rust on iron ballast is something you can get rid of.
But stopping it from coming back is another matter, the best you can do
prevent it returning too soon.
Why is Keel Rust a
Well for a start nothing
looks worse than a keel streaked with rust and full of pockmarks.
Especially if you decide to
sell the boat.
But apart from the appearance,
if rusting is allowed to
continue unabated the rust flakes will keep expanding, falling away and
exposing more of the iron which, will in turn rust and fall off and so
ad-infinitum while there is still iron to oxidize.
And because rust expands any
that is allowed to form
behind the paintwork will cause the paint to flake off.
that iron keel won’t disappear overnight, and there is much that you
do to slow the process.
And there is a lot to be said
in favor of the cast iron
It is one of the cheapest and
safest materials to cast a
keel from, it has none of the toxic problems that are associated with
smelting and while way cheaper than many of the more exotic materials
does a perfectly adequate job.
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This is not the easiest or cleanest job in
the world but it is worth the
effort just to keep your pride and joy in good condition.
And at least you won’t be doing it on a daily basis like those
Merchant seamen or yore, constantly chipping rust and repainting their
However, before you start chipping that keel rust, decide on
how you are
going to treat the clean metal and have the paint or whatever ready.
That clean metal will very
quickly begin to
develop a new layer of
rust, so coat it as soon as possible.
There are several ways to clean off the old keel
Just remember that for the protective coating to be successful
you need to
get down to clean metal before it is applied.
Chipping hammer or cold
chisel; Begin chipping off all
the scale, then use a wire brush and sand with coarse paper until
to clean, bright iron. Then use a fine sandpaper to finish.
Angle grinder and discs; Best
to chip off the worst of the flakes first to prevent too many bits
Sandblasting the rusty keel;
While this may be a very efficient method it is very messy and does
specialized equipment. And
you may find that your
boat yard doesn’t allow sandblasting, because of the
Shot blasting is carries the
same problems as sandblasting.
Needle gun; These guns can
usually be rented from a tool rental shop. They work by driving a set
of steel needles into the surface of the rusty
keel. Driven by either compressed air or electric drive, they can do a
good job of getting into the pits and roughing up the surface ready for
While clearly the best way to treat keel rust is to clean the entire
Sometimes though, it is neither possible nor desirable, because of the
problems involved, patching up may be the only option.
And often the keel wont have rusted evenly there will be sound areas
surrounded by pits.
If you are going to patch make sure you get all that rust out of the
before over coating.
And don’t forget the bottom of that rusty keel and
to replace the bungs covering the keel bolts.
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As soon as you get down clean metal
get some form of protective
coating on to it or it will soon start to rust again.
Even if you haven’t
finished cleaning it off
put something on the bits that are clean, just leaving it overnight can
long enough to give you a new layer to clean off.
You could use one of the
numerous a 'rust converter'
compounds that are available.
These coatings contain
metal salts and phosphoric
acid so handle them with care.
work by converting
the ferric oxide (rust) into
ferric phosphate, which produces a gray surface coating which is also a
base coat for subsequent coatings.
still, avoid any
nasty chemicals, and just get
rid of the rust completely.
Then as quickly as
possible slap on a coating of Zinc
Chromate paint or metallic gray primer.
Whether or not you use the
rust converter, apply at
least three coats of the zinc chromate or primer paint to give an as
impenetrable a water barrier as possible.
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If you are
contemplating competing in some prestigious races you might want to
consider faring and smoothing your newly cleaned keel.
But for the rest of us
leisure sailors some pitting
on that once rusty keel isn’t going to make much difference to her
performance but she will go better than she did with all that keel
If the pitting is very bad
you may want to spend some
time fairing it.
There are plenty of epoxy
mastics on the market which
make all sorts of promises but remember that epoxies just won't stick
And when rust gets under
it, which it will
eventually, it is just going to fall off.
And as for encapsulating
the keel in epoxy and
fiberglass, forget it, not only will it be an expensive process but in
opinion, a recipe for future disaster.
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all you need to do is
apply a few coats of the metallic gray primer.
Rubbing down between coats
to get a reasonably smooth
finish then apply your anti-fouling.
And that’s it, job done,
no more keel rust,
well not until next time.
The key is to take your
time with the preparation,
and you will have a job that won’t last forever, but long
Of course, every time you
haul out check her bottom
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