Polyurethane Glue

[Murray16764]

I made an attempt to reseat a fixed port on the roof of cabin of my Ben352 last summer. I used silicone adhesive/sealant, which was recommended by others. The repair didn't work and it started leaking again in a month. The port is a challenge as it has no frame or screws to hold it in place. It just sits in a depression on the fiberglass roof with about a 3/4 inch overlap. The port is made of plexiglass.

I was thinking of using polyurethane glue for the next attempt - specifically Gorilla Glue. I have used this on other projects and it works very well. The fact that it expands 3 to 4 times will work to advantage in that it will force all the air pockets out of the overlap and make a perfect seal, I think. Once the glue is set, than I can put a bead of silicone around the edge to finish. The Gorilla Glue company has confirmed that the glue will bond these materials.

My concern is that by boat repair book recommends not using polyurethane for this purpose - not reason was given. The only issue, and it is not minor, is that you only get one shot at it. If it does not work or goes wrong, you have a real big time mess on your hands.

Any thoughts out there?

Murray

 

[sailaway78]

What is recommended

What is recommended by the mfg. There is more than one type of silicone. The silicones are good sealants, but leave something to be desired in the area of adhesion. You also have two different materials to bond to. I would see what the mfg. recommends, and be sure to read the directions carefully. There are some other things available besides silicone you could also use. 3M 101 or Boat Live for example. There are several different opinions from members of this board concerning this subject. Check the mfg. recommendations and follow them. I wouldn't use something that you could never get apart without destroying the port or the boat.
Just as important as using the proper material, is following the directions for it.

 

[Ross]

Modern windshields are adhesive bonded on cars. That material is probably your best choice. Remember someday you might have to change the piece and you won't want to dismantle the boat to do it. I wouldn't choose to use any polyurethane not made for the job.

 

[Don S/V ILLusion]

Ross is correct.



Dow Corning 795...
is a structural silicone used to bed windows in commercial buildings and windshields on most cars. I used it to bed the frameless plexi windows 3 yrs ago and it's holding well. Bonus: it's really inexpensive and comes in several colors. You should be able to find it an an industrial building supplier.

Silicone, to my knowledge, is the only sealant that's compatible with acrylic.

If you decide to go with the Sika 295, be sure to use the primer as it won't stick without it. It's also very stiff to work with.

 

[Rick D]

Dow 795

I am currently having new opening and fixed ports made up and installed by a professional. He strictly uses DOW 795 as did Hunter when the boat was built.

 

[Dave Groshong]

Pompanette (Bomar) recommends GE Ultra Glaze

 

[Chuckbear]

I am currently having new opening and fixed ports made up and installed by a professional. He strictly uses DOW 795 as did Hunter when the boat was built.

We have used Dow 795 on Lexan and all types of Plexi on our own boat as well as many others I have worked on and NEVER had a leak or failure. Manufacturers that quit using it did so to save costs and had nothing to do with the quality of the product.

 

[caguy]

I am sold on a Butyl roof flashing sealer. Dries clear sticks well and maintains just the right resiliency. I will post a pict of the stuff when I get home.
I haven't used it on gel coat or plastic and would test it first.
What ever you go with wou will have a diificult time getting it to stick to the old surface where silicone was previously used. You may need to sand or scrape surface to get rid of silicone traces. Fresh silicone won't even b ond to cured silicone.
Good luck,

 

[Stu Jackson]

Just do NOT use

glue.

 

[Maine Sail]

Some points..

The Beneteau windows were originally installed with a structural silicone of some sort. Most companies use Dow 795 as it has a long and proven track record for this application. Polyurethanes & polysulfides should not be sued on certain plastics acrylic & Lexan are two of these plastics.

The problem with silicone is that NOTHING, not even a new bead of silicone, likes to stick to it and failures are likely if the surface is not fully prepped. ALL old silicone must have been removed with a light sanding as the last step. Always test the area with a fine mist of water. If water beads it is NOT clean and ready.

You need to use a flexible sealant for this application Gorilla Glue or any other polyurethane "foaming type" glue will not work as it will not flex and move with the deck.

Also when installing the window you really need to keep it off the fiberglass it sets in until cure. If you do not do this you will have no bead and you won't have enough thickness of silicone to flex and move. A penny or nickel placed at four points and taped to the underside of the glass to keep it in place just barely overlapping the fiberglass lip will allow a full cure and leave enough sealant to accommodate movement.

I would not advise the use of polyurethane glue, polyurethane adhesive sealants, butyl or polysulfides for this job as many of these products can harm the acrylic by leaching plasticizers out of the product over time.. Dow 795 or a similar product will be the best product for the job provided you prep and install it correctly. There needs to be sealant around the edge and under the glass for this to work. A bead around the edge only will quickly fail..

 

[sailingdog]

If the port is only held in place by sealant/adhesive, then that is one thing—but if the port has some fasteners through bolted, I would use a butyl rubber glazing tape to seal it.

 

[Salty]

I agree that the Dow Corning #795 is the way to go. I am looking to replace one of my windows and it was recommended.
http://www.drmarine.com/products.asp?cat=244

 

[Steve Dion]

I would also agree with the DOW 795. We did this a couple of years ago on a Bene 34 and the window is still intact and no longer leaking.

We completely removed the entire window (very difficult project) and then cleaned the entire area. We then put some silicone feet on the fiberglass to keep the window slightly raised so the 795 did not squeeze out when pressure was applied. Once the window was bedded we used sand bags to keep pressure on the window until the 795 cured.

I think you will find that Sika makes a comparable product, but I would stick with something that we know that works and works well.

 

[pvanv]

If it's compatible with the lens (is it acrylic or polycarbonate or tempered glass?), a durable choice would be 3M 5200 polyurethane anhesive sealant. Very permanent and quite strong.

 

[sailingdog]

Not a big fan of 5200. It's too strong an adhesive and causes problems when things need to be replaced later on.

If it's compatible with the lens (is it acrylic or polycarbonate or tempered glass?), a durable choice would be 3M 5200 polyurethane anhesive sealant. Very permanent and quite strong.

 

[dvantong]

Dow 795

Where can I buy this stuff?

 

[Ross]

Re: Dow 795

What Stuff?

 

[dvantong]

Dow 795

Dow 795

 

[Ross]

Re: Dow 795

Auto glass shop.

 

[Steve Dion]

You will find the Dow 795 at a contractors supply. It is not an auto glass product. This stuff is used to glaze windows into sky scrapers. Hunter also sells it. You may see prices from $7-10/tube. It also comes in several colors.

If you go to the Dow site, you can probably find a dealer in your area.

I believe that your port was originally glazed with one of the Sika products (not sure). Use the Dow product you will not be disappointed.