Does anyone have experience using 3M VHB tape to bond windows to cabin top?

[russp]

After 26 years the bonding silicone on my "sun exposed" side windows has failed and they are leaking. Trying the easy way to seal with Sikaflex 291 didn't wokk as it didn't stick to the acrylic window so I am now preparing to remove the windows fully and do the job properly.

It appears that use of double side Very High Bond tape is now in routine use and potentially a lot less messy than bedding the window against a bead of silicone. Has anyone used VHB tape and how did it go?

[Wisail]

I to need to do this. I am researching this and would appreciate information as well. I understand you need a minimum thickness of tape to allow for expansion and contraction. I think you still need to caulk around the outside.

[wisski]

I did this 2 years ago. I used the 3M VHB double-sided adhesive tape, 2 Rolls, I think. I don't remember if it was 1" wide or the 1/2". What left over is on the boat, and I am not there right now. I stuck the VHB to the fiberglass lip on the hull. Removed the window, clean it up, scotchbrite the lip, then I pressed the window back into place onto the VHB. Used DOWSIL™ 795 Silicone Building Sealant I purchased from Menard's and ran a bead around each window. Choose the DOWSIL™ 795 because it is structural rated, UV rated, and is used to hold windows into skyscrapers, which as we all know flex considerably. Been leak free since.

[russp]

Hi Rob,

There are about 1000 variants of 3M VHB tape, do you recall what the specific designation of the tape you used was?

Regards

[cuthbert]

window.jpg (222.43 KiB) Viewed 106 times

If I'm reading this correctly, I had the same problem about 10 years back, leakage from the top of the largest fixed widow on the starboard. I was about to pull the window out and reseal with a new complete install and someone in my marina suggested .....stick something slim in and lever the window slightly to enlarge the gap then clean the mating surfaces as best you can and apply in the gap clear 3M silicon. I did this and made sure I had plenty to cover the top of the join to prevent further ingress. This seemed to fix the problem for about 30 minutes work. I haven't had a leak again since then, I'm mindful I may have to go back one day and remove completely and reinstall but for now it appears to be a sound and effective solution.

JC

[wisski]

Got out to the boat, I don't have any of the package left. The remaining tape just says 3M on it. It is a double sided foam tape for holding on automobile trim.I know that I got it at the local auto parts store.

[russp]

Well that is pretty much what I did except didn't lever the acrylic out far enough to attempt to clean the mating surfaces, I applied Sikaflex 291 same way you did and thought "job done" but within a few weeks the acrylic and fibreglass/old sealant bond had failed totally. Nice new layer of sealant on the cabin side though!!

[tranquil]

Here’s the information regarding caulking plexiglass/lexan port windows we did 2 years ago and they do not leak:

Catalina Yachts used Dow Corning Dowsil 795; black; ( I called them) which I used. It is also used in airplanes, office buildings and skyscraper windows. Bought it from Amazon. Previously used Sikaflex which did not hold for long.

Since just a portion of the plexiglass/lexan port windows popped out ( I did not want to remove the entire port window)...Just repair not replace.

My port windows sit in a 1/8” gap between the inner and outer hull. We inserted the Dowsil on the inside (as best possible) and pressed the glass against it from the outside; taping it down from the outside to dry. To fill the gap on the inside.

Days later, caulked the outside of the window. I taped it first; Pete did the caulking. He laid down a thick bead in a section, then smooshed it in with a gloved finger, then removed the tape and gently smooshed over again to smooth it out. Very messy stuff to work with; I bought a bottle of Goo-Gone for caulk which was handy; also denatured alcohol with wipe rags and he used both. The windows have not leaked since.

If we have to remove the entire window in the future, will scrape out old caulk and put molding tape on the inner side of the plexiglass all around the flat side at the edge. Think is supposed to act as an additional barrier to prevent leaking to the inside should water penetrate the caulk. Is from Amazon: 3M Super-Strength Molding Tape, 03616, 7/8 in x 15 ft, 1 Roll

In the future if we have to remove the entire window, part of the plexiglass is adhered to part of the hull of the boat that is painted black so that it looks like the rest of the port. Removing the entire window will remove the black off this part affixed to the hull and will need to be repainted or will show thru the plexiglass when repaired. I bought Duralux Marine Coatings in Black for this purpose.

Hope this helps.

[russp]

Wow, thanks Teri, does it what! I did what you guys did initially with Sikaflex Marine and it was a failure, only stuck to the plexiglass for a few weeks. I actually asked Google AI how to do it yesterday and it came back with a complete and very sensible approach. To use 3M VHB 5962, how to prep the surfaces, suggested could use 3M Tape Primer 94 to get an even stronger bond, and to seal the outer edge of the interface against weather with Dow 795.

Seems to be the "norm" now if you have removed the whole window and cleaned up both surfaces.