Preparing worn keel for Coppercoat - anticorrosive treatment required?

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beormakate

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Sv Marko Island, Montenegro
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We are using Coppercoat for the first time this year. The keel (iron encased in fibreglass) has been sanded back, taking off all old antifoul/epoxy primer and has revealed several places where the keel is exposed - where fibreglass has come off in pieces, holes in the resin where keel weeping, etc. I need to prep our keel before applying the Coppercoat.

We are going to give the underside 3 coats of Awlgrip Hullgard before Coppercoating (once faired and sanded inperfections). The reason for using this is that we are also Awlgripping the hull. Hullgard is a suitable base for Coppercoat.

Is it enough to sand/wire brush? back the exposed bits of the keel then glass over with West System (and mat where required), before fairing (with Awlfair) then Hullgard? Or does the keel need some kind of anti-rust/corrosive treatment (or even a layer of Hullgard before fibreglassing as it is anti-corrosive) before fibreglassing?

Any advice greatly appreciated as there is no point whacking all these pricey items onto the boat if what is underneath is slowly corroding away!

Thanks,
Katie
 
There have been many threads on this subject and it may pay you to search for them.

Cast iron is very difficult to prepare perfectly as it tends to be porous and any wetness can lead to galvanic reaction between the iron and its graphite. It is generally accepted that the order of effectiveness in good preparation goes:
Grit blast
Needlegun
Angle grinder
Sanding (orbital, belt, etc)
Wire brush. This one is particularly poor as it drives debris into the 'pores' of the metal, where it subsequently corrodes.

In your case you are repairing holes in an outer skin, for which I would use an angle grinder. I have successfully repaired damage to my Coppercoated keel this way, followed by West epoxy and many coats of Coppercoat. The epoxy needs to be applied within a short time after grinding, 30 minutes is often quoted.
 
I did the very same job last year. Luckily the yard allowed grit-blasting (with the work area suitably shielded). A needle gun was also used for the worst area. Then epoxy primer rolled on within minutes, followed by epoxy fairing then re-encapsulating the keel area with epoxy and glass*, then final fairing, more epoxy, and Coppercoat rolled onto it 'green'. This is certainly the preferred approach.

* don't use thick rovings on vertical surfaces: gravity sucks harder at them :)
 
The cleaner you can get the metal surface, the better. The thicker the layer of epoxy (to act as barrier between the air/moisture and the metal), the better. And the thicker the layer of Coppercoat, the bettter. When it comes to painting and protecting metal surfaces used in immersion conditions, there's no such thing as over preparing the surface or over protecting it.

On a different topic, and noticing your current location, I've just taken delivery of a bottle of red wine from Montenegro - which will be a first for me (I'm generally a Bordeaux man). Fingers crossed its £7 well gambled!
 
Reality check:
Cast iron is porous so you can expect some moisture to present, this should be removed, heat is faster than drying over weeks or even months.

When dry it should be blasted to class 2.5 ( all over light grey with no shadows) then coated immediately because Cast Iron will flash rust in a mater of minutes with the right conditions, like high humidity or windy.

You only need 3 elements to get rust. Oxygen, moisture and iron.
Remove any one of them and you have no rust.

The alternative to the above is to do repairs whenever you haul out

Good luck and fair winds. :)
 
Just back from shopping in Aldi, where a useful solution might be available at relatively low cost (may not be much use for Montenegro, though). They currently have an air compressor for £99 and a spot grit blaster for £10. I have used the latter previously and it worked well on small areas, pretty impressive.
 
Following doing the best that can be done on the surface preparation as described above, I've had good results using cleaner / phosphate / paint from KBS on my cast iron keel, prior to applying Coppercoat.

If you search for KBS rust seal you should find it.
 
Some of the replies so far seem to assume this is a bolt-on external iron keel that is rusting, as they all do, mine included.

From the OPs description however it sounds as though this is an encapsulated iron keel - ie where the fibreglass IS the hull of the boat and hence very much structural rather than the thin cosmetic layer of filler/resin used on many production boat external iron keels.

If it IS an "encapsulated iron" keel where the GRP has holes, then you are likely to have large areas in the GRP/iron interface that are delaminated and wet: I'd want to check this out and make sure everything was very dry before sealing it all up. This might involve drilling more holes and injecting resin once you were sure it was dry. Before spending much money on Awlgrip/Coppercoat etc. I'd prefer a surveyor to look at this.
 
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On a different topic, and noticing your current location, I've just taken delivery of a bottle of red wine from Montenegro - which will be a first for me (I'm generally a Bordeaux man). Fingers crossed its £7 well gambled![/QUOTE]

Montenegrin reds tend to be full bodied so you'll probably like it. Quality varies, of course, but you can still get a reasonable bottle of Vranac for under 4 euros. We are in Croatia at the mo actually where the whites tend to outshine the reds and not as cheapy cheap as Monte.
 
thanks for the tips. Very useful. Feel like we've bitten off a bit more than we can chew this time - revamping topsides and below waterline in one hit, during a wet and windy and not quite warm enough Croatia, with timescales slipping and deadlines looming.........if I had to do it again, I think I'd take it one job at a time. Too late now, mind you.

When progress is made on keel, Ill try to update thread. We've been advised by shipwright friend to wash wash wash after grinding back to sluice out the salt crystals before patching it up......so then I guess it might go rusty again in drying process.....we have no other tool for the job other than the trusty grinder so that will have to do.
 
beormakate said:
When progress is made on keel, Ill try to update thread. We've been advised by shipwright friend to wash wash wash after grinding back to sluice out the salt crystals before patching it up......so then I guess it might go rusty again in drying process.....we have no other tool for the job other than the trusty grinder so that will have to do.
Click to expand...

That is advice that I totally agree with. A pressure washer could be even better, but in your case you need to ensure that water is not driven between the GRP and the iron.
 
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