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Red oxide paint vs hull blacking

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When we blacked some newly welded steel on the hull Years ago, I was surprised that the instructions on the bitumen tin said " paint red oxide on new steel before applying bitumen".

Years later when we dry docked to re-black, the power wash removed the blacking but couldn't budge the red oxide. So my question is why bother putting bitumen on? Why not just apply red oxide? The steel hadn't rusted or the red oxide would have flaked off with the rust.

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Trawlers where painted with Red lead .Blacking I believe is a big money making con .Alternatives are Red Oxide ,Zinger, and probably others like paint they use on pylons .Then over paint with a colour to suit for cosmetic appearances.

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If by 'Blacking' you are refereing to bichumen based products then I completely agree that they are a money making con, I've had my hull blacked by this 3 times and each time there has been rust at the waterline within the year.

 

A boat near me has had it's blacking stripped at the waterline but underneath is red oxide and although it looks a bit odd there is no rust at the waterline whatsoever. Judging by it's condition it's been like this a while too.

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I have never fully understood what benefits slapping a load of bitumen on the hull of a boat is perceived to have. What I find even more perverse is those who insist on blacking GRP boats. Why oh why?

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Possibly the reason the red oxide is in such good condition is because it was protected by the blacking.

Not sure but I doubt that red oxide has uv stabilisers and along the water line if exposed to sunlight the red oxide would not last that long, so I will continue to black my boat. I only wish I could get blacking with an anti foul additive to keep the marine life away.

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My understanding (and experience) is that Red Oxide protects the steel by a chemical and electrolytical reaction. However, it is porous.

Blacking, OTOH, is merely a coating with some abrasion resistance - to protect whatever coating there may be underneath.

 

So to my mind you need both. Indeed it might be prudent to repair any damage to the coating(s) with red oxide first followed by a top coat of bitumen.

 

I've used Admiralty spec: in the past but probably not generally available nowadays....

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Possibly the reason the red oxide is in such good condition is because it was protected by the blacking.

Not sure but I doubt that red oxide has uv stabilisers and along the water line if exposed to sunlight the red oxide would not last that long, so I will continue to black my boat. I only wish I could get blacking with an anti foul additive to keep the marine life away.

 

 

My understanding (and experience) is that Red Oxide protects the steel by a chemical and electrolytical reaction. However, it is porous.

Blacking, OTOH, is merely a coating with some abrasion resistance - to protect whatever coating there may be underneath.

 

So to my mind you need both. Indeed it might be prudent to repair any damage to the coating(s) with red oxide first followed by a top coat of bitumen.

 

I've used Admiralty spec: in the past but probably not generally available nowadays....

 

I agree with both of you. Red oxide primer is only effective as part of a coating system, which usually means a number of coats of other paint(s). Its is indeed porous and the pores need filling up with something. Blacking will fill those holes too, and thus protect the primer. The reason blacking was used on a canal boat is that hardened paint scrapes off with the inevitable contact between boat and infrastructure, but blacking just smears.

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My understanding (and experience) is that Red Oxide protects the steel by a chemical and electrolytical reaction. However, it is porous.

Blacking, OTOH, is merely a coating with some abrasion resistance - to protect whatever coating there may be underneath.

 

So to my mind you need both. Indeed it might be prudent to repair any damage to the coating(s) with red oxide first followed by a top coat of bitumen.

 

I've used Admiralty spec: in the past but probably not generally available nowadays....

I used to use both but always found the bitumen wouldn't stick well to the Red Oxide. Spencer paints technical dept advised me that it was preferable to use both. Nowadays I just use blacking purely for the better adhesion directly to the steel.

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This is probably the main reason blacking fails

 

"STEEL: Remove any rust with 60-80 grade abrasive paper and remove all dust.

PREVIOUSLY PAINTED SURFACES: Sand surface with 120-150 grade (grit) paper and remove all dust.
Method Apply 2-3 coats (spray) or 4-5 coats (brush)."

 

and then 3 days to dry. I don't know anyone who does 5 coats and then leaves it for 3 days to dry.

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My understanding (and experience) is that Red Oxide protects the steel by a chemical and electrolytical reaction. However, it is porous.

Blacking, OTOH, is merely a coating with some abrasion resistance - to protect whatever coating there may be underneath.

 

So to my mind you need both. Indeed it might be prudent to repair any damage to the coating(s) with red oxide first followed by a top coat of bitumen.

 

I've used Admiralty spec: in the past but probably not generally available nowadays....

 

That's exactly what I do by way of maintaining above water surface at least, for cosmetic as well as corrosion reasons. To speed the process I use an angle grinder fitted with sanding disc, then treat any bare metal surfaces with Kurust, especially if there is deeper rust. Then two coats of red oxide followed by bitumen paint. As my gunnels are red oxide coloured finish I get to touch up any attrition in that area as well.

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Possibly the reason the red oxide is in such good condition is because it was protected by the blacking.

Not sure but I doubt that red oxide has uv stabilisers and along the water line if exposed to sunlight the red oxide would not last that long, so I will continue to black my boat. I only wish I could get blacking with an anti foul additive to keep the marine life away.

Why not just use a black antifoul paint instead of blacking?

 

(Assumes of course you are starting with a fresh non blacked hull)

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Why not just use a black antifoul paint instead of blacking?

 

(Assumes of course you are starting with a fresh non blacked hull)

I think it will be a sad day when antifoulingis in general use on the inland waterways.

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Why not just use a black antifoul paint instead of blacking?

 

(Assumes of course you are starting with a fresh non blacked hull)

Because bitumen tends to smear and spread and to a degree self heal litle scratches. For a canal boat going into narrow locks with just a couple of inches clearance each side the odd bump and scrape is inevitable and there are no fenders to reduce the rubbing when filling and emptying the lock.

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I think it will be a sad day when antifoulingis in general use on the inland waterways.

It already is.

Because bitumen tends to smear and spread and to a degree self heal litle scratches. For a canal boat going into narrow locks with just a couple of inches clearance each side the odd bump and scrape is inevitable and there are no fenders to reduce the rubbing when filling and emptying the lock.

Get a soft antifoul and it will with stand the odd knock and scrape.

 

Bumps and scrapes above the waterline can be touched in much the same as with bitumen based products.

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On the broads maybe, but the percentage on the canals is not as high. The Broads are trying to reduce its use.

Not just the Broads. Anywhere where there are GRP boats. By far the most common hull paint for GRP boats be that coastal or inland is antifoul paint.

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Not just the Broads. Anywhere where there are GRP boats. By far the most common hull paint for GRP boats be that coastal or inland is antifoul paint.

OK I'm board at the moment just like you who is at work. What is the percentage of cruisers to steel narrowboats on the canals?

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OK I'm board at the moment just like you who is at work. What is the percentage of cruisers to steel narrowboats on the canals?

No idea what is the percentage of cruisers to steel narrowboats on the canals as a whole?

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I was going to say, the term 'red oxide' is likely misleading as all it really means is theres some iron oxide in there as a pigment. Certainly very few (no high street brands) red coloured primers have any lead oxide in them at all these days as per 'red lead' or years gone by.

 

There are plenty of good quality, durable and long lasting, blacking products out there, but a lot choose to use alternatives which perform much less well.

 

 

 

Daniel

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I always wonder why people find it necessary to scrape most of the bitumen off before re-blacking. Every two or three years I just put yet another coat of bitumen over what's already there, building up a nice thick layer of protection.

It means, of course, that the rivets no longer show very prominently, but there's never any rust at the waterline.

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In our early boating days, knowing no better, we used Zinc Chromate primer under the blacking. This gave an interesting Bright Yellow and Black striped effect as the blacking wore away...

 

Never again - but Zinc Chromate primer does stick well.......but probably not considered to be the best thing to use these days, given that it is now considered to be highly toxic and carcinogenic.

 

Chris G

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but Zinc Chromate primer does stick well.......but probably not considered to be the best thing to use these days, given that it is now considered to be highly toxic and carcinogenic.

 

Chris G

Oh well, the taxpayer will be pleased with the reduction in the naval pensions budget - everything used to get a coat of that!

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>> hardened paint scrapes off with the inevitable contact between boat and infrastructure, but blacking just smears. <<

 

 

Because bitumen tends to smear and spread and to a degree self heal litle scratches. For a canal boat going into narrow locks with just a couple of inches clearance each side the odd bump and scrape is inevitable and there are no fenders to reduce the rubbing when filling and emptying the lock.

 

There's an echo in here ...

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