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Old 16-06-2016, 17:15   #1
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Layer of silicon in the bilge?

I'm currently grinding and painting the shower bilge of my steel yacht. It's not in Trimble condition but will require the usual priming, painting and what not. I was wondering why I never hear of people adding a layer of silicon on top of the painted and prepped surface as another barrier so that no water makes its way through the paint and to the steel. There is a great deal here in Sydney on silicon at the moment so I could do it cheaply. Any ideas why this isn't a common practice.
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Old 16-06-2016, 19:31   #2
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Re: Layer of silicon in the bilge?

Silicone is fundamentally evil. Once you apply it the surface is permanently contaminated and nothing, not even new silicone will adhere anymore.

This isn't a huge issue at home because silicone sealant can last forever, or pretty close. But boats shift and move, which will quickly break the bead. At which point you can no longer fix it.
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Old 17-06-2016, 00:37   #3
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Re: Layer of silicon in the bilge?

And try getting a nice smooth, well bonded surface with the stuff.. It is hard enough when it is just a small bead. Trying to paint it on would be a disaster. Even if you did get it nicely painted on silicon isnt noted for its adhesion, so it would likely peel at some point, or let water in and trap it someplace.

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Old 17-06-2016, 01:08   #4
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Re: Layer of silicon in the bilge?

Black mold grows and thrives on silicon and is impossible to clean..
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Old 17-06-2016, 06:18   #5
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Re: Layer of silicon in the bilge?

Way back I was involved in some research in steel rebar for concrete. We were testing epoxy coatings. The result was if you could get a truly perfect seal, it was great. If there was even the slightest flaw that let water in, it was worse than no covering at all.


With silicone no way are you going to get that perfect seal and as others have suggested, there is no way to completely remove the silicone when the time comes to redo the bilge.
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Old 17-06-2016, 13:56   #6
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Re: Layer of silicon in the bilge?

Just go with pure vinyl paint. Perfect for bilge, under cabinets, etc.
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Old 17-06-2016, 17:27   #7
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Re: Layer of silicon in the bilge?

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Originally Posted by reed1v View Post
Just go with pure vinyl paint. Perfect for bilge, under cabinets, etc.
The better alternative would be a waterproof membrane paint. EmerClad or similar is readily available in Sydney hardware stores - just remember you are applying a membrane, NOT a paint. Roll it on with no pressure, multiple coats etc etc, you are building up a thick dimpled film.
If it is for the shower sump, I personally would prefer to use a smooth shower base and drainage sump to keep the soap scum out of the bilge.

Silicone or other membranes are good but have edges that let water under. Then they encourage corrosion and finally the membrane peels-off as a sheet.
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Old 17-06-2016, 17:36   #8
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Re: Layer of silicon in the bilge?

Clarification please

When you say 'silicon', what exactly are you referring too? What sort of application is this silicon ins cheap supply off? Are you referring to silicon in the tubes? Or some sort of brush on or spray silicon?
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Old 17-06-2016, 17:44   #9
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Re: Layer of silicon in the bilge?

Silicon is sand, the stuff they make electronic chips out of. Silicone is the stuff they put in boobs and sell as a crappy sealant. Yes, the latter is the spawn of the devil unless you like plastic tits and leaky boat.
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Old 17-06-2016, 18:40   #10
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Re: Layer of silicon in the bilge?

Quote:
Originally Posted by Herreshoff View Post
I'm currently grinding and painting the shower bilge of my steel yacht. It's not in Trimble condition but will require the usual priming, painting and what not. I was wondering why I never hear of people adding a layer of silicon on top of the painted and prepped surface as another barrier so that no water makes its way through the paint and to the steel. There is a great deal here in Sydney on silicon at the moment so I could do it cheaply. Any ideas why this isn't a common practice.
Thanks.


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Old 17-06-2016, 19:37   #11
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Re: Layer of silicon in the bilge?

Silicon can come in many forms and applications. Even on a boat silicon has its place. For example sealing plastic inspection hatches to plastic water tanks. Sika won't stay stuck and thus leaks. You can get silicon in liquid forms for adding to concrete, adding to paints etc. all sorts of applications.

But for what your wanting to do, and on a steel boat, my experience of wasting time with a number of recommendations, id recommend you skip all the magic recommendations and go with two coats or 2 pack red oxide, the 1 or 2 of 2 pack primer and then either a single coat of 2 pack top coat or alternatively a 'suitable' single pack designed to go over the 2 pack primer. E.g Norglass products are brilliant.

Don't waste time with anything else. This is what the origional manufacturers probably did and on the inside of my boat it's lasted more than 30 years. from now on, I'm going with this. I'd recommend you do the same. Slightly more expensive paint, extra time needed in mixing, but done once and it's done.
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Old 17-06-2016, 20:42   #12
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Re: Layer of silicon in the bilge?

I never allow silicon sealants on the boat. There are many much better adhesives and sealants for nearly every application.

Silicon (assuming you're referring to that crap people buy at the hardware store) has additives which make it generally acidic, will not adhere over a large area due to its high surface tension when dry and has no resistance to scratching. It also fails under peel when subjected to compression due to its high surface tension.

What you need to do is apply an epoxy coat. You can color them. Grit blast then apply following the manufacturers instructions. They have high hardness, they're tough and can be tailored to have a thermal expansion rate close to steel.

Silicon coating will also trap soap scum and grit and become a stinking moldy mess very quickly. Epoxy will not.

Epoxy coated steel is used extensively in industry to protect low cost steel vessels from almost any aggressive chemical.

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Old 18-06-2016, 01:02   #13
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Re: Layer of silicon in the bilge?

Having battled rust in the bilge of a steel boat for 29 years now I have come to the conclusion that unless you can sand or grit blast the two packs are a waste of effort and money.


I did a hull refit in 2012 and went from one end of the bilge to the other with pneumatic chisels and needle guns and recoated with epoxy and it is failing in numerous places.


I have used cement render with boiled linseed oil and white cement for a number of years and have found it to be just as effective as the epoxy coatings and I suspect in some places it has given better performance. I have taken to filling water traps with it and it seems to work fairly well.


I am now coating the bilge with waxoil made out of candles and engine oil. For the first batch I went with dissolving the wax with white spirits but have given up on that and now just heat the candle wax in a metal bucket and stir in the engine oil. It appears to do a good job of wetting the steel, can be reflowed using a hot air gun and will be readily removable with solvents should I wish to do so.


I went with the waxoil after reading about it on the forum. On pondering on it I remembered an oil company storage yard near the sea in south east Asia where they coated pipes in storage with waxy crude oil. It was filthy to handle the pipes but the storeman told us that over decades of experience this proved the most effective protection in the long term. Since nothing much else has been very effective I thought I would give it a tryout.
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