The cast iron swing keel on my Chrysler 26 starts to rust in a very short time no matter what kind of primer I put on. Would it work if I ground down the keel to bare metal and applied epoxy resin covered with a primer and then the bottom paint.
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Try this
Get the keel down to bare metal. Apply Petit 6980 rust inhibitor. This is good stuff and a quart may get you about two coats. The purpose for this is to stop rust from forming, which can happen even after epoxy is applied. Following that apply several coats of either Petit or Inter Lux epoxy barrier coat, the same same stuff you put onto fiberglass after sanding it down to the fibergalss or gel coat. The purpose for the epoxy barier coat is that it is an excellent water barier. If it keeps water out of fibergalss, it will keep water from damaging your iron. Secondly, the epoxy coating prevents the copper in your anti fouling paint from attacking your keel as well. If you then only use abaltive anti-fouling paint, you may never need to re-do your keel again. Only touch up the anti-fouling every two years or so.
Get the keel down to bare metal. Apply Petit 6980 rust inhibitor. This is good stuff and a quart may get you about two coats. The purpose for this is to stop rust from forming, which can happen even after epoxy is applied. Following that apply several coats of either Petit or Inter Lux epoxy barrier coat, the same same stuff you put onto fiberglass after sanding it down to the fibergalss or gel coat. The purpose for the epoxy barier coat is that it is an excellent water barier. If it keeps water out of fibergalss, it will keep water from damaging your iron. Secondly, the epoxy coating prevents the copper in your anti fouling paint from attacking your keel as well. If you then only use abaltive anti-fouling paint, you may never need to re-do your keel again. Only touch up the anti-fouling every two years or so.
Sandblast
You might want to see if you can get someone with an industrial sandblaster to sandblast the keel rather than grinding. We have a friend who has a business carving gravestones. It took him just over an hour to sandblast ours on both sides. He also had a crane on his truck to move the keel and turn it over. The only problem was convincing him that he should be paid.
You might want to see if you can get someone with an industrial sandblaster to sandblast the keel rather than grinding. We have a friend who has a business carving gravestones. It took him just over an hour to sandblast ours on both sides. He also had a crane on his truck to move the keel and turn it over. The only problem was convincing him that he should be paid.
No matter what you do
your cast iron keel is going to rust. Something will nick the coating, rust will start and undermine the ocating and one day a big chunk of it wuill fall off to reval a sheet of rust beneath. You just have to keep at it every year. Sorry. Been there, done that. And that. And that.
your cast iron keel is going to rust. Something will nick the coating, rust will start and undermine the ocating and one day a big chunk of it wuill fall off to reval a sheet of rust beneath. You just have to keep at it every year. Sorry. Been there, done that. And that. And that.
yeah im afraid the last guy it right
its a continual problem. petitt paints has a system for exposed metal. clean up the metal. coat it with aporduct called os-pho- its and acid wash the kills the rust. then prine with 3 part petet metal primer then red vinal undercoater. this is a red or orange coat of vinal that makes a great barrier. then paint with a good bottom paint. 2 to three years in florida.
its a continual problem. petitt paints has a system for exposed metal. clean up the metal. coat it with aporduct called os-pho- its and acid wash the kills the rust. then prine with 3 part petet metal primer then red vinal undercoater. this is a red or orange coat of vinal that makes a great barrier. then paint with a good bottom paint. 2 to three years in florida.
Thanks but why can't I
Do all the prep that Ed Allen recommended and instead of finishing with the bottom paint cover the keel with fiberglass cloth and resin and encapsulate the iron, then the bottom paint. No oxygen to the iron, no rust, Like Rust Oleam does to rusted metal in the open air.
Do all the prep that Ed Allen recommended and instead of finishing with the bottom paint cover the keel with fiberglass cloth and resin and encapsulate the iron, then the bottom paint. No oxygen to the iron, no rust, Like Rust Oleam does to rusted metal in the open air.
It will crack in the trunk when raised
When you raise up the keel, the edge that meets the bottom of the boat may be pressed too hard against the bottom of the boat and will crack your wonderful fiberglass job. This is easy to do with a winch that lifts 500 pounds with just one arm. Same will happen to just a epoxy barrier coat, but easier to repair. Also, the forward part of the keel as the keel drops down goes into its own space which will rub against the sides of the keel cracking whatever fiberglass coatings are there. And again, easier repair if just an epoxy barrier coat. And, of course, like everyone else, you can occassionally hit inderwater objects like submarines, although more likely just rocks.
When you raise up the keel, the edge that meets the bottom of the boat may be pressed too hard against the bottom of the boat and will crack your wonderful fiberglass job. This is easy to do with a winch that lifts 500 pounds with just one arm. Same will happen to just a epoxy barrier coat, but easier to repair. Also, the forward part of the keel as the keel drops down goes into its own space which will rub against the sides of the keel cracking whatever fiberglass coatings are there. And again, easier repair if just an epoxy barrier coat. And, of course, like everyone else, you can occassionally hit inderwater objects like submarines, although more likely just rocks.
Galvanize .. a more permanent solution
Why not have your swing keel galvanized? .. it would not be much more expence, and you've already done the hard work of removing it to grind and epoxy. I'm sure you could find a plater to give a good thick hot-dip layer.
Why not have your swing keel galvanized? .. it would not be much more expence, and you've already done the hard work of removing it to grind and epoxy. I'm sure you could find a plater to give a good thick hot-dip layer.
Not Sure its Possible
If you are planning to galvanize over the epoxy, I don't think it can be done.
If you are planning to galvanize over the epoxy, I don't think it can be done.
Sacrificial keel
Sacrificial anodes are zinc, and thats what galvanizing is, so it will tend to dissolve if in the water some time. If galvanizing were good underwater, you would see galvanized keels, outboard motors, thru-hull fittings, etc. Its used on trailers that are in the air most of their life, and thats not foolproof. I had a towell against a beam where my boat rubbed, and when I removed it after half a year, the galvanizing was gone. Sandblasting will clean up the keel, but it won't eliminate corrosion. Some moisture emerges from the metal itself, which is one reason primers never seem completely effective, especially with a porous metal like cast iron. Porous? Yes, remember seasoning that cast iron skillet so it would absorb some grease and work better? Thats why Pettit's Rustlok is better that primer. The Achilles heel of fiberglass keels is that there is a pivot hole that prevents total coverage. That and the fact that fiberglass is not as waterproof as we think. Some form of barrier coat would be better than fglass, or perhaps a combination.
Sacrificial anodes are zinc, and thats what galvanizing is, so it will tend to dissolve if in the water some time. If galvanizing were good underwater, you would see galvanized keels, outboard motors, thru-hull fittings, etc. Its used on trailers that are in the air most of their life, and thats not foolproof. I had a towell against a beam where my boat rubbed, and when I removed it after half a year, the galvanizing was gone. Sandblasting will clean up the keel, but it won't eliminate corrosion. Some moisture emerges from the metal itself, which is one reason primers never seem completely effective, especially with a porous metal like cast iron. Porous? Yes, remember seasoning that cast iron skillet so it would absorb some grease and work better? Thats why Pettit's Rustlok is better that primer. The Achilles heel of fiberglass keels is that there is a pivot hole that prevents total coverage. That and the fact that fiberglass is not as waterproof as we think. Some form of barrier coat would be better than fglass, or perhaps a combination.
lets look at all this
the ideas are well thought out. but the only thing that works is isolating the keel form the water. the glassing it over idea is expensive and will last a while but. when you glass it over it probably wont fit the boat anymore. and it will crack and leak just like the fixed keels do. the petitt system uses the red vinal undercoater as a barrier coat. when you use it once youll understand why it works better than most other coatings. but you have to stop the rust first. kill the rust. prime the metal paint with vinal then bottom paint will work in florida better than anything else we have tried on a lot of boats! the vinal is very thick almost like a rubber coating that is very impact resistant too! check with your local dealer and get the brosures from pettit and see what you think.
the ideas are well thought out. but the only thing that works is isolating the keel form the water. the glassing it over idea is expensive and will last a while but. when you glass it over it probably wont fit the boat anymore. and it will crack and leak just like the fixed keels do. the petitt system uses the red vinal undercoater as a barrier coat. when you use it once youll understand why it works better than most other coatings. but you have to stop the rust first. kill the rust. prime the metal paint with vinal then bottom paint will work in florida better than anything else we have tried on a lot of boats! the vinal is very thick almost like a rubber coating that is very impact resistant too! check with your local dealer and get the brosures from pettit and see what you think.
oh another thought.
Remember you got to get the bottom paint isolated from the steel. two different metals and it wont stay painted long.
Remember you got to get the bottom paint isolated from the steel. two different metals and it wont stay painted long.
Tried Glass
I filled the rust cavities on my Mac 23 keel with epoxy and then covered it all with fiberglass about 18 months ago. While lifting it back into the boat, I damaged the glass, which I repaired. I suspect, like someone said earlier, it will rust beneath the glass. The only question is how long it will take. There was no problem with clearance. I doubt that the glass layer added more than 1/10" to the keel thickness. It is questionable whether it is even worthwhile. I figured that the corroded keel would affect my speed very little since the keel surface area is small compared to the rest of the boat. However, I thought it might prevent lee way since the pits would induce turbulence. As best I can tell it made no difference on either count. Probably the best thing to do is to try to put on some type of coating which will reduce further corrosion.
I filled the rust cavities on my Mac 23 keel with epoxy and then covered it all with fiberglass about 18 months ago. While lifting it back into the boat, I damaged the glass, which I repaired. I suspect, like someone said earlier, it will rust beneath the glass. The only question is how long it will take. There was no problem with clearance. I doubt that the glass layer added more than 1/10" to the keel thickness. It is questionable whether it is even worthwhile. I figured that the corroded keel would affect my speed very little since the keel surface area is small compared to the rest of the boat. However, I thought it might prevent lee way since the pits would induce turbulence. As best I can tell it made no difference on either count. Probably the best thing to do is to try to put on some type of coating which will reduce further corrosion.
Guess what - it is now rusty
If you did your repair 18 months ago - I guarantee that your cast iron keel started to rust again 18 months ago (assuming you didn't seal the surface as you ground or sandblasted as you mentioned). You must seal the surface immediately. Just as soon as you have a shiny section you have to seal it. Moisture in the air instantly starts the rusting process.
If you did your repair 18 months ago - I guarantee that your cast iron keel started to rust again 18 months ago (assuming you didn't seal the surface as you ground or sandblasted as you mentioned). You must seal the surface immediately. Just as soon as you have a shiny section you have to seal it. Moisture in the air instantly starts the rusting process.
Did Seal It
I sprayed primer on immediately behind the guy doing the sandblasting. But you are right, it is probably rusty. I pulled it out of the water in February and I couldn't see anything, but I probably wouldn't until the fiberglass starts to peal.
I sprayed primer on immediately behind the guy doing the sandblasting. But you are right, it is probably rusty. I pulled it out of the water in February and I couldn't see anything, but I probably wouldn't until the fiberglass starts to peal.
clean first of course ... then galvanize
If you are going to sandblast, scrape, acid clean anyway... might as well explore galvanizing...
If you are going to sandblast, scrape, acid clean anyway... might as well explore galvanizing...
Attachments
Phosphoric Acid
I've had excellent results etching & priming marine metals with phosphoric acid based products, such as "Ospho", West Marine "Rust-Lock" etc. The phosphoric acid converts the rust (iron oxide) to iron phosphate (which is inert), and also etches the metal, so that the subsequent coating (if used) get a good bite. I've found that the polyurethane type products, such as Pettit "Rustlok" (#6980) are subject to mechancical damage (scratching, chipping, etc.), and don't work as well under those circumstances. "Ospho" is pretty "thin" (& an acid) so take care when applying it overhead. While "galvanizing" might work, I'd think it too expensive (done properly) to be practical. Regards, Gord
I've had excellent results etching & priming marine metals with phosphoric acid based products, such as "Ospho", West Marine "Rust-Lock" etc. The phosphoric acid converts the rust (iron oxide) to iron phosphate (which is inert), and also etches the metal, so that the subsequent coating (if used) get a good bite. I've found that the polyurethane type products, such as Pettit "Rustlok" (#6980) are subject to mechancical damage (scratching, chipping, etc.), and don't work as well under those circumstances. "Ospho" is pretty "thin" (& an acid) so take care when applying it overhead. While "galvanizing" might work, I'd think it too expensive (done properly) to be practical. Regards, Gord
Phosphoric Acid
I've had excellent results etching & priming marine metals with phosphoric acid based products, such as "Ospho", West Marine "Rust-Lock" etc. The phosphoric acid converts the rust (iron oxide) to iron phosphate (which is inert), and also etches the metal, so that the subsequent coating (if used) get a good bite. I've found that the polyurethane type products, such as Pettit "Rustlok" (#6980) are subject to mechancical damage (scratching, chipping, etc.), and don't work as well under those circumstances. "Ospho" is pretty "thin" (& an acid)so take care when applying it overhead. Regards, Gord
I've had excellent results etching & priming marine metals with phosphoric acid based products, such as "Ospho", West Marine "Rust-Lock" etc. The phosphoric acid converts the rust (iron oxide) to iron phosphate (which is inert), and also etches the metal, so that the subsequent coating (if used) get a good bite. I've found that the polyurethane type products, such as Pettit "Rustlok" (#6980) are subject to mechancical damage (scratching, chipping, etc.), and don't work as well under those circumstances. "Ospho" is pretty "thin" (& an acid)so take care when applying it overhead. Regards, Gord
Underwater Zinc
Issue 83 (June/July 2003) of "Professional Boatbuilder" magazine has an interesting article (Waterline Yachts), wherein a Steel Yacht Builder discusses (among other things) the reasons they DON't use (flame-sprayed) zinc underwater (they do use it top-sides). He claims that the (underwater) zinc layer gets eaten away, after the overcoating paint film gets abraded (or whatever). There's some good information to be gleaned from the article (which I could fax upon request). www.proboat.com Regards, Gord May <Gord@BoatPro.zzn.com>
Issue 83 (June/July 2003) of "Professional Boatbuilder" magazine has an interesting article (Waterline Yachts), wherein a Steel Yacht Builder discusses (among other things) the reasons they DON't use (flame-sprayed) zinc underwater (they do use it top-sides). He claims that the (underwater) zinc layer gets eaten away, after the overcoating paint film gets abraded (or whatever). There's some good information to be gleaned from the article (which I could fax upon request). www.proboat.com Regards, Gord May <Gord@BoatPro.zzn.com>
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