Gloss paint on underwater hull

[jenevers]

Anyone ever had any success in painting their underwater hull in gloss paint?

I used bitumen last time and, due to a big diesel slick in the canal a few weeks later from some unknown source, all the bitumen on the waterline came off. Ooh I was so happy!

I'm not going to gave the hull grit blasted/2 packed next time so wondered if bog standard gloss paint would be worth trying instead of bitumen.

 

[OldGoat]

Comastic is said to be resistant to diesel spills. Gloss paint chips too easily.

 

[Neil2]

If you have standard blacking on the hull you will have to have it all grit blasted anyway, so you might as well use a recommended product.

I believe some have used standard gloss paint underwater with some success but it's not designed for constant immersion in water.

[Peter-Bullfinch]

Many of the boats from, I think the Lymm Cruising Club on the Bridgewater, seem to have gloss painted hills. Few locks in this area though so maybe they get k ocked around less.

[nicknorman]

If you have had bitumen on it, gloss paint won't stick to it. Gloss paint also won't stick to the rusty bits at the waterline. It's a non-starter unless you are going back to bare metal and even then, a bad idea. We bit the bullet and had our boat grit blasted and 2-packed and are very pleased with the result. I'd never go back to ordinary blacking.

[Dr Bob]

Gloss paint will not work.

i) it is not designed for immersion so water will penetrate it and so the rusting will continue. It is very poor for water transmission in immersion so this will happen in a short space of time.

ii) worse.....the adhesion of the paint to the existing blacking or rust will be very poor. This means as soon as rust starts to form, it will push the coating off the surface and thus more rust forms. Not a lot of things will stick to blacking which is why you need to grit blast to get the residue off. Any scrape will become a point at which rust will form and this will then cut under the coating (due to the poor adhesion) giving large areas of corrosion.

If you are not grit blasting then another coat of blacking is the best. If you do blast, then you have a choice of many coatings.

Think about it, if gloss paint worked, why wouldnt everyone be using it? It doesn't. So they are not.

[Dylan]

2 hours ago, nicknorman said:

If you have had bitumen on it, gloss paint won't stick to it. Gloss paint also won't stick to the rusty bits at the waterline. It's a non-starter unless you are going back to bare metal and even then, a bad idea. We bit the bullet and had our boat grit blasted and 2-packed and are very pleased with the result. I'd never go back to ordinary blacking.

Likewise.

2 hours ago, Peter-Bullfinch said:

Many of the boats from, I think the Lymm Cruising Club on the Bridgewater, seem to have gloss painted hills. Few locks in this area though so maybe they get k ocked around less.

Is that the stuff that is often blue? I have seen this and wondered if it was an antifouling.

[peterboat]

When I had my first boat, I went for my first blacking to a drydock near Macclesfield, the boat in before me was gloss black painted, it was over 30 years old and the bottom in pristine condition. I dont know what paint he used only that he scotched it off after power washing it then gave it 2 coats. It had never been blacked and was red leaded where any damage was found before painting, it was I have to say in far better condition than mine underneath................................

Edited August 27, 2017 by peterboat

[blackrose]

29 minutes ago, peterboat said:

When I had my first boat, I went for my first blacking to a drydock near Macclesfield, the boat in before me was gloss black painted, it was over 30 years old and the bottom in pristine condition. I dont know what paint he used only that he scotched it off after power washing it then gave it 2 coats. It had never been blacked and was red leaded where any damage was found before painting, it was I have to say in far better condition than mine underneath................................

But you only saw the last coats of paint and you don't know what had been done before that during the previous decades to protect the hull.

13 hours ago, Dr Bob said:

Gloss paint will not work.

i) it is not designed for immersion so water will penetrate it and so the rusting will continue. It is very poor for water transmission in immersion so this will happen in a short space of time.

ii) worse.....the adhesion of the paint to the existing blacking or rust will be very poor. This means as soon as rust starts to form, it will push the coating off the surface and thus more rust forms. Not a lot of things will stick to blacking which is why you need to grit blast to get the residue off. Any scrape will become a point at which rust will form and this will then cut under the coating (due to the poor adhesion) giving large areas of corrosion.

If you are not grit blasting then another coat of blacking is the best. If you do blast, then you have a choice of many coatings.

Think about it, if gloss paint worked, why wouldnt everyone be using it? It doesn't. So they are not.

Yes, I really don't know why some people want to use products that just aren't designed for the job? 

Edited August 27, 2017 by blackrose

[Bee]

I painted the above water part with ordinary gloss paint once, after 12 months it looked as though I had steered into every lock wall, bridge hole, tree and stick on the system. Covered the whole lot up with bituminous paint and am no longer embarrassed. (Sigma two pack underwater though)

[DandV]

If you are going to the expense of grit blasting then use a paint system produced by a reputable manufacturer designed for continuous immersion. They are expensive but ship and oil rig owners as well as mere narrowboaters find they are the most economic system over their life. Azko Nobel market the International brand Interzone 954 but other major suppliers will have comparable products as it is such a large market

 

 

 

 

 

 

[Richard10002]

Last time I was out for blacking the chap on the boat next to me used Primocon followed by a light blue antifoul... which is what I used to use on my seagoing boat. Knowing what antifoul used to cost me, blacking is clearly much less expensive, which is probably the reason we do it.

[Neil2]

I don't believe it's the cost driven, when I talk to other boaters the main reason people give for continuing blacking with bitumen based products is because to use anything else involves grit blasting the hull and it's too much hassle compared with simply lifting or dry docking.  Also I suspect many owners are scared of finding out what their hull really looks like under all that crud.     

[Naughty Cal]

20 hours ago, Richard10002 said:

Last time I was out for blacking the chap on the boat next to me used Primocon followed by a light blue antifoul... which is what I used to use on my seagoing boat. Knowing what antifoul used to cost me, blacking is clearly much less expensive, which is probably the reason we do it.

How much is blacking?

One 3 litre can of antifoul costs us £45 and is enough to give our boat 2 full coats and a third around the waterline.

[rusty69]

13 minutes ago, Naughty Cal said:

How much is blacking

Expensive for what it is, about 35 quid for 5 litres of Rylards 

Edited August 28, 2017 by rusty69

[jenevers]

My experience is that when I had some new plating done under the waterline, I red oxided the new Steel before applying bitumen (as per the instructions on the bitumen tin!). Years later whenever I blast the hull for re-bitumening, the red oxide is still there and cannot be budged. So, I thought maybe black gloss on top of the red oxide would be more resistant to diesel in the water than bitumen.

 

[peterboat]

23 hours ago, blackrose said:

But you only saw the last coats of paint and you don't know what had been done before that during the previous decades to protect the hull.

Yes, I really don't know why some people want to use products that just aren't designed for the job? 

True, but he had owned the boat from new, and this was the process he carried out every couple of years to protect his boa,t and his boat was in pristine condition

[Bloomsberry]

11 hours ago, Neil2 said:

I don't believe it's the cost driven, when I talk to other boaters the main reason people give for continuing blacking with bitumen based products is because to use anything else involves grit blasting the hull and it's too much hassle compared with simply lifting or dry docking.  Also I suspect many owners are scared of finding out what their hull really looks like under all that crud.     

I DIY epoxied my boat last year (well, the important parts anyway) without gritblasting using a rotary blaster mounted in a drill.

 

This was over 12 months ago and it all appears to be still intact including the entire waterline which only survived a few months when using normal bitumen.

[Dr Bob]

2 hours ago, jenevers said:

My experience is that when I had some new plating done under the waterline, I red oxided the new Steel before applying bitumen (as per the instructions on the bitumen tin!). Years later whenever I blast the hull for re-bitumening, the red oxide is still there and cannot be budged. So, I thought maybe black gloss on top of the red oxide would be more resistant to diesel in the water than bitumen.

 

That is a good question......but to answer it, you need to understand a bit about 'paints'.

Apologies for a long post but let me give you some background to help you make a judgement (and also apologies for 'dumbing this down a bit').

Coatings to protect steel from corrosion work in one of two ways.

i) Corrosion takes place when water and oxygen get to the steel surface. You can stop corrosion if you stop the water/O2 getting to the steel. The first class of coatings therefore are designed to do this. They tend to be heavily crosslinked materials (ie epoxies) and are usually 2 pack systems where when the 2 packs are mixed a cross linking reaction takes place and turns a liquid into an almost impenetrable solid. They are formulated with fillers and other additives to improve resistance to permeability and adhesion.

Coatings of this type also have to have excellent adhesion to the surface otherwise if there is a defect in the coating or you get a scratch, water and oxygen can get onto the surface and then propagate under the coating where the adhesion is poor. This then links to surface preparation and a good grit blast to SA2.5 (a Swedish standard that the paint industry use) is the best, but many 2 pack systems are modified to allow some rust or moisture. In general though all loose rust and surface contaminants (ie oil or existing blacking) must be removed.

ii) The second way of protecting the surface is to apply a primer that has corrosion passifying properties ie a zinc rich primer. In this case the 'metal' (or more likely metal oxide) in the primer will protect the steel and stop corrosion. These are often single pack coatings but can be 2 pack. If 2 pack they will be more crosslinked and therefore less permeable to water/O2.

So how do you choose a coating? For painting top sides you can choose either of the two ways to protect the steel or combine the both. Top coat gloss paint is a single pack so will not crosslink heavily but high crosslinking is not needed for a top coat. These are usually acrylic type paints that crosslink (lightly) via reaction with the oxygen (or maybe moisture dependent on the formulation).

For underwater use (or more difficult the splash zone – ie the water line), the same applies, either use a system that is largely impermeable and has good adhesion or one that passivates well. Further back up the thread someone commented on a boat with red lead painted with a gloss coat. This is the way a lot of underwater applications were done and it does work to some extent but the gloss coat is very limited. The key here though is the word 'Red Lead'. Red Lead was the best coating ever produced. It worked. Problem is it is now banned. Nothing has replaced it. Nothing comes near its performance. 'Red Oxide' is nowhere near as good. I can quite imagine a boat with red lead and then painted with a simple top coat (and touched up every few years working). A better top coat would make it even better.

The problem today is you cannot use red lead. You are therefore left with the choice of a good passifier coating , ie the zinc treatments plus a 2 pack top coat or a good 2 pack primer/top coat (which really means an epoxy or epoxy coat tar) if you want to avoid blacking. If you go to the trouble of preparing the surface for the zinc treatment (or zinc rich coating) then you may as well use a 2 pack top coat.

Blacking is the cheap way to do it and works by sticking well and providing a couple of years protection again permeation. Problem is, once its on, it is then difficult to get any other coating to adhere well.

In all of the above I have ignored the need for coatings to be tough, flexible and not brittle. That is another story.

Red Lead was phased out in the early seventies so most of the guys who knew how to formulate the paints are now dead or forgotten how to do it. It is not difficult to knock up 25 litres – all the raw materials are available and you just need a good high shear mixer.

Your idea of gloss over a red oxide primer may give some lifetime but if you spend the time getting the surface clean enough to get the red oxide on then why not put a more water resistant coating on.

All good stuff but my boat is out the water this week being blacked. I'm new to steel boats so dont know enough about long term performance to pay out for a grit blast and 2 pack system yet. My experience in the paint industry is that surface prep and application are just as important as the paint used so picking the right contractor is vital. Red Lead paint was almost idiot proof. Today's 2 packs aren’t. Maybe in 2 years I will be grit blasting it.

[WotEver]

Great article about Red Lead paint dating from 1936:

http://www.dtic.mil/get-tr-doc/pdf?AD=ADA951446

[jenevers]

4 hours ago, Dr Bob said:

That is a good question......but to answer it, you need to understand a bit about 'paints'.

Apologies for a long post but let me give you some background to help you make a judgement (and also apologies for 'dumbing this down a bit').

Coatings to protect steel from corrosion work in one of two ways.

i) Corrosion takes place when water and oxygen get to the steel surface. You can stop corrosion if you stop the water/O2 getting to the steel. The first class of coatings therefore are designed to do this. They tend to be heavily crosslinked materials (ie epoxies) and are usually 2 pack systems where when the 2 packs are mixed a cross linking reaction takes place and turns a liquid into an almost impenetrable solid. They are formulated with fillers and other additives to improve resistance to permeability and adhesion.

Coatings of this type also have to have excellent adhesion to the surface otherwise if there is a defect in the coating or you get a scratch, water and oxygen can get onto the surface and then propagate under the coating where the adhesion is poor. This then links to surface preparation and a good grit blast to SA2.5 (a Swedish standard that the paint industry use) is the best, but many 2 pack systems are modified to allow some rust or moisture. In general though all loose rust and surface contaminants (ie oil or existing blacking) must be removed.

ii) The second way of protecting the surface is to apply a primer that has corrosion passifying properties ie a zinc rich primer. In this case the 'metal' (or more likely metal oxide) in the primer will protect the steel and stop corrosion. These are often single pack coatings but can be 2 pack. If 2 pack they will be more crosslinked and therefore less permeable to water/O2.

So how do you choose a coating? For painting top sides you can choose either of the two ways to protect the steel or combine the both. Top coat gloss paint is a single pack so will not crosslink heavily but high crosslinking is not needed for a top coat. These are usually acrylic type paints that crosslink (lightly) via reaction with the oxygen (or maybe moisture dependent on the formulation).

For underwater use (or more difficult the splash zone – ie the water line), the same applies, either use a system that is largely impermeable and has good adhesion or one that passivates well. Further back up the thread someone commented on a boat with red lead painted with a gloss coat. This is the way a lot of underwater applications were done and it does work to some extent but the gloss coat is very limited. The key here though is the word 'Red Lead'. Red Lead was the best coating ever produced. It worked. Problem is it is now banned. Nothing has replaced it. Nothing comes near its performance. 'Red Oxide' is nowhere near as good. I can quite imagine a boat with red lead and then painted with a simple top coat (and touched up every few years working). A better top coat would make it even better.

The problem today is you cannot use red lead. You are therefore left with the choice of a good passifier coating , ie the zinc treatments plus a 2 pack top coat or a good 2 pack primer/top coat (which really means an epoxy or epoxy coat tar) if you want to avoid blacking. If you go to the trouble of preparing the surface for the zinc treatment (or zinc rich coating) then you may as well use a 2 pack top coat.

Blacking is the cheap way to do it and works by sticking well and providing a couple of years protection again permeation. Problem is, once its on, it is then difficult to get any other coating to adhere well.

In all of the above I have ignored the need for coatings to be tough, flexible and not brittle. That is another story.

Red Lead was phased out in the early seventies so most of the guys who knew how to formulate the paints are now dead or forgotten how to do it. It is not difficult to knock up 25 litres – all the raw materials are available and you just need a good high shear mixer.

Your idea of gloss over a red oxide primer may give some lifetime but if you spend the time getting the surface clean enough to get the red oxide on then why not put a more water resistant coating on.

All good stuff but my boat is out the water this week being blacked. I'm new to steel boats so dont know enough about long term performance to pay out for a grit blast and 2 pack system yet. My experience in the paint industry is that surface prep and application are just as important as the paint used so picking the right contractor is vital. Red Lead paint was almost idiot proof. Today's 2 packs aren’t. Maybe in 2 years I will be grit blasting it.

Excellent information.

Thanks for taking so much time and trouble.

41 minutes ago, WotEver said:

Great article about Red Lead paint dating from 1936:

http://www.dtic.mil/get-tr-doc/pdf?AD=ADA951446

Those were the days!

[Dr Bob]

1 hour ago, WotEver said:

Great article about Red Lead paint dating from 1936:

http://www.dtic.mil/get-tr-doc/pdf?AD=ADA951446

That's an interesting article. There we go, we can now make our own red lead paint!

Back in the '30s though, they were using linseed oil as the binder resin which subsequently took a week to cure! In the article they are saying over coat in 4 days!!!! By the 60's the industry had changed over to using Alkyd resins (which are basically polyesters with fatty acids to assist in crosslinking) which cured (crosslinked) much faster. The red led powder was the important bit. I did a quick search and you can buy red lead powder in the UK.