smell of the test fabrics. All the treatments carry a warning that you should test a spot on the fabric to make sure that colors do not change with application. We used blue and green pieces of Sunbrella and a khaki-colored canvas barn coat for our tests and found no color changes with any of the products.

The mineral spirit-based treatments are flammable, and anytime you use them, keep them clear of all flames, sparks and high heat. Once applied, however, our tests—actually putting flame to the treated fabric—showed that none of the products increased the flammability of Sunbrella.

The other problem with the waterproofers is that they create a slick surface on hard plastics. They’ll make your deck unsafe. Other than spot treatments, you should remove any fabric you’re treating from the boat. Apply the treatment outdoors or in a well-ventilated place where it’ll have time to set.

How We Tested
We took a clean, dry, untreated Timberland cotton canvas barn coat and marked off seven sections of the back, applying each product to a different section. We washed our large blue and green pieces of Sunbrella twice with laundry detergent. This is exactly what the manufacturer says not to do. This washed out most if not all of the factory waterproof treatment. We divided up the test canvases into sections and applied the different products. We followed the standard instructions for all of the treatments, which ranged from “spray two light coats and allow at least two hours’ drying time” to “saturate with a single application and allow 48 hours to dry.” We gave all the treatments a full 48 hours of drying time. The products were applied and allowed to cure outdoors during a very hot and humid summer period.

Finally, the acid test: We took paper towels and sprayed the products on them and hung them out to dry.

After all the surfaces had dried, we put them to the test. We hung up the barn coat and sprayed it with a sprinkler, dousing it thoroughly. We observed the penetration of water by comparing the color change. The wetter the fabric the darker it became. Untreated areas simply soaked through.

We then laid the Sunbrella fabric pieces out and first poured a small amount of water on each section to see if the water beaded up and ran or if it soaked in. We then took a spray bottle and sprayed a mist of water over each section to see if it would penetrate more.

Paper towels are, of course, designed to absorb moisture. What would the water repellents do to negate the towels' absorbency? We poured a small amount on each treated piece.

Finally, we torched the retreated Sunbrella to see what if any effect the water repellents had on flammability. We detected no change. Sunbrella, an acrylic, melts and burns like plastic, no better or worse with the waterproof treatments we tested.

Two Standouts
Two products performed well in every test: Apseal and 303. Where some treated sections of the canvas jacket were thoroughly soaked by the spray, the Apseal and 303 sections stayed largely dry. (The 303 did marginally better.) Both products performed superbly on the Sunbrella tests and made water bead up on a paper towel. Each contains UV ray inhibitors, which are useful in preventing fabric fade, a common marine problem. As we later learned, both products are recommended by Glen Raven, the maker of Sunbrella.

Each contains a mineral spirit-based solvent, which penetrates and bonds better than water-based products. For instance, the Aquaseal, which is made by the same company as the Apseal but is water-based, performed poorly on all tests except the paper towel, which is of course made to soak up water.

The Apseal uses a pump spray bottle. The 303 comes in an aerosol spray can. Recommended application and drying time for both is the same: Apply two light coats, first horizontally then vertically. Neither insists on extensive drying time, although both suggest allowing two to six hours. The aerosol-can spray of the 303 is very convenient. It sprays evenly and has better coverage than the spray mist of the Apseal.

Both should last a long time, unless you wash the fabrics with a strong detergent. The maker of 303 claims it will retain its properties for three years. Apseal makes no such claim. (A little secret is that fluorocarbon products, such as these and the original repellent in Sunbrella, can be rejuvenated to a degree by heat. The danger is that high heat will destroy Sunbrella.)

There’s a big price difference between the two products. 303 costs $14 for a 15.2-oz. spray can that treats 50 square feet of fabric. Apseal costs $17 for a 16-oz. spray container that covers 125 square feet. On a per square-foot basis, the Apseal costs half as much.

The bottom line is that both products are the best on the market for fabric water-repellency retreatment. If you aren’t worried about the price difference, the convenience of 303 in an aerosol spray can makes it the better choice. Apseal comes at a significantly lower price. If you have a large amount of fabric to cover, go with Apseal.

Scotch Gard Doesn’t
Some of the other products performed well on the Sunbrella test and the paper towel test and not on the cotton canvas, while others were the opposite. Marykate and Star-brite both did well on the Sunbrella and the paper towel test, but poorly on the cotton canvas jacket. At $14 for a 32-oz. spray container for the Marykate and $7.30 for 16-oz. of the Star-brite, both are well-priced, but their lack of versatility makes them less desirable. And, the Marykate calls for 48 hours of drying time, which is longer than some of the others tested. Iosso was consistently poor, as was the Aquaseal.

Perhaps the biggest surprise was the weak showing by the Scotch Gard, the market leader. It did a good job on the cotton canvas jacket, a poor job on the Sunbrella and the paper towel. Scotch Gard comes in a convenient aerosol spray can. At a price of $8.99 for a 14-oz. container, Scotch Gard seems to us to be the lowest value of all the waterproofers we tested.

None of the Above
The major problem with any fabric water-repellent retreatment on a boat is that the stuff shouldn’t touch plastics, whether it’s fiberglass or Plexiglas. The solvents can do some real harm. Moreover, most are flammable. So if you’re going to apply a retreatment to a Bimini, shoes, boat cover or whatever, you need to remove or cover any surrounding plastics or take the fabric to be treated off the boat.

Many marinas will send your fabrics out for cleaning and retreatment, saving you a smelly, and time-consuming task.


Contacts— Apseal, Aquaseal, ETI, Inc., 9624 Kiefer Boulevard, Sacramento, CA 95827; 800/767-2726. Iosso Marine Products, 1485 Lively Boulevard, Elk Grove Village, IL 60007; 847/437-8400. Marykate Boat Care Products, P.O. Box 150, Bohemia, NY 11716; 516/244-8550. Star-brite, 4041 S.W. 47th Avenue, Ft. Lauderdale, FL 33314; 800/327-8583. Scotch Gard, 3M, Marine Trades Building, 223-6S-06, Saint Paul, MN 55144; 800/364-3577. 303, 303 Products, Inc., P.O. Box 966, Palo Cedro, CA 96073; 800/223-4303.

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