Best goo for sealing hatch

[nmccubbin]

We have a leaky hatch
Plexiglass set in an aluminum frame, with leak between the glass and frame
We replaced glass after 20 years with Goiot glass and goo provided by them
That has been great for 6 years, but a couple of years ago one was damaged and replaced with locally sourced plexiglass and Sikaflex sealant
It started leaking, so we cut the goo Silaflex pit and sealed with 5200
It has not stuck at all

We installed the 5200 on a very hot day in strong sun (we are at 8north)
Could that cause our problem?

What is the best goo for such a project?
We cannot source the goo used by Goiot

[SailingHarmonie]

Well, you were sucked into the mystic of 5200. You have heard how it sticks so well. So many people say it is good for everything. Except it is NOT. It is specifically NOT recommended for use with plastics. Like polycarbonate lenses for hatches. So it is not a surprise that it failed. This is one of those products that should require a license to use, so many people use it in places it has no place being used.

You say you used previously "Sikaflex." This means nothing. Sikaflex is a brandname that covers of dozens of different products, a few of which would be suitable, and most of which would absolutely NOT. A 6 year life before failure would clearly indicate it was NOT the right one to use.

Best "goo" for this is either Dow 795 or GE 2002 in whatever color suites your fancy. These are both neutral cure silicones. They are used to glue windows into high rise buildings, so yes, they work. Essentially identical products, whichever you can get locally will work. You will find them more likely in the building supply serving commercial builders than in marine stores. Follow the directions EXACTLY. Clean ALL traces of the old sealant off the hatch frame and lens. All of it. Seriously. ALL of it.

Be neat, be careful. Follow directions.

Both of these silicone products have strict expiration dates. Be 100% sure that the product you buy is NOT expired, even a "little".

[nmccubbin]

Thank you for a very informative comment. Our glass is not polycarbonate, but is some generic plastic provided by an “expert” in Panama
Will your comments still apply?
The Sikaflex I used was 291, which has been great for multiple other projects not involving windows
I will try to source the products you recommend

[Sailor Sailor]

I used GE SCS2000 on my acrylic/plexiglass replacements. Seems to work fine. I replaced all the gaskets at the same time.

[MicHughV]

I can tell you from hard earned experience that 5200 is not the product to use here...

...as above....use the GE SCS2000 or similar recommended goop as recommended above ..if you can get it...not sure that these products can be found at your local Home Depot....may have to try Amazon....

[SailingHarmonie]

Originally Posted by nmccubbin

Thank you for a very informative comment. Our glass is not polycarbonate, but is some generic plastic provided by an “expert” in Panama
Will your comments still apply?
The Sikaflex I used was 291, which has been great for multiple other projects not involving windows
I will try to source the products you recommend

Polycarbonate == Lexan
Acrylic == Plexiglass

Acrylic is far more likely to be a local "generic" option, and for hatch lenses, acrylic is actually the better choice. Neither option for material changes the recommendations for sealant.

Quoated from the Sikaflex 291 techncial data sheet:

Sikaflex®-291 must not be used to seal plastics that are prone to stress cracking (e.g. PMMA, PC, etc.).

PMMA == poly methyl methacrylate == plexiglass
PC == polycarbonate

So yeah, wrong stuff. It is also not UV stable. which is why it is recommended for INTERIOR uses. So using it on a transparent plastic facing the sun is doubly bad.

It is a single part polyurethane, just like 5200. It is not a sealant, it is a GLUE. It really should not be used as bedding compound, unless you have a special hatred for the next person who needs to work on that part.

[Bowdrie]

Sika does make a product for your application, it's 295 UV.
They have an extensive PDF on proper prep and the various amounts of clearance and bead sizes to allow for expansion/contraction depending upon the size of the panel.

[Capt Clark]

I have found that the Sika 295 UV works MUCH better when the primer is used. Quite expensive stuff but seems worth it if going the Sika route.

[mikereed100]

Unfortunately, most, if not all, manufacturers use a silicone when they install the glazing. This means that nothing will stick to the aluminum or the glazing until ALL the silicone is removed from both. Scraping and sanding are not enough, you must use a chemical remover. That bears repeating. You MUST use a chemical silicone remover. If you do not the hatch will eventually leak. I have used several and find that Goo Gone works as well as any and is cheap and readily available.

Once you are absolutely sure you have all the silicone off you have several options to seal the glazing to the aluminum including all the products mentioned in previous posts. Having used them all, my preference is for Dow 795 as it is cheap, easy to use, does not require an expensive primer like the Sika products and has great adhesion and elongation.

Did I mention you must use a chemical silicone remover first?

[Cheechako]

Originally Posted by nmccubbin

We have a leaky hatch
Plexiglass set in an aluminum frame, with leak between the glass and frame
We replaced glass after 20 years with Goiot glass and goo provided by them
That has been great for 6 years, but a couple of years ago one was damaged and replaced with locally sourced plexiglass and Sikaflex sealant
It started leaking, so we cut the goo Silaflex pit and sealed with 5200
It has not stuck at all

We installed the 5200 on a very hot day in strong sun (we are at 8north)
Could that cause our problem?

What is the best goo for such a project?
We cannot source the goo used by Goiot

I love 5200 but my experience using it when it's hot out is it fills with bubbles making it a bit spongy. I guess the bubbles must be outgassing and the goo sets up too fast. I sealed chainplates freshly in Trinidad and that happened. It looked a bit like foam when cutting it out to redo it.

If I were doing that I would get architectural window sealant. I think it's partially silicone but its very good and what holds big windows in skyscrapers in some instances.

[wholybee]

Sikaflex needs a primer to seal to acrylic or polycarbonate.
Dow 795 works better and does not need the primer. 795 is a silicone product.

[CaptTom]

When I replaced the plexiglass in an overhead hatch, the supplier recommended a product called "RTV." So far it's worked great. At any rate, it's probably worth going to a place which does this kind of work (typically, a glass place) and ask what they use. They'll probably sell it to you right there, and may even have a technician around who can explain how to prep the surface and use the product.

Anyway, that's what I did.

[SailingHarmonie]

Originally Posted by Cheechako

I love 5200 but my experience using it when it's hot out is it fills with bubbles making it a bit spongy. I guess the bubbles must be outgassing and the goo sets up too fast. I sealed chainplates freshly in Trinidad and that happened. It looked a bit like foam when cutting it out to redo it.

If I were doing that I would get architectural window sealant. I think it's partially silicone but its very good and what holds big windows in skyscrapers in some instances.

OK, repeat after me everybody: 5200 is NOT suitable for plastics. Ever. Period. Plastics like acrylic and polycarbonate. 5200 is just evil stuff. Even the poster here who "loves it" has had to redo seals made with it. Just dumb.

5200 is suitable for glueing on a keel, and little else. I'd NEVER buy a boat from somebody who says they 'love 5200." Because they will have used it in places is should never have been used.

As was already listed in the thread above, Dow 795 or GE 2002. Both are architectural window sealants. Just do that.

[SailingHarmonie]

Originally Posted by mikereed100

Unfortunately, most, if not all, manufacturers use a silicone when they install the glazing.

Because... it is the only stuff that WORKS!

[mikereed100]

Originally Posted by SailingHarmonie

Because... it is the only stuff that WORKS!

If that were true we would not be having this discussion. We should be clear about what kind of silicone we are talking about here. I suspect that many manufacturers use RTV to bed their glazing, which is a step up from some hardware store silicones, but still more suited to sealing bathtubs as it lacks adhesion and UV resistance. An architectural grade silicone, like Dow 795, has much better adhesion, UV resistance and 50% elongation, so it can handle the expansion and contractions of the glazing in it's frame.