Coppercoat and Iron Keel

[GeoffV]

Had my Cruiser 37 Coppercoated in 2016 by Osmotech before its first launch (not cheap, but was looking for year on year savings to cover it). However this year on haul out the Coppercoat on the iron keel has come away in patches in many places with resultant rusting.

Also, in some places the coppercoat if using a boxknife to get between the coppercoat and the keel to find where its sound, flicks off a square inch or so at a time - it clearly has not bonded with the iron but is squeaky clean with no rust so what is going on?

I will bodge it for this year, but for next year I want to re-coppercoat the keel myself. However, if a good result cannot be guaranteed then I might have to revert to eroding antifoul for the keel which would be a sad result.

[Symphony]

Exactly my experience with my 33 also done by Osmotec. I patched once 3 years ago andd this year bit the bullet and had the keel blasted, then 6 coats of Hempadur epoxy followed by 1 litre of Coppercoat which did about 5 coats of the shallow draft keel plus 10cm strip of the hull around the keel root. The blasting and first coat of epoxy was done by Paul Hokey of Symblast. He supplied the 5l of epoxy, mixing pots and rollers. His bill was £390 and the Coppercoat was £90. It took 12 days, 4 days for blasting and epoxy, 2 day break for weather, 1 day Coppercoat and 5 days cure before launching in the hot June weather. Looked lovely and shiny, but only time will tell if it works.

[GeoffV]

That sounds like a good deal.

Has he found that a better base for the coppercoat than the Interprotect. Its the lack of adhesion that I find the most concerning.

[Symphony]

Paul assured me that the Hempel is superior to Interprotect. It is designed for use on metal tanks etc on commercial ships and seems much denser than the lighter epoxies. Important to put the first coat on immediately after blasting. Expect you will find some rough patches in the casting after blasting. I filled and faired these with Watertite after the first coat of epoxy.

[Symphony]

Before and after shots. The earlier repairs can be seen which were mainly successful, particularly on the bulb and leading and trailing edges, but as soon as I scraped the new rust spots and any bubbles the coating flake off. In all about 25% of the keel needed repair, but after discussing with Ewan at AMC took the decision to blast and start again. The additional cost of using Coppercoat rather than conventional AF is small - the money is in the preparation and the only effective way of getting the iron clean enough is blasting.

I had the boat lifted onto the blocks so that we could get underneath most of the keel base. The rest I coated with AF after scraping .

[GeoffV]

Thanks for the pictures. Very random patterns just like mine. Its a pity there is not an antirust treatment that you can put on before the epoxy as belt and braces!

Another thought I have had - do you know of any any impurities left either on the surface or just below it after the casting that might affect the longevity of the binding epoxy?

[Symphony]

The only way of stopping rust is to exclude air and water, and that is what the epoxy is for. Osmotec grind off the coating applied at the factory before applying epoxy. I watched mine being done and it certainly looked thorough, but not sure it is as good as blasting. I suspect that is the root cause of poor adhesion. Paul had the whole keel coated within 30 minutes of blasting. There were some small areas of pockmarking, mainly on the other side of the keel from the photos where there were obvious imperfections in the casting, but they were as clean as the rest and were coated with epoxy before filling and fairing with Watertite.

Like you my hope was that Coppercoat would pay for itself over the 10 years or so I hope to have the boat, plus avoiding the graft of antifouling each year. I was a bit ambitious in thinking that I could avoid haulouts by just having a lift and clean once a year, partly because the saildrive needs more frequent cleaning. Last year I coated the prop blades with Velox which is excellent, and applied extra coats of Trilux to the saildrive this year so I might try leaving it 2 years. Fortunately haulouts are not expensive at our club.

Pity Bavaria did not offer the option of a lead keel as they used to with some earlier models.

[GeoffV]

Many thanks for your help and information.

[sy_Anniina]

Anyone used Zinga cold galvanization on steel keel before epoxy? As far as I understand, this should prevent corrosion and provide excellent adhesion. The only challenge would be that you'd want perfect epoxy barrier coat before Coppercoat to prevent zinc-copper electrolytic pair

[Symphony]

Keels are cast iron, not steel. Zingard is designed for sheet steel which might otherwise be hot dip galvanised. I have used similar preparations on galvanised steel bilge plates where the galvanising has been damaged. It's advantage is that it is a final coating which leaves a layer of protective zinc on the metal. Galvanised steel has a long life providing it is not subject to abrasion. On my old wooden boat the galvanised fittings (pulpit, pushpit, stemhead fitting) I added in 1988 showed no sign of deterioration when I sold it last year.

Not sure there is any benefit at all applying it to a cast iron keel. As I explained earlier the way to prevent iron rusting is to isolate it from air and water, and that is exactly what the epoxy coating does. The challenge (which also applies to Zingard) is getting it to adhere to the metal substrate. If you read the data sheets for both Zingard and Hempadur (which I used, although it is similar for all epoxies) the keys to good adhesion are cleanliness, surface finish, temperature and humidity. Shot blasting in warm dry conditions then immediate coating achieves this.

[marioxp]

Keels are cast iron, not steel. Zingard is designed for sheet steel which might otherwise be hot dip galvanised.

Dear Symphony, I found on Zinga website "Can I apply ZINGA on any surface? ZINGA has been developed to protect ferrous structures." Cast iron is ferrous.

[Impavidus]

GeoffV
I would be interested to know if you contacted Osmotec? We had an issue with our keel copper coat being applied too thin. It was rectified by Osmotec and we stopped them working when they did not follow the Coppercoat guidelines. The primer they used is now failing and we written to them again. No reply..... Perhaps they will say something when we send them the link to the video we are going to do. So far we have yet to talk to someone that is happy with Osmotec's hull coating procedures and their longevity.... Ant.

[symphony2]

My boat (see above) was done by Osmotec. The hull is absolutely fine but the keel started to get spots after 2 years. I patched it twice then as you can see last year (after 5 years) I had it blasted and recoated it myself, seemingly successfully. I think the basic problem is that they ground off the original factory coating - they did a thorough job as I inspected every day - rather than blasting. Maybe the problem is the epoxy they used after grinding, but i did not see what it was.

Anyway took the view that trying to get them to rectify and then not being confident it would be any better I decided to do it myself using Symblast (Paul) who also recommended Hempadur. He applied the first coat immediately after blasting and I did the rest. Cost was modest as I did it in my normal club haulout and now I have only myself to blame. So far so good. lifted a couple of weeks ago after 9 months in and everything fine so just washed it and back in the water - been out sailing today. As you can see keel is clean and no sign of breakdown, only a chunk of weed on the 2 patches where she sat on blocks. Prop also clean as the blades are coated with velox.

[Impavidus]

Symphony2
Very similar to our issue. Hull is fine keel is pants :-( Thanks for that. Ant.

[Mirror45184]

Grinding or wire brush is generally not the best preparation for painting, sand blast and zinc primer or sealing coat within 3 hours of blasting is teh only way to go.

[Impavidus]

Yes that is why we stopped them last time. It should be blasted to SA 2.5 Two part zinc rich epoxy which is not solvent based. 60 Microns wet film thickness per coat and minimum of 3 coats applied within seven hours. Otherwise it simply will not adhere....
Ant.

[Mirror45184]

Paint adhering to the cast steel is one issue the other is formation of "flash rust" on the keel surface. This will cause rust to continue under the epoxy coting and cause the whole lot to flake off!

[symphony2]

That is avoided by applying the first coat of epoxy immediately after blasting.

[MagicalArmchair]

Iron is porous though - what if water has penetrated the iron? It needs time to breathe and for the water to seep out or be drawn out doesn't it?

[symphony2]

Think that really depends on the specific circumstances. The comment was related to flash rust which can occur very quickly, particularly if humidity is high. This can be avoided by either coating with epoxy immediately or applying a coating which holds back the flash rust until the proper coating can be applied.

In my case the keel had always been coated from new with epoxy, first the factory coating, then the first application of Coppercoat, so doubt there was any moisture in it. The afternoon it was done was hot (20+) and low humidity, perfect conditions. The blasting did expose some imperfections, areas that were rough and slightly pitted, but most of this was filled by the 5 coats of Hempadur.

As to older existing keels that have not been coated with an impervious coating from new, there does seem a reluctance amongst professionals to apply epoxy or Coppercoat without "drying out" first.