Letters 3M 5200, a Sticky Subject
I note a couple of errors in Jack Wilkin’s article on “Mounting Winches” that are important.
The first is small but important to note, that “Silicon” is a metal. What the author should have used was “silicone”. Perhaps just a typo but he used it twice. Secondly and much more important fact and generally not well known. 3M 5200 does indeed stick like crazy to fiberglass but not to metal. Specially Stainless Steel. I suggest Jack take two flat stainless items, or perhaps a stainless and an aluminum piece and bed them together. Leave them outside in the elements. In 6 to 12 months you will be able to separate them easily. Many yards suggest bedding deck hardware in 5200 as was my boat. In time I found virtually every part leaking. Stanchion bolts and bases, chainplates, everything was bedded in 5200 and leaked. Removal and rebedding was accomplished easily and rebedding with silicone has provided 12 years of waterproof use. The only thing that I know that silicone does not stick well to is acrylic. Nor should it be used below the waterline.
Good luck to Jack and Seattle Boat Works and to your fine magazine
Glen Read SV Nootka IP40/62 Shoreline WA
Geez, I’ll take the shot for the Silicon instead of Silicone faux
pas. Too obvious to notice. We forwarded your letter to Jack and here’s his response.
First, thank you for your feedback. Yes, of of course SILICON is a metal, it was a typo that got repeated. No one can argue with success and I am glad you have kept watertite. We do not recommend 5200 but, having said that, I have had it pull the gelcoat off a deck when removing deck hardware. Apparently in some cases, yours for example, it can also fail to seal. A possible reason that 5200 might have failed is that a primer was not used. 3M recommends its silicone only as a bedding sealant and says it has the lowest tensile strength of its Marine Sealants. I have had silicone fail with hardware that was subject to uneven or shock loads. One example was a spring line cleat with (2) bolts on a 50 foot ketch. It was mounted the first time with silicone and the bond let go. After that it was remounted with Life-calk. After 25 years it is still watertite. BoatLife rates Life-Calk as Excellent and Silicone as Satisfactory for Metal to Fiberglass.
(
http://boatlife.com/media/BoatLIFE_Catalog2010.pdf
Good sailing, Jack Wilken
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