Fix Those Leaky Windows!

The most common cause of water leaks into the cabin of a first generation C-22 sailboats besides the chain plates, are the aluminum frame windows. The silicone that seals the glass to the frame eventually loses its adhesion and elasticity and separates from the glass. Water accumulates in the vinyl glazing channel, which isn’t watertight, and works its way into the cabin, causing mildew and odors.

Many owners think they need to completely remove, disassemble, reassemble the windows with new vinyl components, and reinstall them but that’s overkill. You don’t need to buy an expensive kit and spend days or weeks in frustration to solve this simple problem. You can do it in an afternoon for under $20.

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First, let’s understand how the windows are built so that we know what to do.

The aluminum frames are made from an extrusion with several channels like the picture below.

Section view through window extrusion

It was probably a standard RV design back in the day, intended to hold two panes of glass, at least one of which was moveable. Catalina Yachts probably contracted an RV window manufacturer to build their windows for them but with only one, non-moveable pane of glass in the outer channel. The unused inner channel is filled with a vinyl molding that serves no other purpose than to take up the empty space.

Note that the frame flange is sealed to the fiberglass cabin walls with a very strong butyl rubber adhesive. It’s very unlikely to leak there. Unless you’re going to completely strip the cabin to paint it or you need to replace the glass, I don’t recommend trying to remove the frames. Even then, I’d consider leaving them in place and masking them, if possible. The butyl is so strong that you’ll probably damage the frames beyond repair and new replacements are no longer available.

The glass is held firmly in the frame by a vinyl glazing channel. It’s water resistant but not waterproof, especially where bent around corners in the frame. The real waterproofing is done by silicone sealant in the gap between the glass and the frame. You only need to replace the sealant and everything else can stay in place while you do it. I recommend using the best commercial grade silicone that you can buy–one formulated for window installation and containing UV inhibitors like Dow Corning 995 Silicone Structural Sealant. It’s available in several colors. I chose a medium gray. One tube is more than enough for the four windows in a C-22.

The trick to removing the sealant is to make three specific cuts where shown as red dashed lines in the picture above and described below.

Tools and supplies you’ll need:

To remove and replace the silicone sealant:

  1. Cut the silicone free from the frame edge by holding the blade perpendicular to the glass and pulling it carefully around the frame.
  2. Cut the silicone free from the frame channel by inserting the blade 1/8″-1/4″ into the silicone parallel to the glass and pulling it carefully around the frame, keeping the blade flat against the frame. Don’t cut any deeper than necessary or you might cut the vinyl channel.
  3. Cut the silicone free from the glass by inserting the blade 1/4″-3/8″ into the silicone against the glass and pulling it carefully around the frame, keeping the blade flat against the glass. Don’t cut any deeper than necessary or you might cut the vinyl channel.
  4. Pull the silicone out of the frame. It should come out easily and mostly in one piece.
  5. Use the blade to remove any remaining silicone in the frame.
  6. Use the nylon brush with rubbing alcohol to clean out any dirt, debris, or algae that accumulated between the silicone and the vinyl channel, especially in the bottom of the frame where water might have settled. The cleaner you get that space, the better the seal will last.
  7. Apply the masking tape to the outside edge of the frame and to the glass 1/4″ inside the edge of the frame.
  8. Use the calking gun to inject a bead of silicone between the frame and the glass and fill the space between the tape lines.
  9. Use the small putty knife or similar tool to form a smooth, consistent width and angle in the silicone. Hold one corner of the tool against the edge of the tape on the glass and the edge of the tool against the edge of the frame. Let any excess silicone squeeze onto the tape but not onto the frame or the glass.
  10. After the surface of the silicone has cured slightly but while it is still soft, remove the tape to leave sharp, clean edges.
  11. Allow the silicone to cure completely before letting other objects contact the silicone or washing the sailboat.

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3 Comments Add yours

  1. guerdon says:

    Use low viscosity silicone for auto window glazing. It is designed for repairs without having to. remove any thing. a small squeeze tube will do the whole boat.

  2. John Semans says:


    Great to see new content! I will definitely be doing this project!


    Sent from my iPhone


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