Category Archives: Refurbishing Leaking Windows

Refurbishing Leaking Windows

When we bought Sanctuary, we inherited several window leaks.  Yes, they were known, but undisclosed, by the seller, not found or tell-tales not recognized and understood by the surveyor, and so, they became ours to discover.  We were the 4th owners of the boat!  The first three owners – over 16 years – had all tolerated these leaks.  We were amazed.  For us, a leak in the non-opening stern window in the aft cabin was at the absolute top of our “must fix” list.  That particular leak, you see, was above the pillow on the Admiral’s side of the bed!  I pulled that window and took it to a glazier to have the glass re-set.  He told us that problem had been there since the original fabrication of the frame.  One glass-to-frame interface still had cosmoline on it, which was the reason for that leak.

Our 1988 Monk windows are set in aluminum frames.  Both the fixed and sliding glass panes are of common tinted safety glass as is available from any glazier.  The frame assemblies are, in turn, set in the fiberglass house/trunk rough openings.  A made-for-purpose structural sealant material is used by glaziers to “glue” glass panes into the metal window frame.  Rated for industrial applications and able to withstand hurricane force wind loads, our glazier recommended Dow Corning 995.  It’s a black “goo” that comes in a tube that fits into a standard caulk gun.  When 995 cures, it does not become hard and brittle; rather, it retains the look and feel of vulcanized rubber.  This allows it to move with the movement of a boat in a seaway.  I also used this same material to seat and seal the window frame assemblies into the fiberglass rough openings in the house and cabin trunk.  Buy it from Internet sources or from a glazier (glass shop).

To remove and reinstall the exterior wood trim, metal window frame assemblies from fiberglass rough openings, and refurbish the insulation weatherstripping, only simple tools are needed.  Tool items can be found at big box home centers or good hardware stores.  Weatherstripping will come from glaziers.  Sealant will come from Internet sources or glaziers:

  • a couple of miniature flat “pry bars.”  These are 6″ or so in overall length, shaped like the letter “L;” i.e., the size used to remove small finishing nails and staples from wooden screen door frames or carpet retainer strips.
  • a couple of 1″ and 2″ putty knives,
  • correctly sized weatherstripping,
  • battery powered drill with a household selection of drill bits,
  • a Dremel tool with a 1/8″ round burr,
  • fiberglass putty,
  • a standard caulk gun,
  • #2 Phillips screw driver,
  • one tube per small window, two tubes per large window: Dow Corning 995 sealant, and
  • a couple of 24″ bar clamps that can be used to pry apart/separate as well as squeeze.

If there is teak wood trim around the windows, the first step is to remove that exterior decorative trim.  Drill out the cosmetic bungs to expose the underlying stainless steel (ss) trim retaining screws, and then remove them.  Don’t be surprised if the fiberglass for some of the wood screw holes doesn’t grip the screw threads, because they were probably stripped when the screws were originally set with a power screwdriver.  That is probably what lead to the sealant failure and subsequent leaks in the first place.

Sanctuary’s windows do not have exterior Teak trim.  On late 80s Monks with aluminum window frames, there are decorative rubber trim molds that fit in a channel in the frame.  The trim hides the heads of SS frame retaining screws.  Between the window frame and the fiberglass, there is a sealant. That sealant is intended to remain weather tight, but if it fails, there will be interior rain water stains and leakage.  Finally, there are is weatherstripping insulation that keeps air from entering around the sliding surfaces of the movable window glass panes.  The 1980s vintage of that insulation is susceptible to age-related UV deterioration.

The metal window frame will be bonded into a rough opening in the fiberglass with a sealant.  It will not just fall out of the fiberglass opening into your hands.  Remove any and all frame retaining screws.  Using putty knives, break the old seal by gently but firmly jamming the blades between the frame and the fiberglass.   Then, work them gently but firmly apart from each other to continue to separate the sealant bond from the fiberglass.   When you’ve got 5″ or 6″ of broken sealant, pry slowly and firmly outwards with the putty knife blades to “encourage” the frame to lift away from the fiberglass of the house.  Once a small but sufficient gap has been attained, slip the short leg of the mini pry bars into that small gap.  Pry with just enough effort to ease the frame away from the fiberglass.  Be careful to exert just enough force to extract the frame, but not so much that the underlying fiberglass cracks or that the frame deforms.  To distribute the prying force on the underlying fiberglass, you can slip a putty knife blade under the fulcrum point of the pry bar.  Once the frame starts to come away, it gets easier and easier to break the sealant until the window assembly will come finally out of the fiberglass opening.  The window glass should be safety glass, and the window assembly will weigh 20# – 25#, so be prepared for the ungainly weight and bulk of that unit when it does come free.

At this point, you have another decision to make.  If you’re going to refresh the weatherstripping in the interior window channels, this is the time to do it.

To get access to the channels that hold and retain the weatherstripping, it will be necessary remove the fixed and sliding glass panels from the frame.  To remove the sliding glass panel, the frame must be slightly spread apart.  On Taiwan-vintage Monk windows, there is a flat metal bar across the full length of the interior bottom of the window frame.  The bar acts as a water dam to create a small reservoir that collects rain water and prevents it from spilling into the interior space.  To spread the frame enough to remove the sliding glass pane from the frame, you will first have to remove that flat bar.  The screws that retain the bar are very small and short.  They are Phillips head machine screws, 6mm – 8mm in length, with fine metric threads.  Use extreme care not to damage the Phillips head seats of those screws!  They can be hard to find. The bar will also be set in a fine film of window sealant gasket material.  Very gently, use the putty knife to separate the bar from the frame.  Do not bend or deform that bar, as doing so will make it virtually impossible to re-install and re-seal without leaks.

Once the bar is removed, use reverse acting bar clamps to gently spread (push) the top and bottom of the frame parts slightly apart.  Spreading the top and bottom very slightly will allow you to remove sliding glass pane from the frame.  Removing the sliding glass panel will give you the clearance you need to break the old seal of the fixed piece of glass, and get it out of the frame.  Finally, you will have access to the channels that retain the weatherstripping.

The appropriate weatherstripping can be difficult to locate.  There are many, many sizes and designs.  I was ultimately successful by going to multiple glaziers in the Sarasota metro area (happened to be where we were at that time) with samples of what I needed.  Storm windows are no longer made with that vintage of weatherstripping, but there are millions of installed units that periodically need repairing, so the stuff is available.  Be persistent.  The weatherstripping comes in rolls, and you should be able to buy it by the foot.  You’ll need 100′ or more to do all your windows.  From the many available sizes of weatherstripping, you’ll need two sizes for your windows. There’s a narrower size for the channels (approx 5/16″), and a wider size (approx 7/16″) that seals the sliding glass pane to the fixed glass pane.  DO NOT TRUST MY MEMORY; TAKE SAMPLES OF WHAT YOU HAVE WITH YOU AND MATCH THEM AS BEST YOU CAN.

To replace the weatherstripping in the channels, I used a Dremel Tool with a 1/8″ burr to open the metal channel about 1/2″ – 3/4″, in an area out of the way of the path of the sliding glass
pane.  That gave me what I needed to slide the new weatherstripping into the channel.  Once the new weatherstripping is in place, use a light but complete coat of 995 to bed the fixed pane in place.  Make sure all of the edges are flat, and squeeze it tight.  Very carefully replace the sliding pane in the channel.  Then use a light coating of 995 on the mating surfaces of the frame and the metal bar to replace the bar.  Work the 995 fairly quickly, as the pot time of that adhesive is only about 15 minutes.

Once the window unit is all back together again, make sure as much of the old, failed, original sealant as possible is removed from the frame flanges.  Also clean up the fiberglass.  Dry fit the window frame assembly into its opening, and use blue painters tape to mask the area just outside the finished fit of the window frame.  The painters tape will catch the squeeze out of the new 995.  This makes cleaning up the squeeze out that results from re-seating the window frame much easier.  Remove the window frame assembly from its dry fit position.  Now is is the time to put epoxy fiberglass filler in any of the screw holes that you previously found to be stripped out.

When you’re ready to reset the window frame, get everything you’ll need ready at the work site. Make sure you have the 995, caulk gun and a couple of putty knives, and lots of paper towels. When you’re ready, take a deep breath, say a little prayer, and liberally and quickly spread the entire contents of the 995 sealant tube around the perimeter of the window frame flange. Smooth the 995 to a 30 degree angle (more to the inside, less to the outside of the frame flange) with a putty knife. Then, immediately lift the frame into the fiberglass hole and set the frame retaining screws.  Tighten the screws a little at a time, and do not tighten any of them
fully tight until all of them are under tension. You should get squeeze out of the 995 as the screws are tightened.  THAT SQUEEZE OUT IS WHAT SEALS THE JOINT AND MAKES IT WATERTIGHT.  YOU WANT T SEE THAT SQUEEZE OUT. The blue painters tape will keep the excess 995 from staining or sticking to the surrounding fiberglass. Once the 995 has had a couple of hours to set up, clean up the squeeze out and remove the painters tape.

Finally, you can re-seat the wood trim.  For that, I’d use a polysulfide sealant, like 3M 101, between the fiberglass and the wood.  Or you can use 3M 5200, but 5200 is a very tenacious adhesive which sometimes yellows in the presence of UV from the sun.  I’d use 101.

OK. That’s what I know. I’ve done several of my windows in this way, and I’m very satisfied with the results. No leaks!

Except for 995 to bed glass and window frames, the only sealant material I prefer to use on the boat for bedding wood to wood, wood to fiberglass, or ss to fiberglass, is 101. NEVER, NEVER, NEVER use household silicon on a boat.  It will not hold up, will not take paint or stain, and will NEVER come off whatever it’s been stuck to.  It is a very undesirable product for a boat!