Maintain Waterproofing on Canvas Bimini & Dodger

I’m sure there are worse things than a leaky drippy canvas bimini and dodger, but during a weather trough that parks on us for a week dumping gallons and gallons of free fresh water, ruining my family room (i.e. cockpit) and keeping me imprisoned below in 18′ of living space … but at the time I get cabin fever and can’t think of too much worse!

When we bought Winterlude in Annapolis, MD, there was a dodger.  No more canvas, just a dodger.  One of our first projects getting the boat outfitted for cruising to Florida was to add a bimini for shade.

Contrary to what we thought, we quickly discovered that Cadet Grey Sunbrella does not last as long in the real tropics as darker colors – go figure. We replaced our bimini once by bringing a new one back with us on the plane and had both the bimini and dodger restitched, it seemed like every other year.

Usually we treated the canvas as recommended by Sunbrella with 303 Fabric Protectant.   It worked until it didn’t.    We assumed, incorrectly as it turns out, that the 303 Fabric Protectant got less effective as our canvas got older and we turned to drastic measures.

Thompsons Water Sealing our Old Bimini - Not Recommended!

Thompsons Water Sealing our Old Bimini – Not Recommended!

If it seems your 303 isn’t as effective as it once was, the culprit is likely DIRT in your canvas.  What happens is 303 works to waterproof the canvas until the next heavy rain, which washes the dirt right out from under the 303 and guess what happens!  But we didn’t know this AND we were out of 303 Fabric Guard – we had to take it with us every year and finally after a treatment in Panama, we ran out of 303 sitting in a week’s torrential downpour left over from Hurricane Ida in Roatan.  By the time we got to Belize, we had several more months of cruising left and we were desparate.  We bought some Thompson’s Water Seal at the local hardware store since it was the only thing we could get and we water sealed our canvas.  It worked fine for awhile, long enough to get us back to the US where we were planning a new cockpit enclosure so it was no longer an issue.  Not sure we would have used the Thompson’s Water Seal had we been planning on keeping that canvas!  It’s NOT recommended by anyone, including us.   We had tried it before on a backup bimini – here’s David painting it on while still in our driveway – that was the year we took a brand new bimini and the old water seal treated version as a back up with us to the Rio Dulce, Guatemala.

You’re left assuming the 303 no longer works.     But just as we were wrong, you’d be wrong too!

303 Fabric Guard

303 Fabric Guard, Recommended by Sunbrella

Here are the specific instructions copied directly from the 303 Fabric Guard website, link here to view the 303 website and more information:

When it’s time for a thorough cleaning, Sunbrella fabrics can be cleaned while still on a boat or, size permitting, they can be removed for cleaning in a washing machine or dockside. When cleaning Sunbrella fabrics, it is important to observe the following:

  1. Always use a mild soap such as Ivory Snow, Dreft or Woolite.
  2. Water should be cold to lukewarm (Never more than 100°F/38°C.)
  3. Rinse thoroughly to remove all soap residue.
  4. Air dry only. Never apply heat to Sunbrella fabrics.

General or light cleaning

To clean Sunbrella while still on a boat, follow these simple steps:

  1. Brush off loose dirt.
  2. Hose down.
  3. Prepare a cleaning solution of water and mild soap such as Ivory Snow, Dreft or Woolite (no detergents).
  4. Use a soft bristle brush to clean.
  5. Allow cleaning solution to soak into the fabric.
  6. Rinse thoroughly until all soap residue is removed.
  7. Air dry.
  8. May not require re-treatment depending on the age of the fabric.

If stubborn stains persist, you can use a diluted chlorine bleach/soap mixture for spot cleaning of mildew, roof run-off or other similar stains (see our Stain Chart for specific recommendations).

Heavy cleaning for stubborn stains and mildew

Sunbrella fabric does not promote mildew growth, however, mildew may grow on dirt and other foreign substances that are not removed from the fabric. To clean mildew, or other stubborn stains:

  1. Eight ounces (one cup) of chlorine bleach.
  2. Two ounces (1/4 cup) of mild soap and/or detergent.
  3. One gallon of water.
  4. Clean with soft bristle brush.
  5. Allow mixture to soak into the fabric for up to 15 minutes.
  6. Rinse thoroughly until all soap residue is removed.
  7. Air dry.
  8. Repeat if necessary.
  9. Re-treatment of fabric for water and stain resistance will be necessary.

View the Sunbrella fabric Stain chart.

Remember to protect the area around your Sunbrella fabric if using a bleach solution. Carpet or other fabrics that are not Sunbrella may have an adverse reaction to the bleach. If a boat cover is suitable in size for a washing machine, these steps should be followed:

  1. Use mild soap and/or detergent.
  2. For heavier stains add 1 cup of bleach to wash.
  3. Wash and rinse in cold water.
  4. Air dry. Never apply heat to Sunbrella.
  5. Re-treatment for water and stain resistance will be necessary after machine washing.

Re-treating the fabric

As part of the finishing process, Sunbrella fabrics are treated with a fluorocarbon finish, which enhances water repellency. This finish is designed to last for several years, but must be replenished after a thorough cleaning. Based on test results,
Glen Raven recommends 303 High Tech Fabric Guard™ as the preferred re-treatment product for Sunbrella fabrics. Fabrics should be re-treated after thorough cleaning or after five years of use.

For more information on re-treatment products, please visit


Do you have other recommendations on how to best preserve canvas waterproofing?  Please leave a comment and share the information!  THX!  Jan


  1. Very nice, i suggest webmaster can set up a forum, so that we can talk and communicate.

  2. Here’s a tip for you, don’t get any other colored fabric other than blue or green. The reason is that the colors are closer to the end of spectrum of light, that is further from the end of the spectrum where damage is done. Look at a graph of the spectrum and you will see that red it closer to the ultraviolet color and gamma rays. This is the end that does the damage. Here’s the thing most people don’t know. That grey, yellow, brown, and a lot of colors, actually have a couple of red threads running thru the fabric. Well, those are the ones that shred in the sunlight. Thought this might be of interest.
    s/v Renasci

    • Thanks s/v Renasci – our canvas maker convinced us to go with dark canvas (rather than the cadet grey that came on the boat) because he claimed it would last longer. I’d never heard why. Now I know why it seems like red fades the fastest – whether gelcoat or canvas. 🙂 Cheers! Jan

    • I can’t comment on what color fades fastest or why, but I can correct the mis-statement above about red being closer to the ultraviolet color and gamma rays. Red is at the opposite end of the spectrum (i.e. it is the color furthest from UV). Violet is at the end closest to UV and red is at the other. That said, it still MAY be true that reds fade faster, just not for the reason given.

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