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Old 04-23-2017, 09:09 PM   #1
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Silicone or Butyl Tape for plastic ports.

I'm replacing the broken and crazed Gray Marine plastic opening ports on my boat. I'm replacing all of them starting with the one in my aft shower/head. That one had been replaced with a Beckson that was very similar to the others but not quite the same. When that one was replaced, the liner around the opening was broken. I have repaired the liner and will do some painting to make it all look nice. Everything I have read says use silicone to seal plastic. I was wondering if butyl tape might work well but do not want to damage the ports with an incompatible substance. If my ports were made of anything other than plastic I would not hesitate to use butyl tape. Have any of you used butyl tape in this application with success? Thanks for your input.

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Old 04-23-2017, 09:59 PM   #2
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Mr. t. IF you use RTV silicone you will NEVER get paint to stick. EVER!
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Old 04-23-2017, 11:40 PM   #3
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The butyl won't hurt the plastic, but butyl requires a lot of pressure to get it to flow out and seat properly. I use it where ever possible. I am not sure you could tighten down on the plastic enough without cracking it. I would rather not use silicon for the above mentioned reason, you can't get rid of it. I am going to use Sika 395 UV to bed my plexiglass windshield. You might look at it.
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Old 04-23-2017, 11:58 PM   #4
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I'm a diehard, unapologetic fan of butyl sealant but agree with Dave, this sounds like an ideal Sikaflex application.

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Old 04-24-2017, 10:04 PM   #5
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If I'm not mistaken the Sika Product is for mounting unframed portlights. This is not what I'm doing. After much research I'm going to use 3M white marine silicone for at least this first port. It was bedded in clear silicone (not the original installation). I'll see how this works for me and also take a very close look at what the originals were bedded in as I take them apart. I will be masking very carefully to keep silicone "creep" to a minimum. The silicone will be installed with just a snug fit until cured and then given a tighten to compress it much like with butyl only without thru bolting as in most butyl installations. We'll see if it works.

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Old 04-25-2017, 01:17 AM   #6
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Sikaflex(made by Sikkens) is a polyurethane adhesive sealant, comes in several variations. From reading posts,think 3M 5200, but I`m not sure. They make a silicone too, it`s good. And Cetol too. If you can use silicone you could probably use Sikaflex, without the "no paint" drawback, but if you need to remove it, eg failed experiment,silicone would be easier than Sikaflex, and it`s less messy to use,I usually tape up when using Sikaflex.
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