In this video I mount some new fixed portlights using 3M VHB tape. VHB stands for Very High Bond, and it does exactly what it says it does! When installing polycarbonate or acrylic panels / portlights I’ve found this method to work extremely well. It eliminates the need for any kind of screw fasteners which typically result in cracking the material, provides a nice clean look and allows the poly / acrylic to expand and contract with temps without issue.
The specific tape I used was 3M VHB 5952 and can be found through a number of online retailers. At the time I ordered, I happened to find the best deal through an Ebay seller. I went with 1″ wide tape as it’s what my project called for, but it comes in different widths and roll lengths.
The caulking I used was Dow Corning 795 in black. Dow Corning 791 would also be a great choice. I typically order this material from here.
What I particularly like about this silicone is the working time and it’s bonding strength. Unlike most silicone’s, this caulking allows roughly 10 minutes of working time before it starts to skin over (most others allow a minute or less) so, you have plenty of time to smooth it over and pull the tape.
These portlights were roughly 24″ wide and 8″ tall. Each tube of caulking was able to glaze 3 portlights before it was empty.
One tip I would like to suggest for anyone looking to cut and install their own portlights would be to allow a generous gap / reveal of at least 1/8″ all the way around the polycarbonate. You’ll need this space to completely fill with silicone around the portlight and get a good seal.
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Materials, Tools, & Suppliers
- 3M VHB 5952 Tape
- Dow Corning 795
Thanks!! That VHB tape looks good.
What is the reason you don’t use polyurethane?
This silicone is better 😉
Curious question, and thanks for the videos, they are great help. Ok question. How does this 3M and the Caulking hold-up to the south’s summertime heating? The acrylic expands and contracts, in your opinion does this shorten the life of the caulking? And does this 3M product allow for expansion of attached products?
Thanks
Dale
Yes, both products are designed to allow expansion without loosing bond. As far as I know both products work very well in both hot and cold climates 🙂
Loved the video – thanks for turning me on to 3M VHB and Dow 795 silicone.
I’m installing some windows about the same dimensions as your. These will lie flat on the cabin top. My concern is that the area of overlap will show through the acrylic. I’d like to paint the overlap black, but don’t want to mess up the adhesion of the VHB or 795. Could you suggest a paint?
Thanks!
John
It will be best if both the 795 and vhb are applied directly to the clean plastic; I wouldn’t use any kind of paint :-). If you’re referring to the overlap of the tape being visible, there shouldn’t really be any overlap. All tape edges are butted up to one another; not overlapped. If I’m misunderstanding please let me know.
Thanks!
Is it possible to convert framed portlights to fixed?
Sometimes, it mostly depends on how the mounting surface is shaped. Anything is possible, but whether the work involved is justified is another question 🙂
Hi Andy,
I’m in the process of redoing my portlights on my 34 C&C. There is a slight curve in the cabin profile where the port lights would be installed. The VHB product you speak of…would it handle the flexion of the curve and the possible torquing of the cabin sides in general without letting go? Also would like to know if it’s a good idea to paint the finish openings prior to using the VHB or should I adhere it to epoxied glass? Thanks ahead of time and thank you for your great information!
Hi Marits!
As long as the poly / glass you’re installing isn’t too thick the vhb tape will absolutely be strong enough to hold with the contours and flexing of the sides. I’ve done large panels that had a pretty good curve to the sides and they have not let go in over 5 years. They don’t look like they’re going to anytime soon, either 😉
I’d try to avoid using any material that is thicker than 1/4″ slightly thinner would also work. This material is very strong. The key step is making sure that all mating surfaces are clean! Wipe the glass and boat with a mixture of denatured alcohol and water 50/50 mix. Wipe it dry, and repeat. Wear rubber gloves to avoid any oils from your skin getting onto the surface.
I find it easiest to apply the tape to the glass rather than the boat. Trim off any excess and it’s very helpful to have another pair of hands for setting it in place on the boat. You only get one shot 😉
Also, as long as the paint you’re using has a good bond to the fiberglass there shouldn’t be any issues applying the tape over the paint. I’ve not tried this with 1 part paints, but have never had an issue doing this with 2-part paints. I guess, when in doubt make up a small test panel to see if the paint pulls up.. But, most likely it will work fine!
Hope this helps!
Good luck!
Hello Andy!
I have a Crown 34 sailboat, (later the hull became thevSan Juan 34) I am going to remove the 4 portlight windows, and will be ordering a long single piece of 1/4″ acrylic to cover all the jokes at once. There will be alot of surface area between the portlights and past the forward one where I will taper it off to follow the contour of the deck as it goes forward. I’d like your opinion on two things.
1. What do you think the minimum width of VHB tape would be that eould effective around the perimeter of the openings for the portlights (not recessed)
2. Do you agree that I should cover the entire surface of the glass where it will contact the fiberglass once installed to ensure long lasting bond?
Thanks for your input!
James
Hi James!
Homestly I think the best appearance would be had by addressing each window individually. I think I also saw your Q on FB, but for some reason the pics of your project didn’t come through :-/ Could you try resending? Thanks!
What thickness of vhb tape do you use?
I don’t recall, but the product # us mentioned in the description… Hope this helps!
Hi Andy, Great site. Just wandering what is the make and model of this boat. Beautiful!!!
Hi Randy,
This was a Ranger 37 that I re-painted 🙂 Thank you!!
Thank you !
I just became a “Patreon” yesterday. “A workman is worthy of his hire”. Your labor of love (the videos) are surely worth being supported by those who reap the benefits.
I have a 1973 Allied Mistress ketch (39ft) and need to do something with the port lights. The are eight opening and two fixed. I really like the look of what you did in this video. My question is this, since the opening port lights are glass in aluminum frames would it be possible to use safety glass rather than polycarbonate for the fixed lights that I have now? I have a source for safety glass (laminated with the plastic between the layers like automobile windows) that can cut them and bevel the edges just like you did with the poly. My reasoning is that the glass will last much longer and be much more resistant to scratches and crazing than the poly.
Your thoughts!
Hi Andy,
Can you tell me what kind of glass product you have used?
Thanks!
Thanks for the video..I am about to replace four fixed ports on my 35.5 hunter legend….after completion how long do you wait to remove tape?….immediately, an hour or so or the next day?…thanks….You do great things..
Hi, Andy. I need to replace four frameless portlights like the ones in your video that were installed a couple of years ago using Sikaflex 295 that are now leaking, and one just popped out yesterday when I gave it a slight tug. There is a nice flat smooth surface of Sikaflex underneath that would be hard to remove, so I am wondering if I can use the 3M VHB tape on that surface to replace the portlight. I realize, however, that I need to remove the Sikaflex in the gap on the outside edges, so I can seal them with the Dow Corning 795, so I wondering if you have any suggestions for how to remove that part of the Sikaflex in such a way that I don’t damage the fiberglass underneath and around it.
Hi! Does the VHB tape form a waterproof seal as well or is it strictly for adhesion with the silicone caulk providing the only waterproof seal? We have a catamaran with a large (5 feet by 2 foot) poly window where the Sika 295 has failed in one spot resulting in water ingress. Would the VHB tape technique also work with such a large piece?
Thanks for these videos! They are so great. Question for you on this installation….could you do the same in the topsides? I have fixed ports with frames that I’d like to replace and do this way but of course those ports are sometimes partially in the water when the boat is heeled. Do you think this install technique would be suitable as well?