Best primer for cast steel keel and grounding plate

[Ian_Edwards]

I'm in the process of getting the cast steel grounding plate and keel professionally blasted and primed ready for CopperCoating.

The work will be done in a temperature and humidity controlled environment, and the first coat of primmer will be applied to the newly blasted steel as soon as practically possible.

However, I have to make a decision on which primer to use and I'm currently looking at International and 3m products and getting advice from their technical sales people.

Does anyone out there have any first hand experience of priming cast steel, which is about 10years old?

I'm particularly interested in getting feedback on how long the primer lasted, it's an expensive exercise and I really don't want to have to repeat it!

 

[Tranona]

Use the primer recommended by Coppercoat. It is a 3M product. I used it on my keel Goes on easily and possible to get 2 coats in a day if conditions are right. I did mine in mid summer in the open so managed the whole process including the Coppercoat in 5 days. Better (or more controllable) indoors of course.

If it adheres properly then the primer lasts the life of the Coppercoat (at least).

 

[Ian_Edwards]

Thanks for the reply, That's what is currently on the boat, but it's flaking off, it's lasted 5 seasons.

QUOTE: If it adheres properly then the primer lasts the life of the Coppercoat (at least). End Quote

It was applied professionally, but I can't say whether is was applied properly or not, it was applied in doors in a controlled environment.

I'm just casting around for other options to consider before giving the go ahead for the work.

 

[duncan99210]

I talked to them recently and, IIRC, they recommended using International Primocon. Applied asap after cleaning the metal and five or six coats of it. Amongst the reasons for recommending this primer is the fact that it dries to a rough finish somthe coppercoat can go straight onto it with no further preparation. I'm tempted to follow this route but may apply a few coats of expoy paint before the CC.

 

[Tranona]

Thanks for the reply, That's what is currently on the boat, but it's flaking off, it's lasted 5 seasons.

QUOTE: If it adheres properly then the primer lasts the life of the Coppercoat (at least). End Quote

It was applied professionally, but I can't say whether is was applied properly or not, it was applied in doors in a controlled environment.

I'm just casting around for other options to consider before giving the go ahead for the work.

The job I described was done because some of the original came off the lower bulb area of the keel after 2 years. Also professionally applied in the summer under cover. However it is still firmly attached to the other 90% of the keel so not convinced it is the coating itself that is the problem. As the conditions were good for working outside and the cost of completely cleaning and starting again would have run into 4 figures I decided to do it myself. I ground off the affected areas and used the 3M epoxy and then Coppercoat. As ever, only time will tell as to whether my decision was wise. Lifting again in March so that will be first chance to inspect.

I have talked to several people who have experience (good and bad) of this issue with iron keels and there seems to be no pattern to be definitive as to why some (very small number?) fail.

Should add that the original application was on a new boat and done less than 2 weeks from leaving the factory. However the original coating on the keel had to be ground off as it was incompatible with Coppercoat.

 

[MM5AHO]

When you say "grounding plate" what do you mean? A grounding plate for an SSB radio? If so then won't painting that mean it's not electrically connected to the sea? (but capacitively connected through the paint as a capacitor dielectric)

 

[VicS]

When you say "grounding plate" what do you mean? A grounding plate for an SSB radio? If so then won't painting that mean it's not electrically connected to the sea? (but capacitively connected through the paint as a capacitor dielectric)

According to the OP's profile he has a Southerly!

 

[Dazedkipper]

3M Scotchkote GP120.
2 pack epoxy primer.

 

[Ian_Edwards]

When you say "grounding plate" what do you mean? A grounding plate for an SSB radio? If so then won't painting that mean it's not electrically connected to the sea? (but capacitively connected through the paint as a capacitor dielectric)

No, the grounding plate is 4 tones of cast steel recessed into the the bottom of the boat, it's designed for the boat to dry out on, and to provide the ballast to keep the boat upright when the 2.5 ton swing keel is up. The Southerly just makes category A when the keel is up.

 

[flyingscampi]

Westerly Storm with cast iron keel.

In 2009, Coppercoat recommended Hycote 152 which I ordered in two different colours to make it easy to apply coats. The keel was blasted before application.

The rust started popping through in 2015 and last year I had to treat the affected areas by sanding back to bare metal and using Fertan (which was good for last season at least.)

 

[Quandary]

Jotun Jotamastic 87 is a high solids two pack epoxy designed for steel structures (oil rigs) there is a winter grade available that can be used down to 10 degrees C, it can be used successfully over rusted surfaces if necessary, not expensive for a 2 pack epoxy. I would recommend Jotuns Vinyguard 88 if you must use a single pack paint or, if going for a super finish, the 88 over the Jotamastic.
Vinyguard 88 is similar to Primocon but having used both I prefer Jotuns stuff. My impression is that Jotamastic 87 winter grade cures relatively soft but I used it at low temperature and perhaps slightly overthinned it, but Jotun make other versions (for instance Jotamastic 90 is coloured) all targeted at marine use.
I have it on my cradle which sits a few yards from the sea and is dragged around the yard, I have also primed the iron keel and the saildrive leg with it.
SML coatings have the whole range of Jotun paints and their carriage charges are reasonable and they know the product specs well; Jotuns website is very comprehensive when making a selection.

Having said all that, is there a reason not to follow Coppercoat's specification?

 

[Ian_Edwards]

I've tried various primers:

I'm not sure what Southerly used when the boat was new, but it wasn't CopperCoated at the stage.

When I bought the boat I has it CopperCoated by HYS, they used Hycote 152, which I think was recommended by CopperCoat.

Silvers did some work on the boat in 2014/15, and I don't know what hey used,

I did some work on the boat is 16/17 and used 3M Scotchkote GP120, 2 pack epoxy primer., which is what CopperCoat recommended at the time.

None of the primers have lasted more than a couple of years, so I was trying to tap into the vast experience available on this forum to see what others have used successfully, as part of the research being done before we bight the bullet and re-coat the keel.

Thanks for the input we'll put Jotun's on the list to talk to.

I've also investigated Coal Tar epoxy, a 2 pack which is used extensively in the North Sea oil and gas industry and seems to be very durable.

 

[Pasarell]

Many of the answers so far are based on coating cast iron which is very different to steel. Assuming your grounding plate is actually steel then you have a much simpler task than when coating cast iron.
You say the job is being done in a controlled atmosphere so, again, you have quite a simple task.
The problem before, and with many of the other respondents will be salt in the metal and not with the primer used. The ideal way to deal with your grounding plate is to blast it to remove old coatings and all corrosion. The blast standard is normally known as Sa2.5 but don't necessarily expect a yacht blaster to know what that is. When the metal has been blasted and all traces of old coatings and corrosion have been removed pressure wash the steel with fresh water and allow to dry. On something as small as this you can force dry with warm air to speed the process. Blasting will have forced very small salt crystals into the steel and these will be the cause of future corrosion. Pressure washing removes the salt crystals.
When the steel is dry blast again. This second blast needs to be with a dry aggregate even if the first used slurry.
After the blast clean dust away with clean, dry, compressed air and then coat with your chosen primer. Taking time to dry the steel before 2nd blast and remove dust and debris is far more important than rushing to get the primer on. You have at least a couple of hours before you need to start coating, probably more in a controlled atmosphere.
As for product to use, there are many that are suitable. I would go for one from a major marine coatings supplier (International, Hempel, Jotun etc) rather than a smaller supplier just because that is their business and they have a huge turnover so materials are always "fresh". Along with any other smaller companies they all supply products "used on oil rigs" etc. Coat tar epoxy was very good until it was banned about 20 years ago. Now synthetic tar materials try to trade off the name and, anyway, they were for coating areas with imperfect preparation.
In your case it sounds as though an abrasion resistant epoxy such as glass flake would be the best but it will be more difficult to overcoat with whatever goes on next.
Whatever product you choose make sure you put on enough. A dry film thickness gauge would be a good investment and they are cheap on ebay now. The 2 main causes of coating failure are poor surface preparation and inadequate coating thickness.
Just bear in mind when talking to the technical departments of any coating company that if it is their yacht departments their main experience is with GRP. Best advice will come from protective coatings advisers but they will probably recommend product names that you cannot get in small packs or from a retailer.

 

[Ian_Edwards]

Thanks Pasarell, lots of useful information in your reply.

I was aware that the original coal tar epoxy was banned, I seem to remember it was carcinogenic. I know that when I was involved in removing Brent Spar, the steel, which had been coated with coal tar epoxy was, a good as new. It also seems likely that, however hard we try, the preparation will be imperfect to some degree, which is one reason why I thought of Coal Tar Epoxy.

After reviewing my notes of conversations with CopperCoat, it seems like they think two things are really important, in addition to the common sense stuff you normally do when applying a coating. The first is that the primer should be solvent free, you can use a primer which contains solvents, but you have to wait a long time before overcoating with CopperCoat, to allow the solvent to evaporate. The second is that CopperCoat should be applied to a well abraded surface, unless it is applied to a water based primer before it is completely cured. They are obviously concerned about it adhering to the primer.

I'm still researching the "best way" to apply a primer, and still haven't come to a conclusion, I'd really like to get right this time.

The keel and grounding plate are described as cast steel, from Iron Brothers.

The photo was taken after Silvers had blasted and primed it in 2015.

 

[Pasarell]

Ian, the advice about overcoating primers are a bit silly. Of course you need to allow solvents to escape from a solvent based primer to avoid entrapment and blistering. However, you should also allow a solvent free material to cure fully before overcoating as you don't know if it will be compatible with the subsequent material. Times are about the same, at least 7 and up to 28 days if you want to be totally confident. Since you are able to control the temperature you should be able to work at the shorter end of the scale. The well abraded part is because they need a mechanical key to the primer rather than a chemical key if you apply "wet on wet". Just to be clear a water based primer is solvent based - the solvent is water! There is no guarantee that 2 different products will be compatible just because they are water based.

 

[duncan99210]

I talked to them recently and, IIRC, they recommended using International Primocon. Applied asap after cleaning the metal and five or six coats of it. Amongst the reasons for recommending this primer is the fact that it dries to a rough finish somthe coppercoat can go straight onto it with no further preparation. I'm tempted to follow this route but may apply a few coats of expoy paint before the CC.

I've now got round to checking my notes on the phone conversation.... Its not Primocon they recommend but Interprotect, a two part epoxy primer. Makes much more sense.

 

[oldsaltoz]

I'm in the process of getting the cast steel grounding plate and keel professionally blasted and primed ready for CopperCoating.

The work will be done in a temperature and humidity controlled environment, and the first coat of primmer will be applied to the newly blasted steel as soon as practically possible.

However, I have to make a decision on which primer to use and I'm currently looking at International and 3m products and getting advice from their technical sales people.

Does anyone out there have any first hand experience of priming cast steel, which is about 10years old?

I'm particularly interested in getting feedback on how long the primer lasted, it's an expensive exercise and I really don't want to have to repeat it!

 

[EwanClark]

As the manufacturer of Coppercoat, I would just like to add a bit of information to this thread.

Firstly, under no circumstances use International Primocon, or indeed any single pack primer, before applying Coppercoat. All epoxies, not just Coppercoat, must be applied to a sound and permanent substrate, normally gelcoat or previously applied epoxy coatings.

For many years we have used a range of epoxies from 3M with great success. Unfortunately 3M have recently ceased production of these products. There are many equally suitable products available on the market and in this case we would recommend using International Interprotect. We would advise applying several coats of Interprotect, following their application instructions. It is important when treating pitted cast iron that a complete "skin" of epoxy is applied, so it pays dividends to be very thorough with the application. We find application by roller is best but also use a brush to "stipple" the Interprotect into any pin holes or voids that become visible after any coat. Interprotect, being a heavily solvented epoxy, should be allowed to cure for at least 5 days before applying Coppercoat, to prevent solvent entrapment.

If anyone has any questions about appropriate primers, or indeed any questions about Coppercoat, please feel free to contact us on +44 (0)1258 861059 or via the details below.

 

[Ian_Edwards]

Re: Update - Best primer for cast steel keel and grounding plate

Just a quick note as an update on progress.

Both the keel and grounding plate have been blasted to SA2.5 and have been coated with 5 coats of International Intershield 300, as advised by CopperCoat.

It's now resting to ensure all the solvent has evaporated before the CopperCoat is applied.