Coal tar for bottom of steel hull?
 

Hi,

I'm considering buying a houseboat with a steel bottom. New steel
was put on 4 years ago, and treated with coal tar epoxy, supposedly.
I was told that the coal tar treatment will last for a long time. Can
anyone tell me if the coal tar treatment is really good for a long time,
like 30 years or something? If it is, then why doesn't everyone use
it? It it's not, then how long is it good for, what to do, and when, in
the future?

Thanks for any help!
David

When I worked as a pile driver we coated steel to be under water with a
product called Bitumastic.
Worked for many years submerged 365.
Though not pretty tars can be great coatings.
If it interests you and you have the time do some tests.

David, Its the epoxy word thats significant. Coal Tar Epoxy is used to coat
steel pipes and equipment in sewage treatment plants so you may gather it
can withstand all sorts of acidic substances and has a long life. However, I
don't know how it withstands the wear caused by rushing through water.
I have no experience of that.
Wilf

Coal tar has been in use in the Dutch canals for a 100 years successfully.
It is still in use. Your risk to corrosion is on the inside, not the
outside. Even there tar works very well unless it is exposed to oil or fuel.
I have seen examples of steel hulls immersed in salt water unpainted and
suffer 0 corrosion except at the air/water margin. Condensation on the
inside is a whole different matter. There the best protection is urethane
foam above the water line and tar below.
Steve
wrote in message
...
Hi,

I'm considering buying a houseboat with a steel bottom. New steel
was put on 4 years ago, and treated with coal tar epoxy, supposedly.
I was told that the coal tar treatment will last for a long time. Can
anyone tell me if the coal tar treatment is really good for a long time,
like 30 years or something? If it is, then why doesn't everyone use
it? It it's not, then how long is it good for, what to do, and when, in
the future?

Thanks for any help!
David

On Mon, 21 Feb 2005 21:50:56 +0100, "Steve Lusardi"
wrote:

Condensation on the
inside is a whole different matter. There the best protection is urethane
foam above the water line and tar below.

Wish more people did that. I've seen steel hulls with everything below
the cabin sole foamed in, and it seems to essentially trap moisture
and makes a nice damp sponge...with predictable results.

Can you coal tar the entire interior hull and then foam waterline to
hull joint? In other words, will ureathane foam stick to tarred steel?
And is there any benefit to this?

R.

Here in Thailand it is widely used on steel boats and boats with cast
iron keels ( our 42' ketch) lasts for many years especially when
overcoated with anti-foul. Coal Tar Epoxy is as the name suggests - an
epoxy.

Tony
S/V Ambrosia

Yes, that is common practise. Keep in mind that epoxy paints work well if
not exposed to sunlight. Very poor UV protection.
Steve

"rhys" wrote in message
...
On Mon, 21 Feb 2005 21:50:56 +0100, "Steve Lusardi"
wrote:

Condensation on the
inside is a whole different matter. There the best protection is urethane
foam above the water line and tar below.

Wish more people did that. I've seen steel hulls with everything below
the cabin sole foamed in, and it seems to essentially trap moisture
and makes a nice damp sponge...with predictable results.

Can you coal tar the entire interior hull and then foam waterline to
hull joint? In other words, will ureathane foam stick to tarred steel?
And is there any benefit to this?

R.

coal tar epoxy is unhealthy, 1970s type coating with all sorts of problems.
Use instead modern coal tar equivalents that don't use coal tar as an epoxy
additive


paul oman
progressive epoxy polymers





Steve Lusardi wrote:

Yes, that is common practise. Keep in mind that epoxy paints work well if
not exposed to sunlight. Very poor UV protection.
Steve

"rhys" wrote in message
...
On Mon, 21 Feb 2005 21:50:56 +0100, "Steve Lusardi"
wrote:

Condensation on the
inside is a whole different matter. There the best protection is urethane
foam above the water line and tar below.

Wish more people did that. I've seen steel hulls with everything below
the cabin sole foamed in, and it seems to essentially trap moisture
and makes a nice damp sponge...with predictable results.

Can you coal tar the entire interior hull and then foam waterline to
hull joint? In other words, will ureathane foam stick to tarred steel?
And is there any benefit to this?

R.




--


"Living on Earth is expensive, but it does include
a free trip around the Sun every year."

i agree with steve that u should pay attention to the inside.
1. for the steel vessel, if the do the full blasting prior to painting,
then the result is superior. dont forget the most important thing-
blasting. after blasting u should paint the marine primer then
undercoat and then coal tar expoxy and then to avoid marine growth, u
should have the antifouling painted.
2. Usually boat owner will dock their vessel 2 to 3 years for
inspection of the underwater hull and do some repair that have to be
done during docking like inspection/repair of the seawater intake valve
or strainer. u cant repair this item when the vessel is in the water.
3. coal tar expoxy in my experience is a very good paint and though
there are many new paint at the market now but for me, if the price is
reasonable, u still can use this paint.
4. if your vessel is stationary there, not moving very often where u
will not scratch your underwater hull by those floating wood or
rubbish, then the coal tar expoxy will last for many years but i am not
sure it will last 30 years. if u do the blasting and follow the paint
scheme, then the underwater hull really may last for many years.
5. In my country many boat owners like to use coal tar because it is
cheaper then other new paint system.
hope this will help.