Electrolytic action on aluminum spars
I'm in the process of painting the aluminum mast, boom and cross trees on a 1978 Islander 28. I've removed all the standing rigging & other hardware and sanded down to bare metal which after 30 years is still in excellent condition but for some slight surface corrosion on the boom around some of the steel fittings. I believe this is the result of electrolytic action and I'm looking for advice to stop it recurring. I guess I can coat screws and pop rivets with silicone but what about other areas where steel touches aluminum? Is there a recommended insulating material, an insulating paint perhaps or perhaps just more silcone? Apart from this one question I am ready to finish the project as soon as we have the next couple of Seattle days that are dry and over 60 Fahrenheit. Thanks in advance, advice much appreciated.
Using something like TefGel or LanoCote is probably better than using a silicone sealant. If the pieces are larger, say, like the base of a mounting plate or line clutch, you can use the thin plastic from the side of a translucent milk jug as a galvanic isolation washer, in conjunction with the LanoCote or TefGel.
I refurbished my corroded 62ft mast last year.
Don't use steel brushs or something to clean the aluminum. You will rub in tiny steel parts which will make your mast blossom again for no apparent reason.
Use etch primer prior applying the primer and AWL Grip. The etch primer will turn brown if applied correctly. Remove it if it does not and start again. Coat the etch primer with two-compound primer as early as possible to prevent separating.
Get rid of the steel rivets or screws wheresoever possible. Use MONEL rivets (Ni/Cu) instead. They are more expensive but it's worth it. Be careful - the load capacity of MONEL rivets is not as high as of stainless steel rivets.
If you have to use steel screws or rivets (e.g. top of mast track and points of reefing heights) insulate them with LanoCote.
RECKMANN Germany recommends "Wollwachs" (Lanolin) which is basically LanoCote. You get it as "Adeps lanae" in a good drugstore (at least in Germany) It's much cheaper. 150ml Adeps Lanae will cost you round about 4 EUR which will last for probably all the masts you will ever own (I replaced all 400 rivets and screws in my mast and the container is still full to the brim).
Concerning the material to insulate steel and aluminum opinions differ. There are some pastes to prevent corrosion. A surveyor and rigger told me that Sikaflex is the best bet you can get. But I was afraid of squeesing out the insulation when torquing the fittings. So I sticked to the more traditional way of using a special rubber tiles German snowplows have attached to edge of their shovels which appeared to work well (my mast is 30 years old).
Don't use rubber discs underneath winches. It's too soft. I used 4mm GRP tiles instead.
If you feel like having a look at some pics I will upload some of them.
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