Prepping for fixed window replacement

[Brian S]

My little O'day has fixed plexiglass windows glued on with Dow Corning 795 silicone (I know, the horror of silicone!) and held by screws while the 795 originally cured.

I'm going to replace, using 3M AHB acrylic closed cell foam tape for mechanical bonding, and filling in the gap with more 795, as recommended by a how-to article in Sail magazine. Those screws were just there to hold in place as the original 795 cured, and I don't like the idea of them prematurely leading to plexi cracking, so I don't want to re-use them.

I know MaineSail has been testing silicone removers, and hasn't found one he likes. So what's my best plan to prep the cabin side gelcoat for the new installation? Clean well with acetone, tape off non-contaminated areas, and then sand with a vacuum to suck up any contaminated dust and reduce the chances of re-contamination?

Thanks,
Brian

 

[Ralph Johnstone]

Those screws were just there to hold in place as the original 795 cured, and I don't like the idea of them prematurely leading to plexi cracking, so I don't want to re-use them.

Standard practice on Hunters is to screw in place as you've said and then remove the screws (when the 795 has set) and fill the holes with black 795. You need a magnifying glass to find them after.

Use sandpaper to remove the old 795.

Haven't heard of using 3M AHB acrylic closed cell foam tape for adhesion. Usual practice is to use the 795 for adhesion then and sealing the edges. I'd be concerned that the tape may allow enough gap that the 795 may not fully contact teh full intended contract surface area.

Attached is an e-mail from Hunter but does not go into great detail on the installation.

Check the archive for some good ideas on removing the old plexiglass.

Always interested in anything else others may have to offer because I'm geting closer to biting the bullet. "Any year now" I keep telling myself.

 

[Merlin Clark]

I really like the idea of using tape. How will do line up the port with the hole when installing? With all silicone you can move it around a bit (messy).
Only thing I'd suggest is if you use silicone (795) instead of tape and there is a curve to the cabin side is to put a spacer in the center of the curve to keep the silicone from being squished out when the ends of the ports are pulled in.
I mounted mine with screws and left them in. Worked for my style boat.

 

[Panta Rei]

My little O'day has fixed plexiglass windows glued on with Dow Corning 795 silicone (I know, the horror of silicone!) and held by screws while the 795 originally cured.

I'm going to replace, using 3M AHB acrylic closed cell foam tape for mechanical bonding, and filling in the gap with more 795, as recommended by a how-to article in Sail magazine. Those screws were just there to hold in place as the original 795 cured, and I don't like the idea of them prematurely leading to plexi cracking, so I don't want to re-use them.

I know MaineSail has been testing silicone removers, and hasn't found one he likes. So what's my best plan to prep the cabin side gelcoat for the new installation? Clean well with acetone, tape off non-contaminated areas, and then sand with a vacuum to suck up any contaminated dust and reduce the chances of re-contamination?

Thanks,
Brian

I have my hatches out and port lights removed ready to do the same job. Removing the old silicone was a breeze using a Scrape right plastic razor blade and simply (hard)rubbing it off with a rag. I did not use sandpaper since silicone is very soft , not something that can be sanded easily. All of the silicone MUST be removed. Acetone won't do a thing to Silicone.
However, I don't know what silicone was used by the PO, it may not have been 795 but it held up well.
I'll likely be using 3M AHB acrylic closed cell foam tape if not butyl rubber in tape form. I have used both and both are tenacious. I''m not drilling holes for screws. I understand that there is no real cure time for these products so clamping force is not needed. (Comments on this are appreciated)

My only issue is that I pulled the hatches and windows last fall and shrinkwrapped the boat. The area has had more than 60 inches of snow and the shrink wrap is starting to fail in spots. It may be a bit wet this spring.

 

[Brian S]

Merlinuxo, here is the article in Sail magazine: http://www.sailmagazine.com/boatworks/replacing-fixed-portlights They recommend the 90mil VHB tape, which gives approximately 2.3mm gap to be filled with the 795 sealant. They say this is about the correct tolerances for the different heat expansion indices for plexi and fiberglass. Also, the VHB will provide both the mechanical fastening and spacing, so no need to worry about squeezing out too much 795 at the middle of the curve radius.

To line up the window without the benefit of fasteners, I will attach wood blocks to the side of the house using double sticky tape. The blocks will form the aft corner and baseline for the window, for exact positioning. Then the window can be fitted into the alignment blocks, then pressed up against the house. Once the tape contacts, there is no repositioning. Also, because the gap between the bottom of the window and the deck is small, I will put a bead of silicone on the plexi, and up some inches on the back side and around the front tip of the window, because I won't be able to get the caulk gun under there. Of course, there will also be plenty of tape on the house side so no oversmear gets down there.

Panta Rei, the problem isn't so much with removing the old sealant from the surface - that can be done with mechanical means like a dull putty knife. The BIG problem is removing the silicone contamination that has seeped into the gel coat. One you put silicone on something, NOTHING ever sticks to it again. Hence the need to sand, but turn the sandpaper often so that it does not gunk up and rub contaminated powder back into the freshly exposed gel coat. That's why I'm thinking of having the vacuum hose sucking at the paper as I sand, collecting contaminated dust. This is why there is no silicone allowed on my boat (except for this application and any potential future plastic framed Beckson items. Prior to my O'day, I looked at a boat that had silicone around every stanchion base, cleat, rub rail lip, and window. (Obviously, it had bad leaks, as borne out by water stains 3" up from the cabin sole.) I passed on that boat like dropping a hot potato! No way was I going to try and re-do that mess of silicone hurt...

 

[dlochner]

3M Caulk Remover does a pretty decent job of breaking the bond between silicone caulk and the substrate. Put it on, let it sit for a while and a plastic scraper will take up most of the caulk. Repeat as necessary.

Ace Hardware stores usually carry it. Or you can find it on Amazon.

Dave

 

[Merlin Clark]

Merlinuxo, here is the article in Sail magazine: http://www.sailmagazine.com/boatworks/replacing-fixed-portlights They recommend the 90mil VHB tape, which gives approximately 2.3mm gap to be filled with the 795 sealant. They say this is about the correct tolerances for the different heat expansion indices for plexi and fiberglass. Also, the VHB will provide both the mechanical fastening and spacing, so no need to worry about squeezing out too much 795 at the middle of the curve radius.

To line up the window without the benefit of fasteners, I will attach wood blocks to the side of the house using double sticky tape. The blocks will form the aft corner and baseline for the window, for exact positioning. Then the window can be fitted into the alignment blocks, then pressed up against the house. Once the tape contacts, there is no repositioning. Also, because the gap between the bottom of the window and the deck is small, I will put a bead of silicone on the plexi, and up some inches on the back side and around the front tip of the window, because I won't be able to get the caulk gun under there. Of course, there will also be plenty of tape on the house side so no oversmear gets down there.

QUOTE]

Thanks Brian!
Sounds like a good plan. Next time I'll use tape.

 

[caguy]

What are you using between the window pane and the inside frame to fill in the gap?

 

[Brian S]

What are you using between the window pane and the inside frame to fill in the gap?

CA, the plexi sticks right to the side of the cabin house. There's a trim ring screwed to the inside, but not much else. O'days are the "Chevy of sailboats" and this is a small day sailer/overnighter, nothin' fancy... To be fair, Precision did the same on many of their boats until switching to opening ports within the past 10 years or so...

 

[Allan12210]

http://hunter.sailboatowners.com/in...mid=267&cat_id=31&aid=8052&page=article&mn=34

Here is the link to how I replaced my fixed windows. I used a butyl windshield material to set the window and establish a gap for the 795. I have now determined the clips I made to prevent the window from falling off (just in case) are not necessary. After a few years the window is still well adhered with no leaks.

 

[Pat]

I'm not certain I'm adding anything but the reason the 795 is the preferred material is because it expands and contracts. That is why it is used by automobile windshield installers. We replaced the side ports on our 272 without paying attention to this and the first hard freeze of the fall fractured the port light into 100 pieces....I called Rudy and he said shame on me for not following his instructions....so we got a new portlight and used the Dow 795 and walla, it is still there holding strong with no leaks 6 years later. As noted above there has to be a gap or an ability of the sealant to expand and
contract with changes in temperature....My for what it is worth.....Pat

 

[jhrusyin1]

Replacement windows

My little O'day has fixed plexiglass windows glued on with Dow Corning 795 silicone (I know, the horror of silicone!) and held by screws while the 795 originally cured.

I'm going to replace, using 3M AHB acrylic closed cell foam tape for mechanical bonding, and filling in the gap with more 795, as recommended by a how-to article in Sail magazine. Those screws were just there to hold in place as the original 795 cured, and I don't like the idea of them prematurely leading to plexi cracking, so I don't want to re-use them.

I know MaineSail has been testing silicone removers, and hasn't found one he likes. So what's my best plan to prep the cabin side gelcoat for the new installation? Clean well with acetone, tape off non-contaminated areas, and then sand with a vacuum to suck up any contaminated dust and reduce the chances of re-contamination?

Thanks,
Brian

Just finished this replacing glass with Lexan polycarbonate sheet, tinted. Old gasket was brittle but found new vinyl from Catalina online (a kit that fit perfectly) and reused old alum frame.
Scrape and peel old sealant to clean. Toluline, alcohol and lacquer thinner help, but elbow grease is main ingredient. All instructions I read promoted: "Clean is not clean enough."
Also, buy vinyl or latex gloves in the economy pack to protect your skin and keep surfaces
clean. The Lexan cuts easily with saber saw, then a belt sander to finish the edges. If you scratch the surfaces, wave a propane torch over the damage to clear it.
For sealant, I used butyl rubber strip, which means you will have to keep the screw fasteners.
Hope you splash early.

 

[stevemac]

My little O'day has fixed plexiglass windows glued on with Dow Corning 795 silicone (I know, the horror of silicone!) and held by screws while the 795 originally cured.

I'm going to replace, using 3M AHB acrylic closed cell foam tape for mechanical bonding, and filling in the gap with more 795, as recommended by a how-to article in Sail magazine. Those screws were just there to hold in place as the original 795 cured, and I don't like the idea of them prematurely leading to plexi cracking, so I don't want to re-use them.

I know MaineSail has been testing silicone removers, and hasn't found one he likes. So what's my best plan to prep the cabin side gelcoat for the new installation? Clean well with acetone, tape off non-contaminated areas, and then sand with a vacuum to suck up any contaminated dust and reduce the chances of re-contamination?

Thanks,
Brian

2 years ago I replaced the 4 coach top side windows on my Hunter 35.5. I hired a guy that had retired from Carver Yachts in New Bern with 15 years experience to change the (2) on the starboard side, after watching him I changed the remaining 2 on the port side following his steps. I easily removed all 4 windows just by pushing them out, the adhesiveness of the Dow 795 had become so lose on the factory original windows. I purchased a 4 x 8 sheet of smoked Plexi Glass from a local plastics shop and rough cut the window sizes on a table saw. Once the windows were removed, using a trim router the window sizes were duplicated and interior bevel made to match the Hunter factory windows. Using a plastic putty knife most of the the original DOW 795 was removed, using mineral spirits and a 3M scrub pad the remaining DOW 795 was removed and cleaned up with mineral spirits and denatured alcohol (no acetone). Once dried the window frame was sanded with 100 grit and cleaned again with mineral spirits and denatured alcohol. The mineral spirits cut the old silicon pretty good.
Centering the windows with rubber standoffs and holding the windows in place with tape, an exacto knife was used from inside the boat cutting the outline of the window into the backing paper of the plexiglass, the paper was then removed exposing only the surface that the DOW 795 would make contact for adhesion to the window frame, this area was lightly sanded with 100 grit roughing it up for better adhesion. Approx 1/4" thick rubber spacers were obtained from a local glass shop and tacked into place with Dow 795 so as to provide a void to fill with the 795, the inside and outside of the window frame was tapped very heavily to prevent the 795 from making a huge mess. Once the rubber standoffs had a good head start drying (about 30 minutes) the windows were dry fitted, centered horizontally and vertically using additional about 15 rubber standoffs per window. Once the alignment was satisfactory the windows were removed and Dow 795 applied (don't go crazy here else you will have a huge mess to clean up) filling just over the thickness of the rubber standoff so that the black appearance between the back side of the window and the window frame was uniform with no bubbles allowing white to show through then the window pressed into place and a final cosmetic caulking around the edge of the window, smoothed and cleaned up with the handle end of a putty knife for a very smooth appearance. Note screws were not needed to hold the window in place the Dow 795 itself had enough adhesion to keep the window in place while the silicon started drying. After clean up squeezed out silicon, in about 2 hours all tape was removed and final cleaning performed. The next day the inside paper was removed from the window and a final clean up performed using denatured alcohol. I have heard of people using screws and even duck tape to hole the windows in place while the silicon started its curing process, I found these were not needed, so far 2 years and no leaks. You can actually get 2 complete sets of windows out of the 4 x 8 sheet of plexiglass so you can have a spare set if desired, make sure you cut the spare set before you throw away the original windows. OR you can cut replacements for the non-opening port lights that are in the hull (5 of them for a 1994 Hunter 35.5), I did the later and replaced the starboard non-opening port light this past fall. The temps turned below 51F before I could replace the non-opening on the port side, once spring gets here that will be my next project as the Dow 795 has a low temperature working limit of only 51F. Any temps below 51 that 795 can have problems curing and possibly the curing process stopped if below 51F for any significant amount of time. When replacing the coach top side windows it is advisable not to sail the boat boat for ~ 10 days so the top does not flex until the silicon is essentially 100% cured. The cost of the plexiglass was ~ $170 for the 4x8 sheet. A peer purchased his windows from Hunter while they still provided parts and paid ~ $200 each for his 4 windows, cutting and shaping the windows was easier than I thought as this was my first time working with plexiglass, about 3 hours to cut and shape all 4 coach top windows, about 2 hours to cut, shape and drill the non-opening hull windows, Dow 795 less than $10 tube, I purchased 8 tubes of the 795 and used all of them, recommendation here is to purchase 6 or 8 for one side (port or starboard), see far that goes depending on the size of your windows and how happy you get with the caulk gun then purchase enough to finish the project for the other side.

 

[BLIGHT]

Steve
I also have a 35.5 and need to replace the large cabin windows on the sides. On the port side they are crazed. Do you have the thickness of the material that you used?
Thanks

Bob

 

[Bob McKee]

I replaced the side windows on my S2 9.2A with 3/8" Plexiglas that I bought at Commercial Plastics in Seattle. I installed my ports with stainless steel Phillips head bolts, dimpled washers with a neoprene sealing washer attached and T-nuts glued on the inside of the hull. Most of the interior wood was removed to access the window area, the wood pieces were screwed into place and are easy to remove. I used 1/8" butly window installation tape between the window and the hull, be sure to open the bolt holes in the tape before installing them so the bolts don't wind up the tape when you tighten. I used 3/16" thick Plexiglas 10 years ago and should have used 5/16" or 3/8" because the windows are starting to crack, thicker plastic would stand up better, I intend to increase the number of bolts on the long axis of the ports when I replace them again . The windows were cut to shape by Commercial Plastice in Seattle but the plastic is easy to cut with a router and tracing bit and that is what I would do now that I have learned how to do it. There should be a plastics retailer near you that can supply and advise the best plastic to use. I was told that Lexan is stronger but less resistant to sunlight. In my opinion, I wouldn't attempt the factory installation method. Bolts will hold, seal alone won't and I couldn't stand to deal with the mess. I used large head SS 3/16" bolts, neoprene faced, dimpled washers with SS t-nuts on the inside. The holes in the plastic are 7/32" to allow for movement (the bolts don't touch the plastic). The SS screws and washers came from Tacoma Screw, but there should be fasteners available where you are. I have seen several boats here in the NW using bolts, the ones that used seal instead of window tape are generally messier that mine. I simply won't rely on seal alone.