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Old 05-02-2024, 11:43   #1
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Sealant for underwater lights. Primer?

I am installing underwater lights. They appear to be Acrylic, but not positive. The instructions just specify "sealant of your choice."

I obviously only want to do this once, and a failure will require a haul out. I am leaning toward 3m4200 over UV4000 because UV exposure should be minimal. Not so much by water by the shading from the curved hull. Both are listed as good for underwater through hull fittings.

But perhaps more important is the use of a primer. Being what seems to be Acrylic, should I, and if so what? I have spent all morning searching 3m documents, and while they say primer is required for some applications, they are silent as to what. One document said "See your distributor for appropriate primer." Of course, 3m has hundreds of different primers, mostly also silent on usage.
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Old 07-02-2024, 00:08   #2
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Re: Sealant for underwater lights. Primer?

I wish I could remember what sealant I used on the lightning earth strips on my yacht because I would have done a lot of research to pick the best.

I just did a google and there are a lot to pick from if you can believe their claims.(I probably used a Sika product)

mgMarineFlex high performance adhesive sealant can be used on boats, pools and spas, where you need a waterproof seal or bond, even under water* It can be applied and will cure under water – no need to drain your pool or spa.
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Old 07-02-2024, 02:06   #3
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Re: Sealant for underwater lights. Primer?

I would go for a aquarium silicone.
Something like this
Loctite Clear Silicone Waterproof Sealant.
Salt water and fresh water compatible.
Suitable for continuos water emersion.
Designed to stick to glass without primer so Acrylic will be fine.
Easy to remove without damage when the time comes.
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sealant, water

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