When is "100% Silicone" not "100% Silicone"? The manufacturers of portlights recommend "100% Silicone" for installation. I can go to a marine supply store and get "100% Silcone" for $18-$22 per tube. Home Depot sells "100% Silicone" for $7 per tube. The Home Depot stuff doesn't address U/V protection specifically, but it does say that it's "Sun Proof". Can they (Home Depot) be believed?
Types of Silicon??
- Thread starter AllenF
- Start date
If the application is for portlights, you can't go wrong with Dow Corning 795. Its available on line for a price close to the Home Depot pricing. However the DC795 is truly an exterior application specific material used for outdoor structural window glazing. And it is 100% silicone polymer. Some of the other silicones sold at the big box stores are blends (silicone/acrylic latex) so they can be painted. They claim to have 35-45 years of service, but who knows. The 100 % silicones (RTV) I have purchased there seem to be fine for indoor use. One thing I don't like about them is when they cure, they give off acetic acid (vinegar smell) which can corrode adjacent metals. DC795 is a non acid curing chemistry. In the case of your portlights, the lowest cost silicone may not be your best choice.
Look on-line for the correct application specific deal.
It's hard to believe that there is something that 4200 or 5200 won't stick to, but acrylic is one. Silicone actually is the correct the correct sealant, and 795 is the best. The Home Depot stuff will work, but 795 will work better. Make sure to mask around the contact area, the stuff is a b***** to get off.
Your local glass shop will likely have DOW795 for a similar price. Check the expiration date, it is only good for one year before use.
3M4200 is incompatible with Acrylic, according to the 3M website. Same for most of their adhesives, excepting the 3200 silicon based item.
http://solutions.3m.com/wps/portal/...pair/GeneralBoatRepairs/SealantAdhesiveGuide/
I've used 795 to attach acrylic to a hatch frame but not aluminum to fiberglass. I thought 795 was specifically for bonding a plastic or glass to a frame?
- Jul 21, 2013
- 333
Silicone has gotten a bad reputation.. heres why.... its not because its a bad product, but its because so many people dont know there are different types of silicone just as there are 3M brands (4000, 4000uv, 4200, 5200 ect.), and they use the wrong type.... knowing what product to use for the application and how to prep and apply it is all that is needed for success...
The thought process is that Applying sealer from a tube seems so easy that even the simplest of the lazy people should be able to squirt sealer out of a tube and goop/smear it on to seal out the water, so why cant I?...
Then they all too often head down to their autoparts store or home improvement center and get something that says "silicone", and probably also says rtv somewhere on it, then attempt to use it without knowledge of the product or the proper preparation of the surface... and they screw it up.
When they have to clean it up so they can redo it, its a real pain in the a**, and instead of realizing the technique/lack of knowledge/prep they used was the problem, they clean it all up and go to the more expensive 3M brand of sealers... and in an attempt to not have to do a clean up again, and to get it sealed this time, they have taken what they learned in their first attempt, maybe asked a couple questions from someone who knows about the product, and they go forth and make a sucessful repair with the second product.
and then blame the previous product because it didnt work...
If they would have taken the care the first time like they did the second time, there would have been no need for the second time....
This happens all the time and so they complain about the product, but will never admit their lack of knowledge fueled the failed attempt....
Also, there is so much warning about using 3m5200, because its considered permanent and is worse than silicone to remove... very adhesive...
But used correctly, it can make a permanent seal. In my world, that is what i want, permanent.. there is no need to remove and reseal every 8-10 years of it isnt leaking... and if you have the tools and know how, 5200 is not permanent...
My point is, if you have knowledge of the product and how to use it, whatever it is, you will have sucess, but if you think its so easy that even a caveman could do it and you think you already know all you need to know about it, you are on the road to failure.....
Dow 795 silicone is an excellent product... other types can be used in some applications, but 795 covers them all except for engine or pump gaskets. It will glue it all together so it can never be serviced... use rtv on the engine/pumps and 795 on the hull/hardware/fittings...
cl is right. You have to use the right tool for the job.
Butyl tape is perfect for sealing deck hardware and chainplates.
Adhesives shouldn't be used for sealing.
Dow 795 is great for sealing fixed portlights.
Beckson recommends silicone for their ports and it is the only place I have used silicone on our boat (I have 8 Beckson ports).
BoatUS has a good primer on the proper use of sealants and adhesives, but they may not have "discovered" butyl tape yet!
5200 is relatively permanent, think hard before you use it.
Butyl tape is perfect for sealing deck hardware and chainplates.
Adhesives shouldn't be used for sealing.
Dow 795 is great for sealing fixed portlights.
Beckson recommends silicone for their ports and it is the only place I have used silicone on our boat (I have 8 Beckson ports).
BoatUS has a good primer on the proper use of sealants and adhesives, but they may not have "discovered" butyl tape yet!
5200 is relatively permanent, think hard before you use it.
The reason silicone gets a bad rap is because of silicone contamination. Nothing on a boat is "permanent" thus it will eventually need to be redone. Trying to get anything to stick where silicone had been requires judicious prep work because it gets into the gelcoat pores and is damn near impossible to remove all traces of because it is resistant to most any chemical that would be safe for the gelcoat for removal.
For well over 4 years I have been working with two excellent labs to develop a silicone remover that is safe for gelcoat and LPU paints. Many that claim to be safe for gelcoat cause premature crazing, softening and color changes to the gelcoat over time. Thousands of dollars in research & testing has failed to deliver a silicone remover worth selling. Anyone who tells you silicone contamination of gelcoat is nothing to worry about is simply ill-informed.
The best trick, to know whether the surface is ready for bedding, is to use a misting bottle of water. If there is any water beading on the surface, after cleaning the silicone, it is still contaminated and future seals will fail sooner than they should. If the water does not sheet off the surface the surface is still contaminated with silicone. There is a reason we use silicone spatula's, cookware, bakery molds, muffin tins etc. and that is because nothing likes to stick to silicone. Getting the surface 100% clean CAN BE DONE but it entails far more work than most boat owners would ever believe is necessary.
If you have plastic Beckson ports use Dow 795 or similar. There are places where silicone should be used but be 100% sure to prep the surface and get it 110% clean before installing the next set of ports. I had a good customer just last week, whom I had just installed an autopilot for, ask me if I did port replacements. "Sorry Meg not on Beckson's." She had Beckson ports and 3 out of the 4 were leaking from a failed factory seal of silicone.
I simply won't be the one to bill her an obscene sum of money for the "proper" job as the hours required, to do it right, are really insulting. The sheer number of hours entailed in PROPERLY prepping the surface for the new ports can get really crazy and I won't be the one to do that for a good customer. The catch 22 is I will only do a job the right way thus not worth insulting the customer because they have no idea what it really entails..........
For well over 4 years I have been working with two excellent labs to develop a silicone remover that is safe for gelcoat and LPU paints. Many that claim to be safe for gelcoat cause premature crazing, softening and color changes to the gelcoat over time. Thousands of dollars in research & testing has failed to deliver a silicone remover worth selling. Anyone who tells you silicone contamination of gelcoat is nothing to worry about is simply ill-informed.
The best trick, to know whether the surface is ready for bedding, is to use a misting bottle of water. If there is any water beading on the surface, after cleaning the silicone, it is still contaminated and future seals will fail sooner than they should. If the water does not sheet off the surface the surface is still contaminated with silicone. There is a reason we use silicone spatula's, cookware, bakery molds, muffin tins etc. and that is because nothing likes to stick to silicone. Getting the surface 100% clean CAN BE DONE but it entails far more work than most boat owners would ever believe is necessary.
If you have plastic Beckson ports use Dow 795 or similar. There are places where silicone should be used but be 100% sure to prep the surface and get it 110% clean before installing the next set of ports. I had a good customer just last week, whom I had just installed an autopilot for, ask me if I did port replacements. "Sorry Meg not on Beckson's." She had Beckson ports and 3 out of the 4 were leaking from a failed factory seal of silicone.
I simply won't be the one to bill her an obscene sum of money for the "proper" job as the hours required, to do it right, are really insulting. The sheer number of hours entailed in PROPERLY prepping the surface for the new ports can get really crazy and I won't be the one to do that for a good customer. The catch 22 is I will only do a job the right way thus not worth insulting the customer because they have no idea what it really entails..........
And im sure it wasnt a product failure, but the workmanship of the uninformed trainee they had doing the install....
And i will agree that it is not the best product for most applications and should never be used in some applications...
Always know the product and its limitations, and know what proper prep is for using it...
Sabre Yachts has veteran employees many of whom been there longer than the owners of the company and they are anything but "uninformed trainees". Everything in the marine environment has a life cycle and even silcone joints don't last forever. Come live a day in my world and tell me silicone in a marine environment does not ever fail and that these failures are always due to "uninformed trainees".....
Ir can be discussed/argued forever... and i will agree that no product lasts forever, nor should it be expected to..
And no matter how big or well qualified any given company is as a whole, there are always the trainees that are attempting to learn to keep the company going/growing and some just dont make it.
And i dont know for sure that it was a trainee that bedded the ports any more thay you are sure it was one of their most qualified personell, and neither do i know how old the boat is or how long the ports have been bedded or how long its been leaking since they were bedded.
I also dont know if the silicone bedding on those particular ports is crumbly or still firmly set as it should be, but i have seen many time where a silicone bedded port/window/hatch was leaking and just a small tightening of the fastner will seal it up again... too much and it can warp the frame and make it leak worse...
As for living a day of your life and seeing what you see and dealing with what you have to deal with, im sure its very different but not so much worse than the problems I need to deal with everyday as a result of someone elses poor decision making. You are just doing it standing on your head in a tighter space and having to carry your tools farther to the jobsite.
And sometimes i have to do a little bit of all of that too...
If either of our jobs were simple, we could just have our secretaries do it while we went sailing... ;-)