Just an observation; The VHB tape seems like a more simple installation. However, I’m curious if Plexus is evil because it’s too hard and tenacious, yet the VHB joined parts won’t come apart, in 5-10 yrs when redoing windows again it sounds like we’ll be calling VHB evil.
I don’t have a better solution, and question if there’s really a good one out there. It sounds like we need to keep templates of the lenses and deal with cutting and filling around the frame when the connection fails. From: CnC-List [mailto:cnc-list-boun...@cnc-list.com] On Behalf Of Gary Russell via CnC-List Sent: Wednesday, December 02, 2015 7:47 PM To: C&C List Cc: Gary Russell Subject: Stus-List Bonded Windows (continued) For those who were following my post on bonded windows on High Maintenance, I have an update and many thoughts on the project enumerated below. I have successfully installed two windows on the starboard side and replaced the acrylic on all the hatches and can say that the project has been very successful. I have terminated my project at this point as the temperatures are now too low for the VHB tape which requires a temperature of greater than 60 degrees F for application. Here are my observations: #1. Plexus is evil stuff and should not be allowed on a boat. It is too hard and tenacious a bond. Because fiberglass and acrylic have such a different expansion coefficient, fracture of the acrylic is assured. Removing the stuff is impossible without destroying the gel coat underneath. I tried a sharp blade between the fiberglass and the acrylic and all I managed to do was rip up the gel coat. #2. Before removing the windows, make a template out of some thin plywood (or other material) because the window will (no doubt) come out in pieces and you will have nothing as a reference for making the new windows. #3. I finally was successful removing the acrylic with a 5/8” router bit set to a depth equal to the thickness of the acrylic plus the thickness of the Plexus. I actually used a Roto-Zip instead of a router as it had a smaller footprint and was easier to handle. I free-handed the router to cut through the acrylic and into the Plexus. It’s risky but effective. Don’t cut all the way around the perimeter, but leave tabs to support the window. Otherwise, the window will sink under the weight of the router and you will cut into the gel coat. You can break out the tabs later. #4. Once the windows were out, I used West System epoxy thickened with low density filler to repair any damage to the gel coat. Fortunately, all my gel coat damage was limited to the area under the windows. Once the windows are out and the damage is repaired, the rest is fun and easy. #5. I cut the new window out of 3/8” Plexiglas using a pattern router bit (sometimes called a Formica trimmer). I used masking tape folded in half lengthwise to stick the new Plexiglas to the old window (or template). I ran the tape at right angles to insure that they wouldn’t slide in either direction with respect to each other. It does a very nice job and is quite easy. I then used a 1/8” round off router bit on the outside edge of the new window for cosmetic reasons and a 45 degree chamfer bit on the inside edge to make room for the Dow Corning 795 silicone. #6. I installed the 3M VHB 4991 tape on the coach roof and masked around where I wanted the window to go. This would help me locate the window and provide the masking for the Dow Corning 795 silicone to follow. I also masked the edge of the new window for the same reason. #7. Now cones the tricky part. You only get one shot with the VHB tape, because once it is down, it is not coming up. I tried adhering two small pieces of acrylic to each other with about two square inches of VHB tape, and I can assure you, you won’t pull them apart. VHB is amazing stuff. As a guide, I mounted two small wooden blocks to the masking take below the window with a small piece of VHB tape. By attaching it to the masking tape, I was sure I could get it back off. Actually, VHB doesn’t stick very well to masking tape anyway. I also stuck a small wooden block to the masking tape at one end of the window as well. This allowed me to set the window on the two bottom block and then slide it over to the end block before pushing the window into place. By all means, make several trial runs with the film still on the VHB tape before removing the film. Once the film is off you are committed. I pushed the window in place and it looked perfect. Then it is simply a matter of squirting the Dow Corning stuff into the gap and smoothing it out with a finger. As soon as the silicon is smoothed out, you can remove the masking tape and pour yourself a stiff one, while you admire the fine job you have done. #8. There was concern expressed that the VHB tape would be visible through the window, and it was suggested that the window should be painted with Krylon Fusion Black. Actually, the VHB tape is the same color as the Plexus which is not visible, so the VHB won’t be visible either. No paint is necessary. I used the darker shade of grey Plexiglas and can say that it look spectacular. The darker shade really “pops” and the contrast is particularly attractive (in my humble opinion). The darker color makes it difficult to see into the boat, but has a minimal effect when looking out. The VHB is not visible at all. #9. There was also concern expressed concerning whether the curvature of the coach roof would cause a flexing force to peel the VHB tape. I can say that the radius of curvature is very large (>20 feet) and the forces are thus very small. 3/8” acrylic over those lengths is quite flexible. I see no problem at all. #9. I have posted some pictures on Google Drive and I think you can view them at: https://drive.google.com/folderview?id=0BwQRSP2fYIFmemxYOGlVcHNUNVk <https://drive.google.com/folderview?id=0BwQRSP2fYIFmemxYOGlVcHNUNVk&usp=sharing> &usp=sharing I am new to posting pictures, so if you have trouble seeing them, email me and we can get it fixed. I will add more pictures as they become available. #10. Needless to say, I am thrilled with the outcome so far. I have also re-glazed the hatches using the Boatworks video and they came out spectacular as well. The only difference I made from their recommendations is that I bedded the acrylic in butyl tape instead of the Dow Corning 795 because it was much easier to get a uniform bead and that was the way it was done from the factory. I still filled the gap around the windows with the Dow Corning 795. Boatworks is right, the Dow Corning 795 is nice stuff. #11. If I have left anything out or you have any questions about this post, just give me a shout. Gary S/V High Maintenance ’90 C&C 37 Plus East Greenwich, RI, USA ~~~~~~~_/)~~~~~~
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