Hi Goeff
Thanks for a rational post. Let me make a couple of points.
First you concussion about adhesion is somewhat wrong but I understand what you are saying. Adhesion is important as most sealants fail when they come loose from the surface they are sealing. This will allow moisture to seep in further causing release. You will see this when you remove a leaking fitting and see some parts come off easy while others stick very well. I have removed many fittings put down with 5200 that lifted the gel goat in some places while you could clearly see water stains in other areas that had let go of the surface. So a sealant must stick well to the surface. I think what you are talking about is the sealant strength or it ability to hold together, ie tensile strength. 5200 being very high on this scale butyl very low. So you want your sealant to adhere well although may not need a lot of strength.
The thing is most people working on boats need to understand is that there is no one sealant that will work in all applications. You have to use the correct sealant in the correct application. I get frustrated when someone makes the blanket statement that one sealant is better than others and the only one to use or that another should never be used at all. When I hear statements like that I know the person does not have a clear understanding of how sealants work.
Having been in the marine industry for 40 years building and repairing boats I have a large history to draw from and have learned what works where. This has been through trial and error on my boats and other peoples boats. 35 years ago everyone thought butyl was the best thing going, 20 years ago we all thought 5200 was, we have since learned. I have had the rare opportunity to survey boats I personally built 20 years before, very educational to say the least. (And yes I did make mistakes)
There are those out there that simply refuse to understand that silicone does have a place in boats and when used correctly will outperform most other sealants. It will remain flexible far longer than most other sealants, it has some of the best UV resistant of the marine sealants, it is high temperature resistance (Ever take the temp of an aluminum fitting on a hot summer day?) and most importantly it is one of the few sealants that will stick to plastics for the reasons I stated before. These are facts not opinions based of years of testing. The contamination argument is a myth and it is no worse than any other sealant other than paint will not stick to it so it makes it more noticeable as you cannot paint over the film. Cleaning takes the same care as with any other sealant when uncured and with the correct solvent no harder.
I am happy to continue a discussion on this subject but not if someone is just going to respond “You should never use sillycone” those folks clearly have made up their minds and that is fine, I am trying to help educate those that are open to understanding.
Capt. Wayne Canning, AMS
www.projectboatzen.com
