This sounds well thought out but I have one thought on this. You say you painted the inside of the plexiglass black, the substrate you are now adhering to is paint and not the window itself. I'm thinking you may see the window separate from the VHB tape and leave the paint behind on the tape as the paint is not necessarily a structural bond. Hopefully the paint is more firmly adhered to the glass than the tape will be. Also be aware that the solvents in the paint may damage the plastic over time and cause crazing around the edges. Just a thought. Hopefully I'm overthinking this and wrong. Good luck with the project, keep us posted.
Brent 27-5 Lake Winnipeg Sent from my iPhone > On Feb 15, 2015, at 11:06 AM, RPH via CnC-List <cnc-list@cnc-list.com> wrote: > > I have been reading the recent posts about windows and I thought that some > might be interested to hear of my experience replacing the portlights on my > 1989 30 MKII. Please note that I just started the on-boat part of the project > yesterday and the work is not yet complete. > > In late fall I made tracings of the portlights which I transfered to 1/2 inch > ply. The templates were cut using a circular saw with a guide rail system and > a router. I then took my templates to a local plastics manufacturer, and they > made the portlights from 1/4 inch plexiglass (Bronze 2404). The edges of the > portlights are bevelled at 22.5 degrees (if I remember correctly). They > turned out to be very good reproductions of the factory portlights. > > To ready myself for the project, I also purchased 36 yards of 3M VHB 4991 > Tape 1/2" x 2.3mm, 4 tubes of Dow 795 structural adhesive (I chose white > over black), and a can of DEI 010301 Black High-Temperature Silicone Coating > exhaust paint. > > Yesterday, I attended at the boat with a view to replacing only the aft, > starboard portlight (because I didn't want to bite off more than I could > chew). I knew that the factory portlights were glued on with a methacrylate > adhesive and that they would be difficult to remove. I brought my Dremel > Multimax (which is like a Fein Multimaster) and tried using a flexible > scraper to get between the plexi and the cabin top. This was not effective. > In the end, I used several small putty knives which easily removed the > portlight. > > What the putty knives did not remove was the remnants of the methacrylate > adhesive. I tried several different techniques to remove the adhesive but > ultimately decided that the better course would be to fair the area with 3m > Premium Marine Filler. > > After sanding the fairing compound, I held the new portlight in place while > my wife traced the window opening from inside the cabin onto the protective > paper film. Then I used an Exacto knife to cut the paper along the tracing > and removed the paper surrounding the window opening. Next, I spray painted > the inside of the portlight black with the DEI paint so that the tape and Dow > 795 will not be visible against the cabin top. > > I experimented with small pieces of the VHB tape and was surpised to see that > it did not seem to stick too well to the cabin top even after the surface was > carefully cleaned with alcohol. I decided that the fairing compound should be > left to cure overnight and I will try again today. In any event, I have since > read that the VHB tape needs time to reach maximum adhesion, and that it will > adhere more quickly when the temperature is warmer. I'll bring a heat gun > today to warm up the cabin top before applying the portlight. > > Anyway, if all goes well, the plan is to first affix the VHB tape to the > inside of the portlight. Then, with the portlight dry-fitted in place, I will > affix a few wooden blocks to the inside of the portlight (through the cabin > top window opening) using double sided poster tape. My hope is that I can > then remove the protective film from the other side of the VHB tape and then > fit the portlight into place like a "key" into a keyhole. After the tape is > set, I will then fill the gap around the outside with the Dow 795. > > That's the plan, anyway. > > Robert H. > _______________________________________________ > > Email address: > CnC-List@cnc-list.com > To change your list preferences, including unsubscribing -- go to the bottom > of page at: > http://cnc-list.com/mailman/listinfo/cnc-list_cnc-list.com >
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