Re: [bolger] Re: Corrosion questions?
And, for the most part, rust from the inside out.
HJ
HJ
>
> Second, the last point is probably the most important. With a little
> care, steel will last a long, long time -- even in saltwater. As has
> been mentioned before, as a matter of practicality, most working
> boats are made of steel. Even those that are poorly cared for stay
> together amazingly well.
>
> YIBB,
>
> David
> --
>
>
>Derek,<snip>
>
>Phil specs this as 1/2 " galvanized (or just high end painted) and
>First, Bruce's thoughtful and informative reply richly illustrates
>None of this will make the plate last forever, it's in a tough
>enviroment, and I'd expect the fore and afte ends to be the first
>area to go as they are fequently out of the water. The wet/dry/wet
>cycle will get to them first.
>
>Best of care and luck they might outlast the plywood.
what I love about this list.
Second, the last point is probably the most important. With a little
care, steel will last a long, long time -- even in saltwater. As has
been mentioned before, as a matter of practicality, most working
boats are made of steel. Even those that are poorly cared for stay
together amazingly well.
YIBB,
David
--
C.E.P.
415 W.46th Street
New York, New York 10036
http://www.crumblingempire.com
Mobile (646) 325-8325
Office (212) 247-0296
Derek,
Phil specs this as 1/2 " galvanized (or just high end painted) and
expects it to be sacrificial, i.e. needing replacement evry so many
years due to corrosion. The main factors in it's longevity being
exposure to salt water, how often it dries out, and the integrity of
it's coating.
#1, Preventing galvanic corrosion at the screws. The screws and/or
bolts fastening it should be of a less noble alloy than the plate.
For example, don't even think of stainless steel screws, they'll stay
fine as the plate corrodes away from them. Use a cheap, steel screw
and routinely (every haul out) inspect them, remove and re-bed new
ones as required. The idea here is to make the 50 cent screws
sacrifical to the $3000 steel plate and not visa versa.
#2, Corrosion from the outside, this is a far cry from protecting 2
mm sheet metal with lots of edge seams and welds, like a modern uni-
body car, which is my area of expertise. But here goes: Prior to
first (or any subsequent touch-up) sand it well, apply a phosphoric
acid rust converter (these products chemically change rust (FEO2) to
something else (Iron Sulfite?) or some such, I'm not a chemist, but
it's not rust any more. The point here is that even after sanding to
what appears to the naked eye to be smooth shiny steel, there are
pits of rust extending down intothe body of the steel which are too
small to see, but have no trouble at all starting a new corrosion
cell right after the paint dries. Then apply a good quality oil based
primer (why add water to your now rust free steel plate) followed by
your finish coat and anti fouling (add a small bottle of cayenne
pepper to each gallon and you'll have no zebra mussels between touch
ups, but that's a different area of expertise)
#3, Crevice corrosion from between the bottom and the plate. More
difficult, but I'd hope a similar prep and painting regime would be
applied before fastening it to the bottom. Here we're depending
entirely on the first series of coatings as once it's on, it's there
for good.
#4 Haul out maintenance, inspect and replace any screws showing
corrosion, Bed them well in 3M 5200 or similar, coat the screws with
Naval Jelly before driving them in. At any and all areas of the plate
showing breaks in the paint, blisters, or scratches and wear marks:
Grind away damaged paint, sand again, treat with the phosporic acid
wash, prime and paint.
#5, Galvanic protection. Apply some sacrifical anodes to each sheet.
Replace them at haul outs as they dissolve away (saving the steel as
they go).
None of this will make the plate last forever, it's in a tough
enviroment, and I'd expect the fore and afte ends to be the first
area to go as they are fequently out of the water. The wet/dry/wet
cycle will get to them first.
Best of care and luck they might outlast the plywood.
Bruce Hector
www.rustcheckkingston.com
www.brucesboats.com
Phil specs this as 1/2 " galvanized (or just high end painted) and
expects it to be sacrificial, i.e. needing replacement evry so many
years due to corrosion. The main factors in it's longevity being
exposure to salt water, how often it dries out, and the integrity of
it's coating.
#1, Preventing galvanic corrosion at the screws. The screws and/or
bolts fastening it should be of a less noble alloy than the plate.
For example, don't even think of stainless steel screws, they'll stay
fine as the plate corrodes away from them. Use a cheap, steel screw
and routinely (every haul out) inspect them, remove and re-bed new
ones as required. The idea here is to make the 50 cent screws
sacrifical to the $3000 steel plate and not visa versa.
#2, Corrosion from the outside, this is a far cry from protecting 2
mm sheet metal with lots of edge seams and welds, like a modern uni-
body car, which is my area of expertise. But here goes: Prior to
first (or any subsequent touch-up) sand it well, apply a phosphoric
acid rust converter (these products chemically change rust (FEO2) to
something else (Iron Sulfite?) or some such, I'm not a chemist, but
it's not rust any more. The point here is that even after sanding to
what appears to the naked eye to be smooth shiny steel, there are
pits of rust extending down intothe body of the steel which are too
small to see, but have no trouble at all starting a new corrosion
cell right after the paint dries. Then apply a good quality oil based
primer (why add water to your now rust free steel plate) followed by
your finish coat and anti fouling (add a small bottle of cayenne
pepper to each gallon and you'll have no zebra mussels between touch
ups, but that's a different area of expertise)
#3, Crevice corrosion from between the bottom and the plate. More
difficult, but I'd hope a similar prep and painting regime would be
applied before fastening it to the bottom. Here we're depending
entirely on the first series of coatings as once it's on, it's there
for good.
#4 Haul out maintenance, inspect and replace any screws showing
corrosion, Bed them well in 3M 5200 or similar, coat the screws with
Naval Jelly before driving them in. At any and all areas of the plate
showing breaks in the paint, blisters, or scratches and wear marks:
Grind away damaged paint, sand again, treat with the phosporic acid
wash, prime and paint.
#5, Galvanic protection. Apply some sacrifical anodes to each sheet.
Replace them at haul outs as they dissolve away (saving the steel as
they go).
None of this will make the plate last forever, it's in a tough
enviroment, and I'd expect the fore and afte ends to be the first
area to go as they are fequently out of the water. The wet/dry/wet
cycle will get to them first.
Best of care and luck they might outlast the plywood.
Bruce Hector
www.rustcheckkingston.com
www.brucesboats.com
Hi Bruce (Hector)
You are probably aware of the hot dipped steel plate being used on some of
the AS##s going together. The plate serves as ballast and bottom armour. I
recall someone doing an AS39 this way recently.
Wearing your rust guru hat, are there any better solutions that you could
share?
Cheers
Derek
You are probably aware of the hot dipped steel plate being used on some of
the AS##s going together. The plate serves as ballast and bottom armour. I
recall someone doing an AS39 this way recently.
Wearing your rust guru hat, are there any better solutions that you could
share?
Cheers
Derek
It's Bruce Hector, wild dreamer of aircraft carriers and owner of the
Kingston Rust Check Centre. See www.rustcheckkingston for more than
you probably wanted to know about corrosion protection.
Rust on a deck fitting will usually be strictly surface pitting and
abrasion, perhaps with some rust colour bleeding on to pretty parts
where you don't want to see any. The metal itself should be too thick
to actually perforate during the life of the fitting.
Coatings on non-wear surfaces should just be painted (oil based
please on steel) over a good primer. How long it stays pretty has
everything to do with the surface preparation prior to the primer. I
don't care what Tremclad or Rustoleum says or implies in their
marketing. If you paint over any rust it will come back with a
vengeance.
Lubricate twice a year (spring and fall) with a penetrant based
corrosion inhibitor. Rust Check in Canada, Corrosion Block (available
from West Marine) in most of the USA, the rest of the world use a
light machine oil four times or more a year.
Galvanized is nice, but be aware that the zinc will wear away, is
destroyed at any weld points and causes dissimilar metal corrosion
(electrolysis) all by itself. Stainless Steel is best of course, but
there are many different grades of SS and the cheap ones still rust,
albeit slower.
The war on rust is never ending.
Kingston Rust Check Centre. See www.rustcheckkingston for more than
you probably wanted to know about corrosion protection.
Rust on a deck fitting will usually be strictly surface pitting and
abrasion, perhaps with some rust colour bleeding on to pretty parts
where you don't want to see any. The metal itself should be too thick
to actually perforate during the life of the fitting.
Coatings on non-wear surfaces should just be painted (oil based
please on steel) over a good primer. How long it stays pretty has
everything to do with the surface preparation prior to the primer. I
don't care what Tremclad or Rustoleum says or implies in their
marketing. If you paint over any rust it will come back with a
vengeance.
Lubricate twice a year (spring and fall) with a penetrant based
corrosion inhibitor. Rust Check in Canada, Corrosion Block (available
from West Marine) in most of the USA, the rest of the world use a
light machine oil four times or more a year.
Galvanized is nice, but be aware that the zinc will wear away, is
destroyed at any weld points and causes dissimilar metal corrosion
(electrolysis) all by itself. Stainless Steel is best of course, but
there are many different grades of SS and the cheap ones still rust,
albeit slower.
The war on rust is never ending.