Why I HATE Silcone Sealant

[brian eiland]

this appeared in an online publication of SailWorld...too good to pass up, Brian


Many of the yukkiest, most pointless, timewasting activities in boat building and repair are all down to the misuse of silicon sealants. Generally if there is a leak some handyman type will try and fix it with this awful stuff. It is absolutely fine in bathrooms and houses but it just does not belong on boats. Why?

You can't paint it.

You can't sand it.

It doesn't stick well enough to be structural or to stop boat type leaks in its own right

It doesn't stick poorly enough to be easily removed.

When the thinners from paints hit it they spread its unpaintability to nearby areas which it hasn't contacted directly. YOu can the wash and sand to try and get rid of the residue and it just spreads it over the whole area so that the paint bubbles in an intermittent sort of way.

The only place it works is underneath fittings that are bolted or screwed to the boat - but ONLY on boats that will never be painted - even fibreglass boats may be painted one day - so what boats could they be?


Sikaflex, yes, yes, yes. - .. .
Use a polyurethane sealer like sikaflex. It can be sanded, painted and it doesn't really cost much more. It also seals gaps in a structural way - so if the bits move relative to each other it will still keep on working.

In fact you can glue a whole boat together with sikaflex - not that I'd recommend it - epoxy does a better job in most cases - but there are places...

Disclaimer - if I sound bitter it's because of bitter experience. I worked as a professional boat painter and varnisher over several years - silicone sealant was the #1 reason for having to redo work that we thought was finished.

About the author:
Michael Storer supplies Wooden and Plywood Boat Plans for Amateur Boatbuilders. They specialise in Light, Elegant, High Performance, and Simple Construction. You can buy his plans with Detailed Step by Step Instructions by going to his website (http://www.storerboatplans.com/index.html?nid=41427)

[PAR]

I've run into this many times and it's a pisser for sure. A quick trick I've found that works is to seal the stinking buggers where they lie with shellac. It takes paint and clear coats and will lock down the damn things, that seem to get many feet away from the place the first bead was applied.

[masalai]

Does it burn out? - with flame or acid - :D (similar treatment may work with silicone breast implants - similar misuse of a product)

[yipster]

The only place it works is underneath fittings that are bolted or screwed to the boat
used it again under a pulpit only becouse it was laying around but the old kit told me it does not even work properly underneath fittings that are bolted or screwed to the boat

[Jimbo1490]

I run into the same problem on airplanes all the time. Absolutely despise the stuff. The owner saves himself $25 on a tube of proper sealant only to squander 4 or 5 hours removing it from around ONE WINDOW a couple of years later! What a deal!:rolleyes: And why remove it? The leak has returned:D

[Fanie]

Silicone actually is a fantastic product, but really not for working on fiberglass or joining panels good grief !

Silicone is quite nice to form a rubber seal with, ie like for a port hole that can be opened. The structure gets applied with an even strip of the silicone and the window part can be covered by ie vaseline so the silicone does not stick to it. Close the port and wait for silicone to dry out some. It makes for a perfect fit rubber seal ;)

Silicone has to be removed mechanically, elbow grease. Mostly chemical resist and can withstand high temperatures - used widely to seal leaking exhaust flanges, so my guess is you'r going to burn the boat out before the silicone gives :D

[masalai]

That is what I was implying :D:D:D:D - get the owner to do it...

[Landlubber]

masalai,

Yes my friend, silicone can easily be burned out of the boat. One of the easiest ways is to let off a flare in the bilge, the resulting fire is sure to remove all the bloody silicone that some dumbwit has inserted within a few minutes. Just love your thoughts!

[masalai]

It's not a matter of thinking inside or even outside the box but "OVER THE TOP", and to have a reputation as a communist fish thrower helps in the "Ahhh, Now I understand" the logic :D :D Its a part of being entertaining and keeping them on their toes? - - and shitting some people off.....

[Meanz Beanz]

I use it in some applications where it has advantages, for example the deck beam seals on my catamaran. If I use Sika I would never be able to get the boat apart again, its actually quite a job with the silicon sealant that I use. I have found that the adhesive quality varies quite a bit between brands, silicon ain't silicon. Much prefer Sika if the job is permanent. I was once told that the secret to getting a good seal with silicone on deck fittings was to apply the sealant, fit the bolts, settle the fitting to within 1mm or so of the surface and then let it dry. Once dry tighten it down and trim.


Box? There is a box? :D

[kach22i]

I know that Silcone sucks, it will not even stick to dried Silcone very well. The guys at the hardware store sell it, but often ask customers what they are intending to use it for and often tell people just to use caulk.

I have not heard of Sikaflex before. I will be looking for it and may use it on my hovercraft repairs and modifications if need be.

Sikaflex
http://www.sikaindustry.com/ipd-ma-products

Lots of different products in the link.

Which one would you guys use on fiberglass boats?
http://www.sikaindustry.com/ipd-sikaflex291-cartridge-us.jpg

[Meanz Beanz]

It depends on the adhesive strength required, I think that 295UV is up the top end of the range. Slow cure is stronger from memory. The chandlery that I use stocks 290DC, 291, 291T & 295UV. Its a very similar product to the stuff that they stick modern auto windscreens in with. Some Oz boat manufacturers use it to attach windows to F/G production boats with no fastenings. Be very sure that you want what ever it is stuck permanently as the big problem with this stuff is getting the fitting back up if you need to. Practice a bit before you go for a bigger job, turps clean up but it can be very messy and it sticks to everything in sight if you are not careful.

Sika belongs in the hall of fame, one of those products that actually works!

[Landlubber]

3M 5200 is another very good product, same as the Sika story.

(For some strange reason though, Sika users get the stuff from arsehole to ear hole on a regular occurrence, 3M users seem to get more on the job and in the right place.)

[Meanz Beanz]

:D LOL, Using Sika cleanly is a skill! Not sure if that says more about the users or the product. I have not seen the 3M stuff, will look out for it.

Cheers

[Landlubber]

Meanz Beanz,

No mate it is definately not a skill associated with the product, even the unskilled manage to get it all over the place!

[kach22i]

While building a from scratch plastic RC hovercraft model I've been using a lot of E-6000, GOOP and Seal-All, talk about messy.

At least the E-6000 can be rolled or rubbed off your fingers.

[Meanz Beanz]

Sika comes off in the shower..... after a week or so :D

[CDK]

What I'm missing in this discussion is the use of a primer like Sika 206G+P. This liquid dries in 30 min. to a thin film by evaporating its aggressive and toxic solvent. Other Sikaflex sealants, but also silicone, adhere to the film with unbelievable strength. In fact, if the surfaces are pulled apart with enough force, the sealant will tear somewhere in the middle.
For materials like anodized aluminium or glass, Sika has an activator liquid that contains no polymer, just the solvent, that must be applied before the primer.

[Meanz Beanz]

You know when I started using Sika I can never remember a primer being offered and since then I have never used one but I have always had excellent results. I must give it a go, hard to imagine that the stuff can stick better but hey...

[Landlubber]

Yeah the primers work well, but on teak decking I always use Everdure, it is an epoxy fungicide primer, it is the best!

[Landlubber]

Everdure is a NZ product, was made by Epiglass till bought out by International Paints.

[brian eiland]

Here is a VERY informative contribution to this subject from another forum,
Brian

Gentlemen:

Although, in general, I do agree with what has been posted (Acetoxy based silicones—the type that is evidenced by the vinegar like odor during the cure) , you are leaving out what I call, a hybrid form of silicones that do have some wonderful properties and will out perform any of the polyurethanes in some very select applications.

These silicone adhesives or caulking compounds (Alkoxy or Oxime based silicones), are 100 % non-corrosive and use moisture as a cure mechanism (similar to many polyurethanes and polysulphides), but have not made its way into the general use marine market for various reasons. I consider them an undiscovered but vital tool for our work that can be used in many applications such as bonding stainless steel to FRP substrates without fasteners, bonding glass and acrylic windows to a FRP substrate without fasteners, sealing aluminum and SS fabrications when you need a superior bond but want a much softer durometer sealant ( movement between two pieces is inevitable and but a seal must be maintained), and certain other application where heat may be a factor ( polyurethanes soften quickly above 140F). Like the common silicone, paint does not adhere well, BUT they many clean up very nicely with common mineral spirits when uncured. Many can also be used (and are preferred) in electrical potting & sealing applications application when epoxies are not applicable.

Another important point that needs to understood when using any of the common polyurethanes ( 3M 5200, Silkaflex , etc) is that although they are quite strong for “gluing” things together (FRP and wood for example) , in many cases, relying on the “glue joint” for many applications, is only skin deep.. What I am referring to is whether the bond breaks "cohesively" or "adhesively"—big difference and can be very important--- a typical example would be 3M 5200 squirted onto a piece of smooth or polished stainless steel. Left to cure, it will then peel off like a band-aid.. Its adhesive properties are minimum compared to its cohesiveness on many substrates.. On the other hand, a product like GE 4000 Ultra glaze will not de-bond, but only let go cohesively-- the bond is stronger than the product itself. Kinda like a good wood glue—The wood breaks before the bond fails.

Some common applications where you might consider the use of a silicone product will be the bonding of acrylics & glass, SS, and aluminum where mechanical fasteners cannot be used. We also use Ultra-glaze 4000 exclusively as a sealing agent ( like a pipe dope) for the assembly of larger brass piping used in salt or fresh water applications -- in our work we cannot afford even the slightest weep,seep or "sweat" from a typical fitting or hose connection.

Again, I am not here to disagree with “Silicone has no place aboard a boat”, only to expand the knowledge on what the right type of silicone can offer.


Just a “Marine Nut Lookin’ In”

Tony

[Meanz Beanz]

Yeah the primers work well, but on teak decking I always use Everdure, it is an epoxy fungicide primer, it is the best!

Yeah I love the stuff, its another "Hall of Fame" product IMO.

Nice post Brian.

[kach22i]

Just an FYI, more comments on this topic by hovercraft builders in the link below.

Link:
http://www.hoverclubofamerica.org/forum/index.php?showtopic=1483

[Kaptin-Jer]

The first coat of awl grip I put on my boat had nasty crawls all over. It was the first time I ran into that problem. It took about two weeks of detective work, but I finally realized that a year ago I replaced the toe rails and a "friend" who is a roofer gave me 4 large sausages of sealant to use as bedding. Free seemed a lot cheaper than the cost of 5200. The sealant was silicone and a year later I was fighting the contaminate. Eventually I won, but the cost of additional Awl Grip and the additional time on the hard made the 5200 seem very cheep.