Hi Pete,
Although you can't pull the VHB apart with your fingers, it would be
very easy (I think) to separate with a blade. Although I haven't tried it,
the tape is quite thick (0.090") and made of a firm acrylic foam, so
cutting the bond should do the trick. A sharp razor blade should be able
to remove the residue.
Gary
S/V High Maintenance
'90 C&C 37 Plus
East Greenwich, RI, USA
~~~~~~~_/)~~~~~~
On Thu, Dec 3, 2015 at 9:17 AM, Pete Shelquist via CnC-List <
cnc-list@cnc-list.com> wrote:
> 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&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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