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aspiring sailor
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Discussion Starter #1
I am changing my deck mounted running lights; the old lights were "bedded" with about 1/2" of silicone. I've managed to get a lot of it off, but the last bit doesn't want to go. What is the best way to get this off? I've tried vinegar, IPA and scraping. . .
 

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Sea Slacker
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No chemical will help.
My own process for removing silicone is:
1) using a chisel on the largest amounts
2) using a knife (I have an old kitchen "steak" type knife with a relatively flexible blade) on what remains
3) using sandpaper on the surface to remove the "residue" (check by wiping some water on it - if water no longer "beads" or "pools" - silicone is finally gone).

While doing that, I keep cursing the PO and whoever was the first dumass that thought up the idea of using silicone as a sealant on a boat.

(Just had to rebed the dorade boxes and, you guessed it, more silicone)
 

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Sea Slacker
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Acetone helps
I used to think that :)

That said, it does help in some cases if silicone is applied over something like paint that can be dissolved by acetone - in which case silicone may somewhat come off with underlying material. This does not generally help on FRP.
 

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That said, it does help in some cases if silicone is applied over something like paint that can be dissolved by acetone - in which case silicone may somewhat come off with underlying material. This does not generally help on FRP.
Geez - guess the sink in my head must have been painted :)
 

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Telstar 28
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Unfortunately, the oil from the silicone is a pernicious contaminant on fiberglass and very difficult to get rid of. If you think you've gotten rid of it all—an easy way to check is to pour water over the surface.... if it beads at all, instead of wetting the surface, you failed.
 

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aspiring sailor
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Discussion Starter #9
Thanks all for the input, when it stops raining I'll be back at it. . .
 

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One thing that worked for me was the Interlux fiberglass solvent wash. It broke the silicone down (it became crumbly) where I could scrape and wipe it off. Had to use a lot of solvent, but it worked.

Also, I've seen a silicone remover at Ace hardware. It comes in a caulking gun tube, and it's not cheap, but could be worth a try.
 

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Super Moderator
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The only

The only chemicals, that would be readily commercially available, that are not recommended for long term use with silicone are Xylene and Toluene.

Silicone is highly resistant to Acetone and also to mineral spirits/stoddard solvent (which is basically WD-40). While over time mineral spirits/stoddard solvent may cause swelling to the surface of the silicone it will NOT remove silicone contamination from fiberglass or gelcoat. Just because you rubbed the visible residue from the surface does not mean it is not still silicone contaminated..

The only real cure for silicone contamination is wet sanding. Xylene and Toluene would need to be in contact with the gelcoat for a LONG time to remove any silicone and doing so may harm the substrate..

Trust me I have tried many tactics over the years and NOTHING removes the underlying contamination better than wet sanding.
 

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baDumbumbum
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If you aren't concerned with saving the paint, try brake cleaner. Methylene chloride, if you still find it, is the best silicone remover. For a safer chemical, 3M makes a spray remover; and their Prep Solvent 70 is used by auto painters to clean off residual silicone, supposedly with excellent results. YMMV.
 

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Tundra Down
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My old, weathered, white, textured, gelcoat deck has no objections either strcturally or visually in the prudent use of a stainless steel "tooth brush". It picks out the residual bits. In tough situations I use a mild wire brush in my portable electric drill. I just re-bedded all my deck hardware last week.

Tundral Down
 

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Methylene Chloride is a very nasty chemical and should not be used unless you're wearing a respirator and heavy gloves, full face mask... as it is skin absorbable and highly carcinogenic.

If you aren't concerned with saving the paint, try brake cleaner. Methylene chloride, if you still find it, is the best silicone remover. For a safer chemical, 3M makes a spray remover; and their Prep Solvent 70 is used by auto painters to clean off residual silicone, supposedly with excellent results. YMMV.
 

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Methylene Chloride is a very nasty chemical and should not be used unless you're wearing a respirator and heavy gloves, full face mask... as it is skin absorbable and highly carcinogenic.
It can also eat paint, was the active ingredient in many paint strippers before they removed it due to its cancer causing attributes as a carcinogen, and it can melt certain plastics including softening gelcoat if left on long enough to actually melt the silicone. In short duration, like Acetone, it will not harm the gelcoat much but if left on the surface long enough to soften the silicone you might also soften the gelcoat with it.

Remember you're not working on steel automotive panels or cast iron brake rotors and most hulls are not made of epoxy.

Methylene Chloride is often used to remove silicone conformal coatings on PC boards. In order for it to remove a 0.010 mil thickness it may take 15 minutes to an hour for it to soften the silicone enough for removal and this is submerged in a bath of it.


Here's an excerpt from a study done on removal of conformal coatings:


"As in the case of the polyurethane’s, the coated board is immersed in the solvent at room temperature and allowed to stand
until the silicone has dissolved or can be easily brushed off. The time required will vary with the solvent used, the type of silicone
coating, the coating thickness, and the amount of surface area exposed.

Typically, most coatings of 0.010 inch or less will be
removed in 15 minutes to one hour. Certain chemically-resistant silicones may require extended immersion for several hours. The
use of ultrasonics or agitation will reduce dissolving time.

After coating removal is complete, it is very important that the board be thoroughly washed in alcohol (isopropanol or methanol),
then rinsed in DI water and dried. A saturated cloth or cotton-tipped swab may be used for spot removal. Repeated applications
and brush may be necessary.

Some of the newer silicones will not come off with any form of chemical. Make sure you check with the manufacturer before
you use any chemicals on newer silicones.
"





On a boat you do not have the ability to submerse the deck for 15 + minutes and rags are not going to cut it. Marine based silicones are designed to be of the chemical resistant type and are generally more resistant to chemicals than PC board conformal coatings.
 

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fiestaMojo, if you are planning to replace the old lights with new ones, you probably don't need to be too concerned with trying to remove all traces of the old silicone.
If that is the case, then you may want to try using a wire wheel on a 4" hand grinder. I have used a steel one to successfully removing 5200 from gelcoat. However, if I were concerned with damaging the deck, I would use a softer bronze wheel.
 

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aspiring sailor
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Discussion Starter #20
Actually the WD-40 worked quite well at "loosening" up the old silicone, just a little scraping with a razor blade afterwards did the trick. Now, what should I use when mounting the new lights? I have a pair of Innovative Lighting LED navigation lights (got them for a good price), and a Perko-style stern light (the foam rubber gasket/brass mounting plate set up).
 
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