Why I HATE Silcone Sealant

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.

 

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

 

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.

 

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...

 

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

 

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

 

Silicones & Boats

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

 

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

Nice post Brian.

 

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

 

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.