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Garry R
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Post by Garry R » Wed May 25, 2005 10:26 am

I am about to do the finishing varnish on a wooden mast then I will be refitting the hardware. Do you attach the hardware with a light coat of wet varnish underneath so that you get a good seal and to stop biting the metal through the previous varnish or do you just "go dry"? Also do you give metal work eg the hounds etc a light varnish after finishing?

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Ed
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Post by Ed » Wed May 25, 2005 10:57 am

Personally....

I put last coat of varnish on and then smear a marine silicon sealant under the fitting to stop water getting underneath too much. Don't really see why you couldn't use a light coat of varnish though....it would do much the same thing.

don't think that I would bother to put a coat of varnish on the metalwork though....it will just start to come off and look rather untidy.

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JimC
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Post by JimC » Thu May 26, 2005 12:03 am

Varnish on metal fittings looks like hell: avoid!

johnconradlee
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Post by johnconradlee » Thu May 26, 2005 2:22 am

Varnish on fittings looks great for a time but looks bad after, kind of how modern brass letter boxes etc go when the protective laquer get's scratched, only not as bad as it was tarnished before. However on the occasions when I have varnished over things (I always tried to go around things but when you have 15 feet of mast to go and what you've done is running.....) I've always argued "I'm presearving the metal", besides it's high enough off the deck for no one to see. I always put the fittings back on when the last coat is quite tacky so it'll still bed down and seal. I'm not sure if that's the best way though, I think silicone type stuff might be better as the varnish tends to crack around the fitting if there is the slightest movement.
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Ian Malcolm
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Post by Ian Malcolm » Thu May 26, 2005 4:06 am

The problem with silicone sealant is silicone contamination of nearby painted or varnished surfaces. This will give you hell when you want to repaint/revarnish (look up 'fish-eyes') or even re-seal the joint. It is also a pretty poor sealant and tends to fail by seperating from the surfaces its between and trapping a film of water under the fitting. (Acid free electronics EHT insulation grade silicone is much superior, but even that can fail if there is any surface contamination and it costs the earth for a small small tube - worth it for sealing critical cables and connectors though)

Personally I like Butyl mastic. No adhesive properties worth mentioning but if the fitting is properly mechanically fastened it will stay soft, rubbery and waterproof for years. Talk to a shop that repairs caravans to find the stuff. Shelf life once opened is usually measured in years!

For *most* uses NON-SILICONE marine mastics are OK, but UNLESS YOU NEED A STRUCTURAL ADHESIVE like 3M 5200 or 4200, they are grossly over priced and dont really offer many benefits. Once you've opened them (or even before) the shelf life is a joke even if kept foil wrapped in the fridge.

For underwater bedding of things like my keelband, lately I've been using black fiberous bitumastic roof & gutter mastic. It used to be available in a tube from B&Q but the've dropped if in favor of acrylic mastics so I bought a tub from Wickes. Disadvantages - So slow setting you wont be able to varnish over it the same season. Advantages - It stays soft and sticky enough to move with any dings that dent the keelband and for any crack to self heal for at least five years.

If you are fastening Aluminium or light alloy fittings to wood they *must* be well bedded on good mastic or even better, Duralac. (search for "poultice corrosion" and you'll learn why).

I've learnt to dip all screws in varnish before fastening them (to prevent water wicking down the thread into the wood) and I confess to bedding small lightly loaded fittings with varnish. If the fitting is going to be under a lot os strain with shock loadings such that you are considering through bolting it you should really consider cutting a rubber gasket for it *AND* for its backing plate and bedding both faces of both gaskets with butyl mastic. You can use 1mm neoprene sheet, but I usually cheapskate it with old inner tube rubber. My mainsheet block/jammer fastenings were a 3 times a season maintenance item before I did this, now it went ten years without any trouble and when I finally took it off last year (to move it 2" aft) the varnish under the gasket was still sound after I'd scraped off the dried mastic. Needless to say, I rebedded it the same way.

The remaining method is bedding on Epoxy. Read the West Systems literature if you want to go this route. *NOT* appropriate for most wooden boats.
Ian Malcolm. London, ENGLAND. (FORUM REPLY PREFERRED)
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