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silicone  Bottom

  • anyone know the best type of silocone to seal ports?
    should they be unscrewed before applying?
  • For years I've been a big fan of Sikaflex, but of late Tom Haberman has really sold me on 3M 5200.

    --
    Southern Alberta and all over the damn place.
    *
    1983 SuperCat 19
    TriFoiler #23 "Unfair Advantage"
    Mystere 17
    H18 & Zygal (classic) Tornado - stolen and presumed destroyed by evil people. Very unpleasant story.
    Invitation and Mistral and Sunflower and windsurfers w/ Harken hydrofoils and god knows what else...
    --
  • pretty sure this is what i used, and it worked really well. I think tho that if you get to a marine supply store, they would have something that will work.
    https://i.imgur.com/nQSaqNe.jpg

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    1978 H18
    1983 H18 (some of it)
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  • 3M-5200 is an adhesive caulk commonly used in marine applications for through-hull and hardware sealing. It has very strong adhesive quality. 3M-4200 is just as good, but easier to remove when the time comes. Both are white in color and can be removed using Marine Debond, which is kind of a super Goof-Off solvent. I often use butyl rubber tape as a sealant where there is a lot of flex in the part. It is capable of stretching a lot before the seal is lost and is relatively easy to disassemble parts. Butyl marine tape can fill larger gaps. Silicone is probably good to use on your house or bathtub, but is not very durable or reliable on a boat.

    They no longer make contoured ports so it is likely that what you use for caulk will need to be thicker on the outer edges and thinner along the center-line of the hull. The 3M products would be ideal for that. Do not distort the port rim by screwing it tight before the caulk has set. The lid will not seat correctly if you screw down the rim, so be sure to support the outer edges with the 3M caulk and let it set before screwing it down.

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    Tom
    NACRA 5.7 (1984 Sail 181)
    Pennsylvania
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  • I have read many threads on this topic and all include the "DO NOT USE 5200" warning. 5200 is for bonding things which are to never come apart again (hull/deck joints). It is more glue than sealant.
    Quote3M-5200 is an adhesive caulk commonly used in marine applications for through-hull

    I pity the fool who has to remove the thru-hull in the future. There are better alternatives for below the water-line. Check Practical Sailor for advise on this.
    https://www.practical-sai…hanes-sulfides-silicones

    4200 is great stuff. So is sikaflex. I use clear silicone on the mast and butyl everywhere else.

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    Robert
    81' NACRA 5.2 "Chris's Flyer"
    Previously owned H18, Trac 14, G-Cat 5.0, H14T, H16, N5.0
    BYC, Mobile, AL
    --
  • Thanks - I'll look into 4200.

    And I'll repeat it again here: Domestic silicones suck. Completely useless on boats and a real PITA to clean off. I'd dismiss the whole family of silicone RTVs out of hand, but I've used enough automotive-gasket-maker RTVs (red, grey, black, etc.) to get that they have their place. I've just never conducted any experiments to see whether any of them are at all suitable for marine use.



    Edited by jonathan162 on Sep 10, 2021 - 05:29 PM.

    --
    Southern Alberta and all over the damn place.
    *
    1983 SuperCat 19
    TriFoiler #23 "Unfair Advantage"
    Mystere 17
    H18 & Zygal (classic) Tornado - stolen and presumed destroyed by evil people. Very unpleasant story.
    Invitation and Mistral and Sunflower and windsurfers w/ Harken hydrofoils and god knows what else...
    --
  • Anyone use the red rtf silicone?

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