Silicone caulk vs.3M5200

[jimnmad]

I have been looking through the search topics and don't seem to see anyone using silicone caulks as a sealant on say a centerboard trunk. It would seem to me to be a good alternative to 5200 in that it seems like it should seal well and still be somewhat removable as long as you aren't looking to take advantage of it's adhesive properties. I can only assume by the lack of recommendations of silicone's use that it must not work well in boat construction. What is it's downfall?

[Ken Hutchins]

Don't put anything silicone anywhere near anything you may want to paint ANYTIME in the future.

[Del Lansing]

Just a note, every tube I've read (I haven't read _every_tube) say's, "not recommended for use below the waterline." So for a centerboard trunk cap, where you may need to uncap and unjam a stuck board, OK. But why buy a tube for such a small bit of usage?

[Bob Smalser]

Paint the wood with an oil-based primer and paint before using poly sealants and the seal is most durable but is removable at the expense of that coat of paint. Scuff the paint with Scotchbrite before applying.

I use silicone on equipment gaskets regularly, but it doesn't have near the sticking power of poly.

[gary porter]

Silicone sealant is used on items like deck plates ports etc where you are just sealing the item not adhereing it. You can buy small tubes of 5200 or 4200 which is a slight compromise and is easier to remove. What is said above is true for the painting so mask off the area and clean it up then remove the masking. Paint won't stick to silicone.
Gary

[rrowlands]

Ditto the comment about NEVER using silicone on any boat which might be painted or varnished.

I'd recomend a good bedding compound which wil alow disassembly when and if te time comes.

[Steve Miller]

I was the Dap Industrial Rep for 9 years. Sold a lot of silicone. No bathtub caulk on my boats. We used to joke that silicone will stay flexible and be warranted to be flexible for 50 years but no one ever said it would stick for 50 years! I hate the stuff. There are only a few companies that actually make silicone. Most of it is just relabeled. Last I looked I think just 3 actual silicone makers in the world.

Life Caulk does have a new product out called Lifeseal that is a combo material for sealing plastic and some sufaces that 5200 or 4200 won't.
Combo of marine silicone and polyurethane. I tried it on my old Neptune 16 portlites last summer and its still going strong. Tools nicely.

But even 4200 will pull paint and veneer if you are clumsy in removing cleats and things to repaint. Ask me how I know...

[Steve Miller]

As far as below the waterline, silicone is the glue of choice to build aquariums. Special formula that does not give off fish killing nasties while curing. Stuff seals the glass for years below the waterline. Other than the paint not sticking - ever - anywhere near silicone, I think the issue is that its too flexible, too soft to be a good construction sealant like 5200 etc. Its more of a caulk. It will peel right off some slick surfaces too. Remember that a caulk and a sealant are not the same thing. Boats need sealants. Bathtubs and windows need caulk.

Reminds me of the time a buyer (female) wanted to know why she should continue to purchase our silicone when it was causing such problems with the breast implants. I told her that they did not use bathtub caulk in the implants. She continued to buy. That's all I'll say on that topic.

[NormMessinger]

Our local Ace Hardware stocke about 750,000 different kinds of caulks and sealants. (Yeah yeah, I know you've told me a million times to stop exagerating.) Some are silicon based, unpaintable, some which look much the same coming out of the tube are paintable. I confess to having used some of the latter to bed four cleats on Prairie Islander--could wait on mail order and didn't want to buy a big tube for a little job. Anyway, I wonder why the stuff won't work just fine. I may not live long enough to find out, so there.

Regarding silicon sealant that smells like acetic acid when it cures which perhaps is what is being discussed above: The nav lights on the wing tips of my airplane and the vertilons on the wings are glued on with the stuff. The airplane is 20 years old this year, cruises at 170 MPH. Oh well. If they fall off sometime in the next 30 years at least they are outboard of the prop.

[jimnmad]

Thanks for all the input. I think the thing I was looking for is that it is too soft and will peel right off. I knew there was a good reason for not using silicone, I just needed help thinking of it. Thanks again