MoodySabre
Well-known member
That's what I do - the amount needing treatment each year is getting less so it is effective.
Rusty Keel
- Thread starter Sailfree
- Start date
That's what I do - the amount needing treatment each year is getting less so it is effective.
rogerthebodger
Well-known member
If you wish to prepare any metal for painting the best is to dry grit blast to the spec indicated above.
Grit blasting does 2 things that make the epoxy to stick better.
1) It cleans the service of rust, mill scale and any oils on the service.
2) It roughens the surface to give the epoxy a much greater service area to adhere to.
The painting must be done within a short time otherwise the surface will start to rust the time limit is dependant on the weather conditions.
Grit (slag) is better than sand as it has sharper edges to give a rougher surface and is generally harder also giving a rougher surface.
Dry blasting is better than wet as water on a newly cleaned steel of cast iron surface will rust very quickly and to paint the surface must be dry.
To dry blast you need a high power compressor, normally engine driven of the kind used in road construction.
I have one of the heavy duty version of the type you show and have never used it successfully during my boat construction.
There is also a "small" dry blasting pot available which is better for small jobs but you still need a large compressor.
The painting of the first coat of paint shown took twice the amount of paint as following coats due to the roughness of the surface created by the grit blasting
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vyv_cox
Well-known member
The OP asked the question in March. He almost certainly patched it up and has been sailing for a couple of months by now.
Whilst I agree that grit blasting is the ideal treatment, the question referred to rust patches. In most cases removing the rust with an angle grinder, painting with a primer and antifouling is all that most people want to do. Hammerite would not be my first choice and I find that Primocon needs very good treatment of the surface to ensure that rust does not return beneath it.
Whilst I agree that grit blasting is the ideal treatment, the question referred to rust patches. In most cases removing the rust with an angle grinder, painting with a primer and antifouling is all that most people want to do. Hammerite would not be my first choice and I find that Primocon needs very good treatment of the surface to ensure that rust does not return beneath it.
ghostlymoron
Well-known member
Due to a slight accident, I had my keels treated professionally as part of the insurance work. They were lightly blasted, immediately primed with Hempadur then anti fouled. The result were spectacular compared with the amateur treatment they had had over the preceding years and will probably not need treating again for 5 years. Without sandblasting you can't expect to produce a durable result. It was expensive though.
jakeroyd
Active member
I tried this last year.
I had pits in my keels about say 4mm deep.
Like many I ground out and wire brushed , treated with Vactan.
But then I used Epoxy putty to fill and fair the holes back to the surface.
I then coated with Epoxy Tar and Antifouled.
On coming out this year they were still as they when tin the water last year (apart from the AF!)
Just wanted to add the bit about Epoxy putty if you have deep bits.
I had pits in my keels about say 4mm deep.
Like many I ground out and wire brushed , treated with Vactan.
But then I used Epoxy putty to fill and fair the holes back to the surface.
I then coated with Epoxy Tar and Antifouled.
On coming out this year they were still as they when tin the water last year (apart from the AF!)
Just wanted to add the bit about Epoxy putty if you have deep bits.
rogerthebodger
Well-known member
For rust spots I would recommend using a welding chipping hammer or better needle de scaler if compressed air is available then use and angle grinder with a cup wire brush and not a grinding or sanding disc.
Use what ever rust converter followed with epoxy tar IMHO the only thing good enough for steel below the water followed with your choice of anti fouling.
kunyang
Member
I used an American product POR 15 in the winter, I should soon learn how good the treatment is! It is a three process treatment, and was recommended to me.
vyv_cox
Well-known member
Wire brushing is not recommended for iron keels, rust is driven into the surface where it will lead to bonding issues in a fairly short time. Needle gunning is an excellent treatment, used on offshore oil platforms where blasting is not possible. Unfortunately it is rarely an available option to most people. Grinding is the next best option, far better than wire brushing.
Pasarell
Well-known member
Vyv is, as usual, right with his comment above.
There are many ways to treat corrosion of ferrous metals. All have their merits and many have disadvantages. Always the purpose is to remove as much of the corrosion product as possible then exclude at least one of the things necessary for it to progress in future. Corrosion, as far as cast iron or steel keels are concerned, needs a ferrous metal, oxygen and moisture to occur. If you get the metal clean then remove at least oxygen or water, preferably both, you won't get any corrosion. Simple.
Most boats have cast iron or occasionally steel keels. Getting cast iron clean is almost impossible so all you can do is reduce it as much as possible. With corrosion products left on the surface it will rust in future whatever you do. Despite that, removing moisture and oxygen from the surface will delay future corrosion.
The best way to clean any ferrous metal is dry abrasive blasting (not with sand). Next best is to use a needle gun. Third is grinding and a distant fourth is wire brush.
Blasting and needle guns are quite good at removing corrosion products. Grinding has some effect. Wire brushing has little effect - but it does a great job of polishing the rust to a nice shiny finish and making it look nice.
Ultra high pressure water (>35K psi) is also very effective in combination with modern primers and would be particularly suitable on porous cast iron as it has the added benefit of removing salts but is rarely available or cost effective for boats.
None of the dry systems (blasting, needling, grinding) will do anything to remove salt or grease (contrary to one of the comments above) so for an effective job have to be combined with other, usually wet, cleaning methods.
Cast iron is a particular problem as it is usually full of pit holes and pores that retain salt, water and other contaminants so the only chance of being effective is repeated wet and dry treatments. Unlikely to be practical in the real world and this is usually the reason for quick breakdown of a repair.
Once a keel is prepared by one of the 3 best systems it is important to get a primer on as quickly as possible BUT it is often better to give the surface a good pressure wash first even though there will be some surface flash rusting as a result than to put the primer on without washing. If the metal is clean the flash rust will have a light ginger colour. It the surface is not clean the flash rust will be black. Most good primers today are surface tolerant enough to go over flash rusting provided any powdery rust has been removed. The surface does have to be dry though.
If the surface is prepared by blasting, needling or grinding then rust converters have no benefit and will probably be harmful. There is a very good reason why none of the marine paint companies produce or recommend them! They do have a place if preparation is by wire brush but will only make a marginal improvement.
Primers have the role of keeping water and oxygen from the surface. To do that they have to be thick enough and this is often the cause of failure. Look closely at the surface of the metal after preparation and it will have many indentations - and many spikes. Rolling the first coat of primer on will often bridge the indentations, leaving air pockets underneath, and not cover the spikes. Brushing and working the paint in will be better in the indentations but still leave the spikes exposed. Primocon, probably the most used keel primer in the UK, is less than 50% solids and will be applied by brush at 30 - 50 microns wet film. This means that each coat, when dry, is about 15 - 20 microns thick. To put it another way, it will take at least 5 coats to put on a dry film as thick as a sheet of paper. And that will only be over the smoother metal. Over the spikes there will be virtually nothing and the reason why your keel will have rust patches again next year.
Someone said earlier it is best to apply a primer that contains zinc such as Primocon. It does not contain zinc! Nor do most of the primers now available at retail level. They are simple barrier coats. Zinc is an excellent anticorrosive but I can only assume is too expensive for us yachtsmen.
All the major industrial paint companies (International, Hempel, Jotun etc) supply ships and oil rigs in vast quantities. All their products are very good but increasingly complex. They all used to provide the same products to us in retail pack sizes but increasingly they are different, and seem to be downgraded.
There are no magic bullets when it comes to yacht keels. I get very frustrated by so many of the comments about the "right" way or "all the oil rigs use" comments that are so very misguided. The only way to do it properly is by good surface treatment followed by sufficient quantity of a good primer. It all takes hard work and time.
There are many ways to treat corrosion of ferrous metals. All have their merits and many have disadvantages. Always the purpose is to remove as much of the corrosion product as possible then exclude at least one of the things necessary for it to progress in future. Corrosion, as far as cast iron or steel keels are concerned, needs a ferrous metal, oxygen and moisture to occur. If you get the metal clean then remove at least oxygen or water, preferably both, you won't get any corrosion. Simple.
Most boats have cast iron or occasionally steel keels. Getting cast iron clean is almost impossible so all you can do is reduce it as much as possible. With corrosion products left on the surface it will rust in future whatever you do. Despite that, removing moisture and oxygen from the surface will delay future corrosion.
The best way to clean any ferrous metal is dry abrasive blasting (not with sand). Next best is to use a needle gun. Third is grinding and a distant fourth is wire brush.
Blasting and needle guns are quite good at removing corrosion products. Grinding has some effect. Wire brushing has little effect - but it does a great job of polishing the rust to a nice shiny finish and making it look nice.
Ultra high pressure water (>35K psi) is also very effective in combination with modern primers and would be particularly suitable on porous cast iron as it has the added benefit of removing salts but is rarely available or cost effective for boats.
None of the dry systems (blasting, needling, grinding) will do anything to remove salt or grease (contrary to one of the comments above) so for an effective job have to be combined with other, usually wet, cleaning methods.
Cast iron is a particular problem as it is usually full of pit holes and pores that retain salt, water and other contaminants so the only chance of being effective is repeated wet and dry treatments. Unlikely to be practical in the real world and this is usually the reason for quick breakdown of a repair.
Once a keel is prepared by one of the 3 best systems it is important to get a primer on as quickly as possible BUT it is often better to give the surface a good pressure wash first even though there will be some surface flash rusting as a result than to put the primer on without washing. If the metal is clean the flash rust will have a light ginger colour. It the surface is not clean the flash rust will be black. Most good primers today are surface tolerant enough to go over flash rusting provided any powdery rust has been removed. The surface does have to be dry though.
If the surface is prepared by blasting, needling or grinding then rust converters have no benefit and will probably be harmful. There is a very good reason why none of the marine paint companies produce or recommend them! They do have a place if preparation is by wire brush but will only make a marginal improvement.
Primers have the role of keeping water and oxygen from the surface. To do that they have to be thick enough and this is often the cause of failure. Look closely at the surface of the metal after preparation and it will have many indentations - and many spikes. Rolling the first coat of primer on will often bridge the indentations, leaving air pockets underneath, and not cover the spikes. Brushing and working the paint in will be better in the indentations but still leave the spikes exposed. Primocon, probably the most used keel primer in the UK, is less than 50% solids and will be applied by brush at 30 - 50 microns wet film. This means that each coat, when dry, is about 15 - 20 microns thick. To put it another way, it will take at least 5 coats to put on a dry film as thick as a sheet of paper. And that will only be over the smoother metal. Over the spikes there will be virtually nothing and the reason why your keel will have rust patches again next year.
Someone said earlier it is best to apply a primer that contains zinc such as Primocon. It does not contain zinc! Nor do most of the primers now available at retail level. They are simple barrier coats. Zinc is an excellent anticorrosive but I can only assume is too expensive for us yachtsmen.
All the major industrial paint companies (International, Hempel, Jotun etc) supply ships and oil rigs in vast quantities. All their products are very good but increasingly complex. They all used to provide the same products to us in retail pack sizes but increasingly they are different, and seem to be downgraded.
There are no magic bullets when it comes to yacht keels. I get very frustrated by so many of the comments about the "right" way or "all the oil rigs use" comments that are so very misguided. The only way to do it properly is by good surface treatment followed by sufficient quantity of a good primer. It all takes hard work and time.
Nicholas123
N/A
I slapped on a coat or two of bitumized rubber (the type of stuff they use for house damp course's) mixed with about 10/20% PVA screed stuff (both water soluble) about 15 years ago after wire brushing & washing down most of the rust on my old boat & that seemed ok to me for quite a while.A damn site cheaper & less hassle than most of the preparations I have heard about here & shall probably be doing the same thing again in the future on my new boat.
PS:I think I then applied a coat of Woolworth's acrylic undercoat to enable anti-foul to stick to the surface
PS:I think I then applied a coat of Woolworth's acrylic undercoat to enable anti-foul to stick to the surface
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