My new-to-me swing keel (1977) will be on a mooring in salt water (Plymouth MA Harbor) for three months. I'm dropping and refinishing the keel, should I add zinc anodes after sandblasting and before any coatings? I think I saw a reference to someone who attached a zinc anode to their winch cable and threw it over the side when not sailing?
Anodes
- Thread starter mrudman850
- Start date
What you are talking about (throwing zinc over the side) is called a 'remote' anode and it happens to be the least expensive and easiest to maintain option.
Many of us who have fully refinished our keels with epoxy can't stand the idea of drilling a hole into what we just made waterproof, so that starts the quest to protect underwater metal without drilling holes into stuff.
If you do an effective coating of epoxy to the freshly blasted cast iron, then epoxy fairing, followed by epoxy primer paint and then bottom paint; water should never touch the metal again. Without the electrolyte galvanic corrosion cannot occur. There is a question as to how effective the remote anode actually is because it is electrically connected to the keel winch and the keel cable that is stainless steel and a relatively poor conductor... Well, I see it this way; my keel was in super bad shape after years of neglect with NO protection what so ever. Since I was able to save it and now it is epoxy protected I'm not worried at all that it will be harmed even without a zinc. When I do use my remote anode I will monitor it to see if it the zinc is actually being eaten away, no harm in trying.
BTW, you are on the right path with sand-blasting first. Just be sure to get it home and wash it down with acetone and apply epoxy immediately, moisture in the air works fast to rust cast iron. Pay special attention to the keel pin. Get the stainless bushing installed if you can, but at the very least soak it with epoxy. It would be a shame to refinish the keel and then have rust start right away in the keel pin hole where there is exposed cast iron.
Many of us who have fully refinished our keels with epoxy can't stand the idea of drilling a hole into what we just made waterproof, so that starts the quest to protect underwater metal without drilling holes into stuff.
If you do an effective coating of epoxy to the freshly blasted cast iron, then epoxy fairing, followed by epoxy primer paint and then bottom paint; water should never touch the metal again. Without the electrolyte galvanic corrosion cannot occur. There is a question as to how effective the remote anode actually is because it is electrically connected to the keel winch and the keel cable that is stainless steel and a relatively poor conductor... Well, I see it this way; my keel was in super bad shape after years of neglect with NO protection what so ever. Since I was able to save it and now it is epoxy protected I'm not worried at all that it will be harmed even without a zinc. When I do use my remote anode I will monitor it to see if it the zinc is actually being eaten away, no harm in trying.
BTW, you are on the right path with sand-blasting first. Just be sure to get it home and wash it down with acetone and apply epoxy immediately, moisture in the air works fast to rust cast iron. Pay special attention to the keel pin. Get the stainless bushing installed if you can, but at the very least soak it with epoxy. It would be a shame to refinish the keel and then have rust start right away in the keel pin hole where there is exposed cast iron.
Not only is the length and resistance of the electrical path a issue, but the sheer mass of the piece of metal to be protected is probably too great for any but the largest anodes to do any real good.
Your real concern is rust anyway, and an anode will have no effect on that.
Your real concern is rust anyway, and an anode will have no effect on that.
Was planning on immediately spraying cold galvanizing paint after sandblasting, then epoxy....thoughts on this approach? Thanks.
The cold galv spray is just a band-aide approach if you don't have time to immediately apply epoxy. Personally I think its a waste and could potentially hinder the ability of epoxy and fairing to stick (but I don't the chemistry of the paint so I can't be sure). The best way is to plan ahead, coordinate with your sand blaster and be able to pick up your keel as soon as it is finished. Don't let it sit overnight, especially outdoors. The acetone wash will displace any surface moisture and rinse off the dust. If you can't apply epoxy right away try rolling on a one quart kit of Interlux Interprotect 2000 (epoxy barrier coat)... it bonds tenaciously to metal and epoxy filler/fairing will stick to very well. The biggest enemy is moisture in the air if its a humid day. If you lived in AZ during the super dry 100 degree days you'd have less to worry about.
That's the best possible scenario... acetone rinse and hit with epoxy right away. Some tips I learned from my experience;
- I tried laying the keel flat on two heavy saw bucks, you're better off hanging the keel from a cherry picker if you can, or just from anything you have; that way you can get at both sides.
- Be careful with the epoxy, I had a batch kick off and boil in the plastic contained because I didn't work fast enough. Pro tip - pour it into a flat paint roller tray after mixing, it won't warm up too fast.
- using the fast cure hardener is fine, just use the shallow roller pan and roll it quick. If someone talks you into using a slow cure epoxy then it will be harder to 'hot coat'.
- I found that 10 to 12 pumps of resin was what it took to completely roll one side. Start with 8 pumps and se how far that goes.
- Buy just two quality epoxy rollers and some cheap chip brushes, you only need them for the first two coats. Everything after that is done with spreaders and the pink Bondo Brand spreaders from Home Depot are cheap and actually very good.
- Your first two coats are the most important, these are the 'sealing' coats and need to be applied un-thickened. You want to 'hot-coat' them, meaning roll the first coat and when it 'kicks off' (becomes tacky but not cured) then roll on the second coat. This gives a chemical bond which is stronger than a mechanical bond and you don't have to sand between coats!
- The third coat you also want to 'hot coat'. You can allow the second coat to get firm, so basically your fingernail can press into it but don't let it sit overnight. This 3rd coat you want to add some filler like colloidal silica or micro fibers (not low density fairing filler). Use the bondo spreader to apply to damaged areas, low spots, holes, etc. Its ok to work in small batches as long as you are in the 'hot coat' window. Work the bondo spreader to get the smoothest surface you can but it need not be perfect.
- It helps to add grey or white tint to the epoxy, I prefer grey. The bottle is $16 but goes a long way. It adds the element of a visual indicator so when you start fairing you don't sand off too much material.
At this point you've applied two coats of un-thickened resin which is your true epoxy 'barrier coat' that is waterproof, plus the thickened epoxy to fill and smooth any rough areas or damage. You've 'hot coated' giving you a stronger chemical bond and avoided sanding between coats. Let this cure at least overnight, but now you can let it sit for as long as you like before you get back to it with no worries about rust. When you do get to the next step, sand with 80 grit on a belt sander or orbital to get the rough shape and then you can apply low density fairing filler.
+1 for sandblast and epoxy, do it once while you have it out and never deal with rust and corrosion again (at least on the keel 
)
)Fantastic information! Can I hope that when I remove the keel I'll find it was already epoxied and faired! Thanks folks!