Rusty keel

[marioxp]

I struggle with a rusty keel on my B36 2003y. Last year we grind it to bare metal, paint it with Hemperite metal primer paint and after that applied selfpoishing antifouling. It lasted few months after which it peeled off.

This year I want solution which will last at least few years.

Plan is to grind keel to bare metal, holes additionally sandblast, immediately apply Zinga paint (cold galvanzation), after that a layer of Zingalufer (company advice apply it before unknown paint), and this is where my doubts and my questions begin! What next?

One option is to apply 2-4 layers of Light Primer, Hempel's two component epoxy primer for underwaterline surface. But I heard that some people didn't have success with it on rusty keel. Maybe reason is rusting underneath epoxy layer. But no one applied Zinga paint layer underneath epoxy layer.

Other option is to apply 2-4 layers of Primocon, International one component primer for underwaterline surface. Primocon is declarated as anticorosive but is one component and it is not epoxy, also I read that people complained that it peeled off.

Final layers will be Jouton antifouling. 

[symphony2]

The only sure way to deal with it is to have the keel blasted then immediately apply epoxy, followed by a further 4 or 5 coats over 2-3 days. Having gone to all that trouble spend a little extra and coat with Coppercoat rather than standard antifoul. I did my keel like this last year. It cost around £600 for the blasting, first coat of epoxy, 5l of Hempadur and 2 packs of Coppercoat. Lifted last week after 9 months and still perfect.

Before and after photos attached

[Keweetoo]

Last year I took the keel back to bright metal and immediately applied Hemple two pack epoxy light primer on advice of local boat yard who do this regularly. Then fairing with epoxy two pack as necessary, followed by four more coats of two pack epoxy light primer. Just as the final coat is still 'tacky' a coat of underwater  primer and then two coats of your antifouling. This was last year and boat has just been lifted and keel looking like the day it went in after a clean. However I'm sure there are other methods and time will tell if this system will be a good one!

[marioxp]

I took the keel back to bright metal

Did you grind or sandblasting?
I ask because somebody told me that grind is not enough good, but as I understand bare metal is bare metal.

Then fairing with epoxy two pack as necessary

Is this step is also Hempel light primer?

Last year I took the keel back to bright metal and immediately applied Hemple two pack epoxy light primer on advice of local boat yard who do this regularly. Then fairing with epoxy two pack as necessary, followed by four more coats of two pack epoxy light primer. Just as the final coat is still 'tacky' a coat of underwater  primer and then two coats of your antifouling. This was last year and boat has just been lifted and keel looking like the day it went in after a clean. However I'm sure there are other methods and time will tell if this system will be a good one!

How many coats of light primer did you apply in total? How much light primer did you spend per one coat?

[symphony2]

The problem with cast iron used for keels is that it often has porous patches which are difficult to get clean with a grinder. The grinder also tends to polish the surface which can hinder adhesion. some say a needle gun is better in this respect, but I have found in the past they are not easy to use. That is the reason why I had to redo my keel. The boat came from the factory with an epoxy coating that was not compatible with Coppercoat so my contractor ground it off before using a different epoxy. As you can see from the before photo I had already repaired parts (the boat is 5 years old) and other areas were poorly adhered. Hence the decision to start again.

Another problem with grinding is that flash rust can start so you should really put on the first epoxy coating immediately. To avoid this some recommend washing the bare keel with phosphoric acid which cleans the pores before applying epoxy.

Good blasting avoids all this and prepares the surface to the correct finish for maximum adhesion of the epoxy. The whole process from starting blasting to the first coat rolled on took about 45 minutes.

[Keweetoo]

Hi MarioXP
In response to your questions I used a Tercoo Rotary Blaster (https://tercoo.com/en/)  which fits on a drill and did a good job of getting the old fouling off the keel. It does not get into crevices and I used a flap wheel on a grinder and rotary wire brush attachment for drill together with a small 'Dremmel' type wire brush for small crevices. Rotary wire brushed again just prior to applying the first coat of primer. You will need full cartridge type breathing mask/eye protection/disposable overalls and it took two days to complete as you have to be careful with the blaster not to scour the metal. I only did this because I had booked a professional blaster who could not complete the job due to Covid & yard restrictions last May /June and I did not want to wait further weeks before getting back into the water. On balance I would certainly pay the money (I was quoted £300) and get the job done professionally sand blasted.

Faired (filling in the dents and crevices) with Hempel two pack epoxy filler Profair

The first and second coats of light primer took about 75% a 1L tin each and the final coats 1/2 tin each  - I ended up buying 4 X 1L tins and would have been much cheaper to buy the 5L pack and have some spare. Apply by mini roller and if you don't think you will use the whole tin per application then mix in a separate tub (I used old ice cream tubs). The Hempel tins are designed to tip the curing agent into the epoxy paint tin and mix but this means any spare will cure before you can use it!
Good luck

[IslandAlchemy]

Honestly, just stick some antifouling on it and go sailing.

Or buy a lead keel.

[elias]

And I would suggest good quality anodes .

[symphony2]

Anodes are absolutely no help at all. An iron keel rusts in seawater (or any other water for that matter0 - this is not galvanic action.

[JEN-et-ROSS]

Honestly, just stick some antifouling on it and go sailing.

        Yep...That about sums it up..

[elias]

Anodes are absolutely no help at all. An iron keel rusts in seawater (or any other water for that matter0 - this is not galvanic action.

I had the impression that when 2 different metals are bonded the weaker always will be sacrificed. I have to study my chemistry school books again ... sorry for the misinformation

[JEN-et-ROSS]

Hi elias...
  All your cast iron keel needs to rust is the oxygen dissolved in the seawater, and there's plenty of it in seawater. As mentioned above the porous areas will rust more due to increased surface area, but it would take a very log time for your keel to rust away due to its size
The salt in seawater is really only significant when you do have dissimilar metals, as the salt in the water creates an effective electrolyte allowing a healthy current to flow causing the more reactive metal to rapidly rot away. Ensuring the reactive metal is electrically isolated and regular anode replacement should reduce galvanic corrosion almost to zero.(e.g. a saildrive or propeller ) ..................Bill.

[elias]

On my boat, on the huge bolts that keep the keel fixed in the hull , there is a copper cable running from the battery or maybe the panel I can’t remember  . Is that for the anode or something else like thunder  ?

[Yngmar]

There's a copper rod connecting the mast via the compression post to a keel bolt. This is for lightning strikes, to ground them via the keel. You will only lose some paint off the keel (and your masthead fittings and most of your electronics of course) rather than get a big hole in the boat.

[MagicalArmchair]

I cocked this job right up this year. When I lifted, the keel was a mass of rust.



So I ground the keel back to bare metal using flappy discs and then immediately rust treated it...



... the surface the next day had bubbled up nicely, with lots of watery, rusty little holes springing up!!



I chose to grind it back again, pressure washing it and then letting it "breath",  washing with phosphoric acid every couple of days to keep the rust at bay, before applying four coats of epoxy to it, and then antifouling it...

Within days water trapped still inside the porous keel bubbled to the surface and I ended up with the below.



The recommendations to just go sailing would have ended with a far superior result. Oh well! Next year I will try letting the keel stand for a few months to let the water seep out, then get it professionally shot blasted, then try the epoxy route again....

....or I'll prime the rusty patches and go sailing... hmm

A chap on the boat next door who had his Coppercoated at Foxes professionally said they stood the boat for two months at the back of their heated shed and tested his iron keel with a moisture meter before they finally applied the epoxy. His looked stunning some years on without a spot of rust...

[symphony2]

It is a really tricky to know what is the best approach. as i described earlier my keel was ground back by Osmotec literally within a week of it leaving the factory, but it still failed as the phot above shows. It was actually worse than the photo as as soon as I started scraping to do more patching, the coating came off in sheets - hence the decision to blast and start again.

Touch wood (or iron) it seems to have worked as the photo taken last week after 9 months in the water shows. The forest at the bottom of the keel is where the blocks were and although I slathered antifoul on the patches it really did not work. Also shown is the Velox on the prop - now 2 years old and just a light slime on the outside faces of the blades and nothing on the inside.