Is Marine Silicone any different? - SailNet Community
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post #1 of Old 04-02-2009 Thread Starter
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Is Marine Silicone any different?

I was looking at clear non-adhesive silicone sealant today. The "Marine grade" stuff is much more expensive than the "bathroom" grade at Home Depot. Is there a significant enough difference to pay the extra, or is it just a marketing gimmick?

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post #2 of Old 04-02-2009
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What are you using it for. Silicone-based sealants have very little good use on a boat, other than bedding lexan/acrylic glazing, covering the ends of cotter pins and being used on the bottom of dishware to make it non-skid.

Using it on deck hardware is really a bad idea, since all silicone sealants tend to leave behind contaminants that make resealing the area afterwards almost impossible.

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post #3 of Old 04-02-2009
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To answer your question, I don't know, but somehow I doubt they are different. I guess that is not helpful...

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post #4 of Old 04-02-2009
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Two major kinds of silicone sealants: those with acetic acid (vinegar), and those without. You want the kind without, as the acetic acid can really pit and corrode marine fittings. If you are sure this is a job for silicone (as SD says, it's right for very few boat jobs), use GE Silicone II Sealant, available at your local hardware store. Still about $6 a tube. GE Silicone I is acetic-based, so don't use that.

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post #5 of Old 04-03-2009
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learning these seemingly small facts is what makes this forum great. I just love picking up these tips! Now I just have think where I may have used the vinegar smelling silicone around the boat!!!! oops!

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The problem with the acetic acid-based silicone is that it tends to attack metals... because of the acid. Fortunately, acetic acid isn't all that aggressive an acid.

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post #7 of Old 04-03-2009
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i have a tube of this stuff on board as my general sealing/adhesive stuff ( also have 4200 ). it a liquid nails product, that is very clear when cured. it sets up pretty quick and is not hard to remove later. if i had to give it a 3m comparison i would say its a little weaker than 4200 but has better flexibility. i used it to seal the plex on my roof hatch, and you have to look to see it. i see it as my 4200 replacement when i dont want the white or want it clear.
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post #8 of Old 04-03-2009
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What about the hybreds?

This seems like a good thread to ask this... What about those sealants that are half silicon and half something else? It would seem that they have the same issue as silicon (contaminating fiberglass) but many people use lifecaulk and other hybreds.
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post #9 of Old 04-03-2009
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Spinlock specifically points out in their documentation that polysulphides and urethanes should NOT be used to bed their rope clutches; they want silicone to be used. Reasoning provided is that the polys will degrade the plastic materials? So, I will hope that I never have to rebed.

How do you clean the contaminant residue left behind to get a good seal when rebedding?
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post #10 of Old 04-03-2009
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Silicone

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Originally Posted by jason3317 View Post

How do you clean the contaminant residue left behind to get a good seal when rebedding?
You will need to sand it after removing as much as you can by hand. Tape off the areas you don't want sanded and then sand the contaminated area. Certain plastics can have the plasticizers leeched out of them over time from products like polysulfides. This leeching makes the brittle and more prone to failure. In these situations I would recommend Dow 795 as the Silicone of choice..


As Dog stated silicone has very, very few good uses on a boat. Certain plastics require it because they can be attacked by Polysulfides, Polyurethanes or Polyethers.

The problem with Silicone is that it nearly permanently contaminates a surface. Even when you think it is gone and you've rubbed it away it is still there. Simply use a spray bottle, like for ironing, and mist the surface it the water beads the surface is contaminated.

Silicone was and is designed to resist attack by most all chemicals. None of the commercially, body shop strength, removers are really all that safe for fiberglass and even they don't work all that well even on metal.

Once you've used silicone it will be very tough to get anything else will stick to where you had the silicone.

There are also MANY grades of silicone and it goes much deeper than just marine or bath tub. Acrylic hatches should only ever be sealed with Dow 795 or GE SG4000 as these are "structural grade" Silicone products. Bath tub silicone is not even rated as such and should not be used to seal ports or hatches as it is just not safe or prudent behavior.

If you are going to choose a Boat Life product stay away from the combo Life Seal product as you WILL get silicone contamination and choose Life Calk for general bedding uses unless certain plastics like Polycarbonate or Acrylic..

For those of us who have had to atually remove silicone contamination, for paint work, I can asure you the ONLY way to 100% get rid of Silicone contamination of gelcoat is to sand it off.. Just because you can't see it does not mean it is not there, trust me!!

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Last edited by Maine Sail; 04-03-2009 at 07:37 AM.
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