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Old 21-01-2023, 09:41   #16
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Re: Best goo for sealing hatch

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Originally Posted by mikereed100 View Post
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?
With many years of experience installing and resealing the various hatches and windows on this yacht and previous yachts, I can say that old sealant, silicone or otherwise, does not have to be chemically removed from the aluminum frames.

If the old sealant is scraped off new sealant will stick. It will stick to the bare aluminum. It will stick to the old sealant. Getting sealant to stick to the frame is not the problem. The problem is getting the sealant to stick to the plastic lens (usually acrylic). Acrylic has a high coefficient of expansion, (meaning it expands and contracts quite a lot) and it has a waxy finish which often releases from the sealants.

One of the best sealants is Dow 795, and follow the instructions closely for gap and thickness of the sealant bead.

Other approaches can be tried:
Recently our large (31"x31") bow hatch released from the frame after about three weeks. I had used 3M 4000 because that is all I could obtain at my location. This problem occurred out in the islands and we had a rough passage ahead of us. A loose bow hatch lens was not acceptable. We found that the sealant was still firmly attached to the frame all the way around. To reseal the lens we cleaned and sanded the edge of the lens (where the sealant would touch it), and, working frantically, applied a layer of super glue to the old sealant, then laid the lens on it. When I say we worked fast, I mean fast. I reckoned we had about 10 seconds to paint on the super glue and then put on the lens. We did it and it worked. The super glue stuck to both the existing sealant (like a gasket) and to the acrylic lens. The old 3M 4000 stuck to the frame. This hatch is still tight one year later.
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Old 22-01-2023, 10:25   #17
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Re: Best goo for sealing hatch

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Originally Posted by wingssail View Post
With many years of experience installing and resealing the various hatches and windows on this yacht and previous yachts, I can say that old sealant, silicone or otherwise, does not have to be chemically removed from the aluminum frames.

If the old sealant is scraped off new sealant will stick. It will stick to the bare aluminum. It will stick to the old sealant. Getting sealant to stick to the frame is not the problem. The problem is getting the sealant to stick to the plastic lens (usually acrylic).
Respectfully disagree with this. Nothing, including silicone, will stick to cured silicone. It may for a short time, but the bond will eventually fail.

Like you, I have been resealing windows and hatches for decades, but my experience has been quite different. When we bought our cat we re-glazed all 8 hatches with new acrylic. We removed the old acrylic, scraped the aluminum frames clean, wire brushed them and sanded them. We then bedded in the new acrylic with Dow 795. All was good for about 2 years, then the sealant started releasing from the aluminum frames. Over the years we resealed each hatch at least 3 times, using a different sealer each time. They would be dry from 1-2 years, then start leaking at the aluminum frame. I researched this a bit and learned that silicone cannot really be sanded off. Sandpaper just smears it around while removing the material underneath. I started using chemical removers and have not had to re-seal a hatch since then. A bottle of Goo Gone is so cheap and easy to use, why would you not take the extra couple of minutes to ensure a good bond?

This topic come up every couple of years or so. The complaint is often that a re-sealed hatch has started leaking again despite careful prep. The thing they all have is common is not having used a chemical silicone remover.
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Old 27-01-2023, 06:49   #18
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Re: Best goo for sealing hatch

I have 6 opening hatches with aluminum frames. At first, when hatches started to leak, I tried all kinds of stuff. What has worked the best is generic acrylic held in place with DC 795. In the tropical sun, the 795 will last longer than the lens. Use a very sharp blade to remove old caulk. Sand both the lens and the aluminum with about 100 grit sandpaper. Clean both sides with alcohol. Repeat several times until the rag is clean when you’re finished. Make sure you leave enough space around the new lens for a thick bead of caulk. 1/8” minimum on ALL sides. FRESH 795. Expired caulk will not hold and once took many months to set.

It’s possible that there’s a special acrylic that light be more UV resistant. But the local suppliers would want to sell a whole sheet. It was cheaper and easier to replace more frequently.
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Old 27-01-2023, 07:15   #19
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Re: Best goo for sealing hatch

Bonding plexiglass hatch panel to aluminum frame.

Dow 795

https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1
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Old 27-01-2023, 07:45   #20
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Re: Best goo for sealing hatch

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Originally Posted by mikereed100 View Post
Respectfully disagree with this. Nothing, including silicone, will stick to cured silicone. It may for a short time, but the bond will eventually fail.

Like you, I have been resealing windows and hatches for decades, but my experience has been quite different. When we bought our cat we re-glazed all 8 hatches with new acrylic. We removed the old acrylic, scraped the aluminum frames clean, wire brushed them and sanded them. We then bedded in the new acrylic with Dow 795. All was good for about 2 years, then the sealant started releasing from the aluminum frames. Over the years we resealed each hatch at least 3 times, using a different sealer each time. They would be dry from 1-2 years, then start leaking at the aluminum frame. I researched this a bit and learned that silicone cannot really be sanded off. Sandpaper just smears it around while removing the material underneath. I started using chemical removers and have not had to re-seal a hatch since then. A bottle of Goo Gone is so cheap and easy to use, why would you not take the extra couple of minutes to ensure a good bond?

This topic come up every couple of years or so. The complaint is often that a re-sealed hatch has started leaking again despite careful prep. The thing they all have is common is not having used a chemical silicone remover.
I agree and have a little bit of a chemistry warning.

First, everything mikereed says is true. Getting silicone to stick to non-porous previously siliconed surfaces that are simply mechanically cleaned will not be effective in generating truly long lasting joints. They will last long enough to get the customer out of the shop, however.

BUT... (again as mikereed suggests) despite what some people claim, cleaning it up is NOT terribly difficult. Just about any organic solvent will quickly and easily remove the residual "silicone oils" from non-porous surfaces that reduce the long term adhesion. A commercial mixed solvent (like Goo-Gone) or even isopropyl alcohol will do an excellent job.

There is however another "BUT" here... residual alcohol (like IPA) or ketones (like in Goo Gone or acetone) will inhibit the cure of at least some of the neutral cure silicones. You want to be 100% sure that all the solvent has flashed off before going ahead with the next step. If the surface you are working with is at all porous, you might want to let it sit for a couple hours to be sure.

The process is not rocket science, but there are details that need to be attended to. Because some of the details are not obvious, it is not unusual that people make up explanations for failures that have little to do with reality.

One of the little details that rarely gets mentioned from Dow technical literature: For uncoated, unanodized aluminum it is recommended that a primer be used for DOW795. If your hatch frame is NOT anodized, and you are having trouble, this could be the reason!
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Old 27-01-2023, 07:54   #21
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Re: Best goo for sealing hatch

"...One of the little details that rarely gets mentioned from Dow technical literature: For uncoated, un-anodized aluminum it is recommended that a primer be used for DOW795. If your hatch frame is NOT anodized, and you are having trouble, this could be the reason!....."

Good to know!!!
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Old 27-01-2023, 08:09   #22
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Re: Best goo for sealing hatch

Amen to the warnings about 5200. It is for permanent fixes only…if you try to remove it after curing, it will destroy whatever it touches.
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Old 27-01-2023, 08:27   #23
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Re: Best goo for sealing hatch

"If you try to remove it after curing, it will destroy whatever it touches."

IF it sticks, it usually sticks tenaciously. True enough. But if the joint fails, 5200 is no more difficult to remove than anything else. A sharp blade, followed by sanding. With the case of 5200 with polycarbonate or acrylic, the joint usually fails to stick.
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Old 27-01-2023, 08:35   #24
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Re: Best goo for sealing hatch

3M 5200 and 4200 both loose their bond with the aid of a heat gun.

"The heat gun is your friend..."
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Old 27-01-2023, 09:25   #25
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Re: Best goo for sealing hatch

The secret to good sealing is not to expect the sealant to act as the glue. They can if everything is perfect in the instillation, but this may not always be the case.


To get the perfect seal requires some time, that may not always be available, but should be aimed for when ever possible. Install the item in the normal way, using a little more sealant than you would normally use, then screw/bolt the item lightly into place. Allow the necessary time, days or weeks as may be for the sealant to cure.


Once cured, tighten the screws/bolts to the suitable tension. This way you are compressing the sealant as a gasket, so it does not require to "stick" to the items to seal.
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Old 27-01-2023, 11:36   #26
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Re: Best goo for sealing hatch

I've used and had good success with bedding ports using 3M RTV tape which is also used for bedding auto windows, as well. Mechanically abrade the fiberglass or aluminum frame & clean with alcohol to remove residue. Apply the RTV tape inboard of the outside edge of the glass or plexi/ acrylic lite about 1/8". Mask around the perimeter of the lite with painter tape. Set the lite in place and place the heaviest thing on the surface of the lite to compress the tape some weight to compress the RTV. remember, you've only got one shot at this. Seal perimeter edges w/DC 795. Works great!
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Old 27-01-2023, 11:48   #27
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Re: Best goo for sealing hatch

Put some 3M sealant/ caulk on my plexi in a plastic frame in 1990 and it held up well. Don’t have it anymore but when checking on West Marine’s site to try to jog my memory they do have a table that you may find useful. Flex Seal has worked for me with glass to metal including UV resistance. Only issues I had with the black 3 M product was it coming off on clothing.
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Old 27-01-2023, 17:13   #28
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Re: Best goo for sealing hatch

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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

See if you can find something like this where you live. It could be a different brand, but basically it is 'white Silastic', although while there 'shouldn't be any difference' I had more success sealing leaks with the 'Wet Area' edition!


https://www.selleys.com.au/products/...icone-sealant/


I used to have a large hatch on the sloping (about 45 degrees) front of my cabin, just over the vee berth. It was hinged to allow access to the deck should I need it.
The thing sealed perfectly around the part that opened and closed. But it leaked where it fitted into the deck, and it leaked around where the glass fitted into the frame of the lifting part.


I managed to stop the leak while it was raining, by smearing a little of the stuff onto each side of the leak with a finger and rubbing it in until it got sticky (even though water was still running 'over' the part I had smeared).


Then I squeezed some along the part that was leaking and with a wet finger, eased it over the leak until the leak sort of sat in a bit of a bubble behind it. A little while later after it had skinned, I carefully built up more until I had a decent sized glob of the stuff stopping the rather heavy rain coming in.


Later, when the sun came out, I scraped as much off as I could, although there was a cured layer that I had to clean off. From memory I used white vinegar. I could have used acetone, I can;t remember.


Because the repair 'while it was actually raining' had worked on both bits that had leaked, and because I did not want to replace the opening part of the hatch, and it would be a while before I had decent weather to remove and reseat/reseal the outer frame, I did the same thing again while it was not raining, but without the bubble of water behind it.


I also went outside and did exactly the same thing on the outside of the hatch.



That repair lasted the next couple of years and I forgot about doing anything to fix it.


On my next yacht I discovered leaking windows on my first wet trip after I bought it.
I used the same stuff and method to stop the rain 'while it was leaking', then cleaned it up and did a repeat on the inside and outside once the weather was suitable.


I used to assume that the Wet Area silicone was just a brand name thing to trick people into thinking there's a difference. But I've tried doing the same repair with ordinary silicone and it just balled up under my fingers. Maybe it was the way I held my mouth.


I've also never had success stopping leaks using Sika. No idea why. Again - it must be me . .
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Old 27-01-2023, 17:45   #29
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Re: Best goo for sealing hatch

I'm trying to absorb the above. What makes a silicone "neutral curing"? I do recognize the difference between hardware store "silicones" and the "real" stuff that smells like vinegar (actic acid) are the smelly ones all RTV's or is there yet a different distinction?


Thanks,


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Old 27-01-2023, 23:46   #30
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Re: Best goo for sealing hatch

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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.
There are silicone based adhesive/sealants that are used to seal and hold the glazing in multi-story buildings, they are incredibly strong and durable, however you don't find them at general hardware stores.
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