Protecting cast iron
 

I'm doing a bottom job on my boat that has a cast iron keel with a
centerboard slot. Most of the keel stayed rust free but the slot and the
bottom of the keel that often comes in contact with the bottom at low tide
are rusty. I'm going to chip and sand blast but I'm unsure of how to treat
the bare metal before applying the new bottom paint. Suggestions?
Quinton

On Tue, 22 Feb 2005 12:17:36 -0600, "Sail-n-Dive"
wrote:

I'm doing a bottom job on my boat that has a cast iron keel with a
centerboard slot. Most of the keel stayed rust free but the slot and the
bottom of the keel that often comes in contact with the bottom at low tide
are rusty. I'm going to chip and sand blast but I'm unsure of how to treat
the bare metal before applying the new bottom paint. Suggestions?
Quinton

Suggestion #1 - don't allow an iron keel to come in contact with the
bottom

Suggestion #2 - Several layers of epoxy covered by a hard bottom paint


Weebles Wobble
(but they don't fall down)

Good advice, I suspect.

I gather your keel is gray cast iron, probably subject to
corrosion from stagnant seawater under the keel and in the
C/B well.

The keel has probably survived a good many years so it might
be useful to explore what has changed. You haven't said
whether this is an ongoing problem or something that
happened out of the blue after 45 years.

Chuck

wrote:
On Tue, 22 Feb 2005 12:17:36 -0600, "Sail-n-Dive"
wrote:


I'm doing a bottom job on my boat that has a cast iron keel with a
centerboard slot. Most of the keel stayed rust free but the slot and the
bottom of the keel that often comes in contact with the bottom at low tide
are rusty. I'm going to chip and sand blast but I'm unsure of how to treat
the bare metal before applying the new bottom paint. Suggestions?
Quinton


Suggestion #1 - don't allow an iron keel to come in contact with the
bottom

Suggestion #2 - Several layers of epoxy covered by a hard bottom paint


Weebles Wobble
(but they don't fall down)

Pretty hard to keep the keel off of the bottom when I have only 4' of water
at my pier and we occasionally get a 3' foot tide, and when that happens my
boat and the other 20 or so in this area have no choice but to set on the
bottom until the tide lifts them back up...but what this has to do with
selecting a method for coating my keel I have not a clue!

wrote in message
...
On Tue, 22 Feb 2005 12:17:36 -0600, "Sail-n-Dive"
wrote:

I'm doing a bottom job on my boat that has a cast iron keel with a
centerboard slot. Most of the keel stayed rust free but the slot and the
bottom of the keel that often comes in contact with the bottom at low tide
are rusty. I'm going to chip and sand blast but I'm unsure of how to
treat
the bare metal before applying the new bottom paint. Suggestions?
Quinton

Suggestion #1 - don't allow an iron keel to come in contact with the
bottom

Suggestion #2 - Several layers of epoxy covered by a hard bottom paint


Weebles Wobble
(but they don't fall down)

Try Coal Tar Epoxy. Sticks like s.... to a blanket. We have a cast iron
keel and it is in good shape
Tony
S/V Ambrosia

Thanks Tony, My keel turned out to have to have 1/8" or more of scaley
rust all over and it is a real chore to get it all off. Thank goodness for
air scalers! I'm hearing several locals make the same suggestions on coal
tar epoxy.

"Lyn & Tony" wrote in message
oups.com...
Try Coal Tar Epoxy. Sticks like s.... to a blanket. We have a cast iron
keel and it is in good shape
Tony
S/V Ambrosia

In article , says...


Thanks Tony, My keel turned out to have to have 1/8" or more of scaley
rust all over and it is a real chore to get it all off. Thank goodness for
air scalers! I'm hearing several locals make the same suggestions on coal
tar epoxy.

There is only one way to get that scale off and that's with a chipping hammer.
If you grind it it just gets shiny and you think you have bare metal when all
you have is shiny scale. We know from experience. We spent several days just
whanging away with the hammer until all the scale was gone. When that is done
you will probably find that the keel is pitted. At that point you must
sandblast, if possible, or grind down to shiny metal then apply a zinc type
primer. They come in epoxy-type coatings. Then fill and fair the pits. Then
apply epoxy coating. Then apply antifouling. Also not a bad idea to mount a
couple of flat zincs directly to the iron. Then be resigned to having to do at
least the bottom of the keel again next year. Hitting bottom, though, does
keep the barnacles off.

I would never again have an iron keel.

Cast iron is quite a good metal vs. corrosion, etc.
To enhance the corrosion resistance you can boil it in very hot water
for several hours or soak the surface with a phosphoric acid mixture to
change the surface bloom of ferric oxide to ferrous oxide ... this is
the SAME process for 'blueing' iron based alloys. Why cast iron is
such a good metal for water jacket applications is that the hot water
continually turns any ferric oxide to ferrous oxide. So 'blue' the
cast iron before you coat it with anything else.



In article ,
wrote:

On Tue, 22 Feb 2005 12:17:36 -0600, "Sail-n-Dive"
wrote:

I'm doing a bottom job on my boat that has a cast iron keel with a
centerboard slot. Most of the keel stayed rust free but the slot and the
bottom of the keel that often comes in contact with the bottom at low tide
are rusty. I'm going to chip and sand blast but I'm unsure of how to treat
the bare metal before applying the new bottom paint. Suggestions?
Quinton

Suggestion #1 - don't allow an iron keel to come in contact with the
bottom

Suggestion #2 - Several layers of epoxy covered by a hard bottom paint


Weebles Wobble
(but they don't fall down)

In article ,
"Sail-n-Dive" wrote:

I'm doing a bottom job on my boat that has a cast iron keel with a
centerboard slot. Most of the keel stayed rust free but the slot and the
bottom of the keel that often comes in contact with the bottom at low tide
are rusty. I'm going to chip and sand blast but I'm unsure of how to treat
the bare metal before applying the new bottom paint. Suggestions?
Quinton



Tanzers also have cast iron keels or keel/centerboards and share info
like this on our list, http://groups.yahoo.com/group/tanzer/

Generally, we've all stripped the coal tar formulations and gone to
POR-15. The nice thing is that you don't have to get to bright metal,
just get rid of the loose flakes.

The other popular option is to barrier-coat after blasting. We did that
a dozen seasons ago and were jealous of the results reported by the POR
crowd. Had been touching up the rust spots with RustLok for a while, but
replaced most of that with POR in the past few seasons. POR has been
lasting much better in the perennial problem spots. No failure where I
did the work properly.

If I wanted to do it right, I'd chip, POR (two or 3 coats), fill, fair,
then barrier coat. That should last a decade or so (except where you
bounce).

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/

I looked at the POR website and I'll give it a try. Thanks for the info.
Quinton
"Jere Lull" wrote in message
...
In article ,
"Sail-n-Dive" wrote:

I'm doing a bottom job on my boat that has a cast iron keel with a
centerboard slot. Most of the keel stayed rust free but the slot and the
bottom of the keel that often comes in contact with the bottom at low
tide
are rusty. I'm going to chip and sand blast but I'm unsure of how to
treat
the bare metal before applying the new bottom paint. Suggestions?
Quinton



Tanzers also have cast iron keels or keel/centerboards and share info
like this on our list, http://groups.yahoo.com/group/tanzer/

Generally, we've all stripped the coal tar formulations and gone to
POR-15. The nice thing is that you don't have to get to bright metal,
just get rid of the loose flakes.

The other popular option is to barrier-coat after blasting. We did that
a dozen seasons ago and were jealous of the results reported by the POR
crowd. Had been touching up the rust spots with RustLok for a while, but
replaced most of that with POR in the past few seasons. POR has been
lasting much better in the perennial problem spots. No failure where I
did the work properly.

If I wanted to do it right, I'd chip, POR (two or 3 coats), fill, fair,
then barrier coat. That should last a decade or so (except where you
bounce).

--
Jere Lull
Xan-a-Deux ('73 Tanzer 28 #4 out of Tolchester, MD)
Xan's Pages: http://members.dca.net/jerelull/X-Main.html
Our BVI FAQs (290+ pics) http://homepage.mac.com/jerelull/BVI/