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Re-appearing rust under paint after Craftmaster recommended paint job just months ago


Tiboo

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So after a few failed quick paint jobs in July '21 I thought let's get this done properly and I meticulously followed the Craftmaster hints & tips, descaling rust patches thoroughly to bare metal (by hand + power sander), applying & rinsing Fertan, 2x primer, 2x undercoat and 2x top coat (only the top coat was 'International' paint, to preserve the color). Only 4 months later, I noticed little bubbles appearing in the paintwork in several locations. In the first place I'd like to know what went wrong.

(1) Would it be because of some rust particles that may have remained even after the thorough descaling? (Can rust grow even with all this paint on top of it?)

(2) Would there still have been water particles on the metal after the (recommended) Fertan rinse-off? (Though, I wiped it dry and gave it about half an hour further drying time).

(3) Would it be due to the occasional rain that appeared after I had applied the undercoats?

(4) Something else?

I wonder if I would be better off applying a few epoxy coats + top coat. I haven't got any issues on my hull where I followed this approach (and I had some corrosion around the waterline)... Yet, I'd be very curious about the cause before I re-invest my time and money...

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I think the fertan is your issue…I’ve never had any success with it…I much prefer Vactan and it doesn’t need rinsing which just seems wrong to me to introduce water onto a surface you don’t want moisture in. I suspect unless you dried the surface with a hot air gun there was trapped moisture.  

  • Greenie 2
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I would also question the Fertan. If you have got absolutely back to bare metal then there is no need for a rust treatment, in fact I believe it will do harm, with Fertan you will be putting water onto bare steel, and Vactan is designed to bond to rust, not to bare steel. The concept of using rust treatment on bare steel "just in case" is a new and badly thought out fad. Just go direct to a good quality zinc primer. The rain on the undercoat might also be a problem, especially if you put top coats on before the undercoat was 100% free of water.

International on top of Craftmaster should be fine.

What a bummer.

 

did you get back to 100% bare metal or did you possibly have a bit of rust at the bottom of any pits?  Pits could easily hold a bit of rinsing water.

  • Greenie 3
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Fertan and Vactan are rust converters.  So if you have gone back to clean steel (not just wire brush-polished rust) then there is nothing to convert.  So when you rinsed off the Fertan you will (should) have rinsed off everything and gone back to bare metal. So not only was the time and money spent on Fertan wasted, but in washing it off you have wetted the bare steel, which will have allowed it to start rusting again. Best thing would have been to have got a decent primer onto the bare steel as soon as it had been cleaned. 

 

Vactan does not need the excess washing off, but dries to an acrylic(?) coating which acts as a primer. Some say this is fine, others argue that a water-based acrylic coat is not a sensible foundation for a later oil-based paint system.

Edited by David Mack
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Interesting, thanks!

 

I only painted top coat much after the rain so that shouldn't be the issue I guess.

There was some pitting here and there, and I could indeed not always reach those areas so well for descaling, I should have mentioned that. I'm just not sure how to deal with this, would a needle-gun be a must there..?

 

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16 minutes ago, David Mack said:

Fertan and Vactan are rust converters.  So if you have gone back to clean steel (not just wire brush-polished rust) then there is nothing to convert.  So when you rinsed off the Fertan you will (should) have rinsed off everything and gone back to bare metal. So not only was the time and money spent on Fertan wasted, but in washing it off you have wetted the bare steel, which will have allowed it to start rusting again. Best thing would have been to have got a decent primer onto the bare steel as soon as it had been cleaned. 

 

Vactan does not need the excess washing off, but dries to an acrylic(?) coating which acts as a primer. Some say this is fine, others argue that a water-based acrylic coat is not a sensible foundation for a later oil-based paint system.

I think Vactan dries to an vinyl primer.

 

I use it on steel, rusty it converts. bare it coats.  Then I use Bondaprimer, 2 coats.  Even left without a top coat it does not rust through. You have to leave the Bondaprimer several days to cure fully or you can get reactions with the next gloss coat.

  • Greenie 1
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I am no painter but from what I have picked up this sounds like micro-blistering and that seem to have three courses.

 

1. Solvent entrapment when you re-coat before the full thickness of the paint film has cured so that could be applying the new coat too soon or applying when excessively hot or sunny so the top of the paint dries before the bottom of that application film.

 

2. Damp trapped under the paint film so painting when it is too cold so you get condensation on the surface or not waiting for the morning sun to completely dry any overnight dew.

 

3,. Leaving something sitting on the paint that traps water against the  paint because paint is porous so water will eventually penetrate the film (not sure about two pack though).

 

Just from reading I get the impression this  might have been a bit of a rushed job because of time restraints. If you have actual rust then as primers tend not to be as waterproof as top coats then the rain could be the issue.

 

  • Greenie 3
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Could the bubbles be water trapped in the primer and undercoat? Both can absorb water which when over painted is trapped in, bit of heat and bubbles appear used to be common in car painting jobs 

Edited by peterboat
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Questions 1,2 &3.  Yes to all.

 

You will never remove all the rust once the surface has pitted, without either grinding metal away so all the pits are removed, having the surface abrasive blasted or by very high pressure water blasting (40 k psi, with inhibitor in the water). Rust conversion is important if you cannot do one of these because  rust itself contains it's own water to keep the rusting process going.

 

Then there are the painting conditions.  The surface of the steel needs to be at least 10 C above the local dew point temperature when any paint is applied, and until the paint has become touch dry.  That can be very hard to achieve, even in a dock.

Primer is usually porous, though I think Bondaprimer is one that is not. If it rains on primer, or even a heavy dew, it takes ages, in warm conditions,to get the primer itself properly dry. That encourages rusting particularly if there is minute traces of rust on the steel.  The pores in primer are part of the keying process, so dampness weakens the bond. Trapped damp also causes small blisters to appear. Google "microblistering in paint" for more information.

 

N

 

  • Greenie 2
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In my opinion if you must use a rust converter then Fertan is better than Vactan, I've had better results with it anyway. But it has to be used properly. As David says, if there was no rust to convert you may have just contaminated the bare steel. 

 

I disagree that you can't remove all the rust mechanically. It depends on the level of pitting of course but also how well you can prep steel. Lots of proper boat painters don't use rust converters.

 

But as others have said, the problem might be nothing to do with the converter or your steel prep. There are a whole host of environmental factors that can ruin a paint job, many of which are exacerbated by not doing the job undercover.

 

 

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B Engo should have 10 stars..every point is critical.........and for the record,rust converting liquids cannot penetrate pitting completely  ,unless you immerse the hull in a tank of hot liquid for several hours.........,high pressure waterblasting 40-60,000 psi ,does not create a profile ,so the steel must have been previously grit blasted....which new steel should be before coating.

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18 hours ago, BEngo said:

Questions 1,2 &3.  Yes to all.

 

You will never remove all the rust once the surface has pitted, without either grinding metal away so all the pits are removed, having the surface abrasive blasted or by very high pressure water blasting (40 k psi, with inhibitor in the water). Rust conversion is important if you cannot do one of these because  rust itself contains it's own water to keep the rusting process going.

 

Then there are the painting conditions.  The surface of the steel needs to be at least 10 C above the local dew point temperature when any paint is applied, and until the paint has become touch dry.  That can be very hard to achieve, even in a dock.

Primer is usually porous, though I think Bondaprimer is one that is not. If it rains on primer, or even a heavy dew, it takes ages, in warm conditions,to get the primer itself properly dry. That encourages rusting particularly if there is minute traces of rust on the steel.  The pores in primer are part of the keying process, so dampness weakens the bond. Trapped damp also causes small blisters to appear. Google "microblistering in paint" for more information.

 

N

 

All good, Bondaprimer is resin based not solvent so that's why it is not porous. I have used it for years. The only problem is the reactions with the next paint coat if you rush and don't allow time for it to cure fully.

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16 minutes ago, Tracy D'arth said:

All good, Bondaprimer is resin based not solvent so that's why it is not porous. I have used it for years. The only problem is the reactions with the next paint coat if you rush and don't allow time for it to cure fully.

 

Ive never had this problem, one of the big strengths of Bonda is that you can get two coats on and then the first undercoat in less than an hour on a warm day. Bonda will give big trouble if you put it on top of standard boat enamels unless they are 100% dry (several days)  and can also lift the edge of a sanded/feathered repair in enamels.

 

Bonda is waterproof but the rust will still come through if left exposed to rain for a few week. All paints are slightly porous and Bonda is very thin so the wet will eventually get through.

 

To the op....is the bubbling all over/random or is it at the places where you had pitting?

I find that if I take pitting to 99% bare steel (but accept that there is a little rust in the deeper pits) and use a couple of coats of Bonda (NO rust converter) then several coats of paint (Craftmaster undercoat) then there is usually no rust problem. I try to do the sanding, Bonda and first undercoat on a sunny day.

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I once painted a steel hatch (which was  under cover in the wheelhouse) with a clear laquer (which supposedly was OK for steel) over the next few years until I got fed up and stripped it off it was fascinating to watch the brown rust spread underneath it, at no time did it start to lift; if it had not been a clear laquer but a paint you would never have known that it was quietly  rusting under the surface.

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Thanks for all that feedback! Luckily I'm only asking now as if I'd have all those ideas before the job I may have never tried to go for it anyway ;~)

Luckily not all the spots have failed, and together with your feedback I think I'm starting to figure out what happened.

5 hours ago, dmr said:

To the op....is the bubbling all over/random or is it at the places where you had pitting?

 

That's a good question indeed. I'm noticing it's actually NOT on the pitting. I did apply some filler to the pitting though, so that explains, of course! However, the rust issue only appears on the sides and nowhere on the roof, which I painted in the same period but in a somewhat asynchronous timing. I checked some logs I made and noticed there has been some rain half a day after I had applied the Fertan on the sides, which I wiped up and I waited two more dry days before applying the primer. I guess that's where things went wrong!

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43 minutes ago, Njiruk said:

Thanks for all that feedback! Luckily I'm only asking now as if I'd have all those ideas before the job I may have never tried to go for it anyway ;~)

Luckily not all the spots have failed, and together with your feedback I think I'm starting to figure out what happened.

That's a good question indeed. I'm noticing it's actually NOT on the pitting. I did apply some filler to the pitting though, so that explains, of course! However, the rust issue only appears on the sides and nowhere on the roof, which I painted in the same period but in a somewhat asynchronous timing. I checked some logs I made and noticed there has been some rain half a day after I had applied the Fertan on the sides, which I wiped up and I waited two more dry days before applying the primer. I guess that's where things went wrong!

 

Did you do this painting during good hot weather with just the one shower, or was it during generally damp weather (not good hot sun) ???

Painting does appear to be a nightmare job with quite a few failures. Mine will need doing soon, I think I will hire a wet dock and pay a competent (and fast) painter to help me, but might still have the issue of damp weather. To date I have only done repairs to the cabin sides plus the entire roof, front and back, but because these are quicker jobs its easier to get a good weather window.

 

I have also used a fair bit of filler over pitting and holes in the existing paint, I go against conventional wisdom and put a couple of coats of Bonda Primer onto the bare steel then put the filler on top of this, and so far with 100% success.

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16 minutes ago, dmr said:

I have also used a fair bit of filler over pitting and holes in the existing paint, I go against conventional wisdom and put a couple of coats of Bonda Primer onto the bare steel then put the filler on top of this, and so far with 100% success.

 

I too put filler over anti-rust primer in areas where there is likely to be damage to the paint film. Polyester filler is even more porous than primer so the last thing I would want is damp filler sitting on bare steel. None ever fell off while I had the boat.

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1 hour ago, dmr said:

I go against conventional wisdom and put a couple of coats of Bonda Primer onto the bare steel then put the filler on top of this, and so far with 100% success.

But when you sand the filler you also sand through the primer, so you need to prime again.

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5 minutes ago, David Mack said:

But when you sand the filler you also sand through the primer, so you need to prime again.

I avoid sanding filler. Apply with a good flexible blade as smooooth as possible, paint with more Bondaprimer before gently taking off just the nibs.

 

Often I just keep adding primer until the pits are filled.

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39 minutes ago, David Mack said:

But when you sand the filler you also sand through the primer, so you need to prime again.

 

Sometimes I prime, fill, sand, bit more filler, more primer and repeat as required. I find its not easy to tell that the surface is adequately smooth till its got a layer of primer on it, so just repeat as required. That is where the fast drying of bonda is really useful.

 

If I get a single chip in a good area of paint I sand/grind it to bare steel then build up with filler, but if its an area of roof (for example) that is already "textured" I don't bother too much and just live with a bit more texture. Its not really viable or even desirable to have a perfect finish on a boat.

And I lower my standards a bit every year 😀

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