Hull painting with Zinka

[dmr]

5 hours ago, Dr Bob said:

Barrier coating work by being good at 1, 2, and 3  but not 4.

Pacifying coatings work by 4.

These are two completely different mechanisms to prevent corrosion.

For barrier coatings ie your 2 pack epoxy, they stop water getting to the surface so no corrosion. If you get a scrape, then the exposed surface will rust but because the adhesion of the coating is very good,  the rust will not undercut it and force the coating off. This is where epoxies are so much better than other coatings as the adhesion is vastly superior. Less adhesion and the coating would be undercut by the rust and the rust patches would spread. If you get a scratch on a pacifying coating then the rust cant spread as the active ingredients will stop the rust formation.

Red lead was the best pacifying coating but I am not sure if anything today can come close. Not a clue what is in red oxide but it is not lead and it doesnt do half the job.

Is zinc (hot sprayed, cold applied) any good? I dont know. Hot dipped yes, but difficult to dip a boat.

I do know that a good 2 pack epoxy applied to a good surface (SA2.5) should be good for 10 years+ as long as scrapes and bashes are touched up regularly. My worry over going the epoxy route is the question of whether the yard do it properly. Painting in the UK is not easy with our weather. I spent may weeks out on site in the 80's watching our tolerant epoxies dry....and even with the best will in the world it is difficult to get the surface right and to have the right temperature, sun and wind for painting.

The world does not have a good tolerant corrosion protection coating that will last 10 years any more. 2 pack epoxy is probably the best for an SA2.5 surface. Maybe in the next 5 years or so, zinga will emerge as the best solution. I cant see any evidence at the moment that any one system is better than another except we know 2 pack epoxies do work.

 

As always a very informative and interesting post from you,though based on personal experience I want to question a couple of things.

 

The "undercut by rust" is interesting. I sometimes get very small holes in my paint (I assume these are stone chips though some bugger did shoot at us last winter) and whenever I grind these out with my Dremmel I find the rust has spread a little way below the paint. I had always assumed the rust was propagating through the steel itself but you suggest its running below the paint due to incomplete bonding????? I think you infer that epoxy should not do this but in fact a known weakness of epoxy is that a local sheet will actually lift right off the steel. This has happened on my front deck around the water tank inception hatch, I will try to take a photo. Ditchcrawler believes this is a potential issue with epoxy coatings in water tanks too where the boat gets some bangs. I have also seen examples where the galvanising has lifted off steel as a whole sheet as the water runs between the steel and zinc. As rust gives a volume expansion surely even epoxy can not avoid lifting adjacent to a scratch and so letting rust propagate?????

 

A question......

Will 2 pack last much longer than ten years if it is periodically repainted, or does it chemically decompose after about ten years?

 

..............Dave

 

 

[peterboat]

16 minutes ago, ditchcrawler said:

Did you use airless spray for that

No a quality spray gun, I was using a primer gun as the zinga is quite thick all the info comes from them what you need mixing ratios etc, I found it easy enough apart from the weight of the gun full, it really is 96% zinc and is very heavy to say the least

[Dr Bob]

Just now, dmr said:

 

 

Will 2 pack last much longer than ten years if it is periodically repainted, or does it chemically decompose after about ten years?

 

 

 

I dont think it will chemically decompose. The effect of UV might cleave a few carbon-carbon or carbon-oxygen bonds but that's not really decomposition.

It will however cause it to be more brittle so it will be more prone to micro cracking from thermal or mechanical shock. Micro cracks will allow water then to get to the surface where it can start corroding the steel, but the good adhesion stops the corrosion undercutting the coating. The actual water transmission or adhesion properties are unlikely to change much.

Bottom line then IF the existing coating is stuck very well - use a pen knife to assess - then periodic repainting is good to overcome the negatives of microcracking.  If there is any sign the adhesion is failing then I would take it all off and start again on grit blated steel. Maybe after 20 years and one full overcoat I would blast it all off.

 

[dmr]

1 minute ago, Dr Bob said:

I dont think it will chemically decompose. The effect of UV might cleave a few carbon-carbon or carbon-oxygen bonds but that's not really decomposition.

It will however cause it to be more brittle so it will be more prone to micro cracking from thermal or mechanical shock. Micro cracks will allow water then to get to the surface where it can start corroding the steel, but the good adhesion stops the corrosion undercutting the coating. The actual water transmission or adhesion properties are unlikely to change much.

Bottom line then IF the existing coating is stuck very well - use a pen knife to assess - then periodic repainting is good to overcome the negatives of microcracking.  If there is any sign the adhesion is failing then I would take it all off and start again on grit blated steel. Maybe after 20 years and one full overcoat I would blast it all off.

 

 

We had two full new coats put  on after 3 years, so extrapolating to 20 years it will have had 14 new coats!!!, I wonder what the limit is?? maybe we will be too fat to fit through the locks  

 

The international only comes in very big pots so its either two complete coats or throw a whole lot away (at £400 a go). I am going to investigate changing to Jotun this year as this comes in smaller pots, this will depend upon if Jotun think its ok to overcoat a different brand of epoxy.

 

..................Dave

 

[Fly Navy]

Compared to how much for standard bitumen blacking?

[matty40s]

13 minutes ago, Fly Navy said:

Compared to how much for standard bitumen blacking?

£120 ish a 20l tin trade price....went up 6 times last year.

[Captain Pegg]

10 hours ago, Stilllearning said:

That must be an interesting system to use, as zinc melts at 419.5 deg Celsius.

I doubt it is because it's all highly controlled in a purpose built facility. It's also not particularly hot for metalwork since zinc has a low melting point compared to common engineering metals. The zinc leaving the spray nozzle will cool rapidly and then hit steel at ambient temperature, for which reason it absolutely does not bond like hot dip galvanising. That requires the steel to act as a heat sink and it's the transfer of the right amount of energy that produces the chemical bonding between zinc and steel.

 

The advantage of going to a facility like Debdale is that they have the set up to get the preparation and application spot on. That's more important than the system you choose.

 

JP

[Dr Bob]

3 hours ago, dmr said:

 

We had two full new coats put  on after 3 years, so extrapolating to 20 years it will have had 14 new coats!!!, I wonder what the limit is?? maybe we will be too fat to fit through the locks  

 

The international only comes in very big pots so its either two complete coats or throw a whole lot away (at £400 a go). I am going to investigate changing to Jotun this year as this comes in smaller pots, this will depend upon if Jotun think its ok to overcoat a different brand of epoxy.

 

..................Dave

 

Dave,

I'm surprised you needed a full coat after 3 years. My experience is painting things that dont move, tanks, splash zone legs of platforms, refinery kit etc. 10 years is typical between recoats. Ok, need to touch up damage but only small areas. I would only touch up and not do a full coat. With multiple full coats you are going to build up a significant thickness which then is a problem as it gets hard and brittle and could then break off more easily. If you put on say 500 microns dry film thickness (dft) then with repaints in 10 years you will have 2mm  dft of epoxy which is not good.  If you are pulling the boat out soon, only touch up damage. Maybe a zinga type coating would be more suitable for boats that are getting lots of damage as they will suffer less - the coatings will be more 'pliant' and adhesion and coating fracture is not as important, as they work by pacifying the surface.

I think that is subconsciously why I am happy to slap on cheapo blacking every 2 years.

Jotun (along with International) are one of the top coating formulators.  Unless you are using a wierd International coating then I am sure Jotun will think it ok. Ring them up. Both Jotun and International tech service guys know what they are talking about.

14 minutes ago, Captain Pegg said:

 

.......is that they have the set up to get the preparation and application spot on. That's more important than the system you choose.

 

 

Absolutely.

[dmr]

36 minutes ago, Dr Bob said:

Dave,

I'm surprised you needed a full coat after 3 years. My experience is painting things that dont move, tanks, splash zone legs of platforms, refinery kit etc. 10 years is typical between recoats. Ok, need to touch up damage but only small areas. I would only touch up and not do a full coat. With multiple full coats you are going to build up a significant thickness which then is a problem as it gets hard and brittle and could then break off more easily. If you put on say 500 microns dry film thickness (dft) then with repaints in 10 years you will have 2mm  dft of epoxy which is not good.  If you are pulling the boat out soon, only touch up damage. Maybe a zinga type coating would be more suitable for boats that are getting lots of damage as they will suffer less - the coatings will be more 'pliant' and adhesion and coating fracture is not as important, as they work by pacifying the surface.

I think that is subconsciously why I am happy to slap on cheapo blacking every 2 years.

Jotun (along with International) are one of the top coating formulators.  Unless you are using a wierd International coating then I am sure Jotun will think it ok. Ring them up. Both Jotun and International tech service guys know what they are talking about.

Absolutely.

Thanks

 

As I have said, our boat moves a lot, so does get some scrapes. The International only comes in huge pots so this gives two full coats or a lot of wasteage, but it also fades from almost black to medium grey over a year or two so just touching upthe scrapes would look a right mess. What you say does give more reason to switch to Jotun as then at worse its one full coat each time.

 

I suppose after about 10 years it might be time to take it all off and start again which is why I would like to know more about Zinc. Trouble with Zinc is the touch up process  will need new zinc plus whatever goes over it. I expect shot blasting epoxy back to bare metal will be a lot more tedious (expensive?) than just taking old blacking off.

 

After getting the boat done in epoxy then taking it a few years later I would never go back to ordinary blacking, the epoxy was still perhaps 98% good but when we used to do ordinary blacking there would be a lot of bare metal and rust.

 

...............Dave

 

[Fly Navy]

So on face value, to coat a 50 footer with Zinca, would cost about £600(does this include grit blasting as well?) with some serious left overs, but would probably last around 10 years?

Alternatively - Bitumen every 2 years (maybe stretch to 3 dependent on environmental factors) @ £120 a pop (presumably this is done by the owner not a company?).

That would mean 5 times cheaper going down the bitumen route. This equates - lo and behold - to a period of 10 (ish) years too!!!

 

So after 10 years have passed - monetarily - not much in it.

 

However, if you owned a boat with a zinca hull - how often would you haul it out for inspection?  And now the additional costs of haul out/in come into play.

 

I think I liked the idea initially of the Zinca hull because of its superior properties compared to good old tar (bitumen). Paint it on and forget it.  But it's not that simple is it?  Curiosity would persuade me to haul the boat out every 2-3 years anyway to get that comfy feeling that nothing sinister is ongoing under the surface.

 

Views?

Edited February 28, 2019 by Fly Navy

[peterboat]

24 minutes ago, Fly Navy said:

So on face value, to coat a 50 footer with Zinca, would cost about £600(does this include grit blasting as well?) with some serious left overs, but would probably last around 10 years?

Alternatively - Bitumen every 2 years (maybe stretch to 3 dependent on environmental factors) @ £120 a pop (presumably this is done by the owner not a company?).

That would mean 5 times cheaper going down the bitumen route. This equates - lo and behold - to a period of 10 (ish) years too!!!

 

So after 10 years have passed - monetarily - not much in it.

 

However, if you owned a boat with a zinca hull - how often would you haul it out for inspection?  And now the additional costs of haul out/in come into play.

 

I think I liked the idea initially of the Zinca hull because of its superior properties compared to good old tar (bitumen). Paint it on and forget it.  But it's not that simple is it?  Curiosity would persuade me to haul the boat out every 2-3 years anyway to get that comfy feeling that nothing sinister is ongoing under the surface.

 

Views?

600 squids for material I was clear in that blasting is extra and varies greatly around the country, I have done the checking business and now am going to extend the drydocking to four years or so

[Dr Bob]

8 hours ago, Fly Navy said:

So on face value, to coat a 50 footer with Zinca, would cost about £600(does this include grit blasting as well?) with some serious left overs, but would probably last around 10 years?

Alternatively - Bitumen every 2 years (maybe stretch to 3 dependent on environmental factors) @ £120 a pop (presumably this is done by the owner not a company?).

That would mean 5 times cheaper going down the bitumen route. This equates - lo and behold - to a period of 10 (ish) years too!!!

 

So after 10 years have passed - monetarily - not much in it.

 

However, if you owned a boat with a zinca hull - how often would you haul it out for inspection?  And now the additional costs of haul out/in come into play.

 

I think I liked the idea initially of the Zinca hull because of its superior properties compared to good old tar (bitumen). Paint it on and forget it.  But it's not that simple is it?  Curiosity would persuade me to haul the boat out every 2-3 years anyway to get that comfy feeling that nothing sinister is ongoing under the surface.

 

Views?

We paid circa £600 to get our 60 footer blacked in 2017. I was thinking that maybe the full coast of a 2 pack epoxy would be £3000 ish. I'd never try and paint myself. Got fed up with that antifouling our lumpy water boat. Looks like zinga would add another grand from Peters numbers to that by the time the yard has put their markup on.

Much cheaper doing it yourself but the chance of coating failure increases if you are new to these type of coatings and don't understand dew points.

Maybe someone who has used epoxy can put some real prices in for grit blasting.

Edited March 1, 2019 by Dr Bob

[Sea Dog]

32 minutes ago, Dr Bob said:

Much cheaper doing it yourself but the chance of coating failure increases if you are new to these type of coatings and don't understand dew points.

Bob, I still struggle to come to grips with the idea that all of these "better" coatings require prep standards so hard to achieve that a Boater can't manage it (dew point problems aside, but they're avoidable).  Surely out in the real world, between tides or whatever, there's protective coatings being slapped onto metal structures in a short time window that would stick well to a narrowboat that's had a good high pressure wash (which appears to be able to remove blacking relatively well) and a dose of mechanical sander.  Yes, grit blast gives the perfect surface prep, but that can't be achievable in some of the fields where these coatings are having to be used, can it? Is there really not  a surface tolerant 2 pack (or whatever) that the competent boat blacker could apply successfully?

[Dr Bob]

31 minutes ago, Sea Dog said:

 Is there really not  a surface tolerant 2 pack (or whatever) that the competent boat blacker could apply successfully?

Not that will last for more than a couple of years.

I was involved in the 80s in trying to find a better splash zone coating for offshore platforms (when working in BP). That's what got me into coatings.

Typically they will grit blast to get the surface clean over a week or so. Then on the day of painting, they would re-grit blast to remove rust bloom and moisture and get a first coat of coal tar epoxy on asap before the rust bloom came back. Coal tar epoxy is slightly more forgiving than 'normal' epoxy.

Any attempt to get a 'tolerant' coating always failed as nothing really made it any better. All tolerant coatings were a compromise. We did however get somewhere down the road by putting something in to the formulation that mopped up oil, so we had an oil tolerant coating. It really worked but was still a compromise. It doubled the life of coatings used in the paper industry (on paper machines) where surface preparation was almost zero. We got 2 years performance rather than 1. Problem was that the coating was very expensive so instead of normal paint job requiring £1000 of paint and £9000 of surface preparation, we were aiming at a market of £4,000 for the coating and £4000 for the preparation. You can imaging the painting contractors didnt like this and fought very hard to discredit the coating. It did manage to get a niche market but only in very difficult to apply areas. It would however have worked well for NB and likely have given results as good as the 2 pack epoxies today. A big problem however was shelf life and that was less than a year.....no good for NBs then!

I doubt if the paint manufacturers will ever get a 'tolerant' coating as the steel paint market is dominated by the painting contractors (who use much much more coating than we do) and they want to continue to blast to SA2.5 to make money. They dont want any of 'their' part of the pie going to the paint manufacturers. There is therefore a big commercial driver not to develop tolerant coatings. Obviously if one did appear, it would make loads and loads of money but unfortunately the chemistry to succeed is very difficult and no one has found it yet. Our coating from the 80's did work, but would have been 5 times the price of conventional epoxies - and it was very difficult to prove it was better. The only test is really 10 years in the market place - and new coatings dont get that opportunity.

I dont think much has changed in 30 years other than certain components being taken out (which makes the current offerings worse) or moving to water based (which makes the current offerings worse). If anyone does come up with a new 'revoloutionary' tolerant coating then I would be very sceptical and only be convinced after years of very positive responses from the users. The chemistry of coatings has not changed in 30 years. All tolerant coatings are a compromise but may give 2-5 performance. Traditional blacking is a good example of that.

[Sea Dog]

4 hours ago, Dr Bob said:

not that will last for more than a couple of years.

I was involved in...

Thanks for the comprehensive explanation. 

 

[TGweeder]

Just read through this thread.

I have over the past few days been talking to Zinga UK.

I have a 50ft narrow boat to paint.

Worked out it's about 67 m2 including the base.

Price for the Zinga 2 x 25kg £800

Price for the pu tarfree M10 (Zinga recommend) for blacking over going for 3 x 4lt tins £323 

 

Hopefully I have attached some screenshots of a case study they did and the tarfree pdf.

 

I am doing all the prep grit blasting ect myself so only have to buy the goods.

 

Hope it's of interest.

 

Zingatarfree_TDS.pdf

[cuthound]

If I recall correctly @peterboat of this parish used Zinga blacking over Zinga, but found that it faded quickly to a grey colour. Since then he has covered the Zinga blacking with Keelblack with satisfactory results.