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Molten zinc and blacking


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Not my money!

It lasts for ten years.

So do you leave it ten years in the hope that their claim is true, or have it checked regularly (at additional cost) to be sure?

Cheap and cheerful and every two years seems good to me.

But each to their own.

Rog

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IT WORKS.

A very detailed process to ensure that your boat isn't rotting from the outside like more and more boats are due to increased galvanic corrosion. Debdale are long established and arent going to guarantee this process if they didnt think it was going to stand the test of time. 

I see boats coming in every two years with the same spots of orange blanketing their sides, black it and hope for the best(that nobody spills diesel in the cut near their boat). every two years those pits get ever deeper

blasting and two packing/comastic/zinga-ing etc gives so much more protection to hulls than the best bitumen blacking can. 

I havn't had Old Friends zingered as I have a Comastic coating - it went 8 years before a good recoat in 2014 and was added to again with a single coat in 2016. - no galvanic corrosion whatsoever. I would get her Zingered if it was just bitumen blacking.

 

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I've not looked at the technical details but epoxy blacking must be refering to 'Coal Tar Epoxy' which is a proven marine coating system used on oil rigs in the North Sea. It is basically a high performance 2 pack epoxy (the best material for a barrier coating over steel) blended with coal tar - a bitumen type material used in traditional blacking. The coal tar helps give a bit of flexibility to the inherently brittle epoxy. Coal tar epoxies have been the coatings of choice for splash zone coating offshore as they have a limited amount of tolerance to water contamination on a surface altough the normal surface preparation is to grit bals to SA.25 standard - ie pretty damn clean. Nothing is ever dry in the splash zone of an oil rig!.

I imagine these coatings are now being used in conjunction with zinc so that if there are defects or damage, the zinc will restrict further corrosion.

Good for narrowboats? Well yes, but expensive. If applied right ie surface grit blasted back to SA2.5 (old swedish standard) and coating applied at >15 deg C and at least 5 deg > dew point, and to the right thickness then that coating will last 10 years on the cut. Applied over zinc even better if there is a defect on the surface (a bit of oil or water) before spraying. ......BUT the big problem is that these coatings are still pretty brittle and with some people out there thinking Canals are a contact sport, there is bound to be siginificant damage which will cause cracks. These coatings work by stopping water and oxygen reaching the steel and so no corrosion. If cracks appear, due to damage, then water and O2 get in and corrosion will occur at that site. The zinc will help passivate but will it work for 10 years? I wonder if the warranty covers the intact coating but is invalid in an area where the boat has had a bang.

Coal tar epoxies will be expensive but the biggest cost is the blasting to get to pure steel and then applying the coating in adequate coating conditions - ie May-Sept. It is even worse when you start with a boat that is blacked. Not easy to get back to pure steel.

I used to be tech manager of a speciality coatings company - and we developed a novel coal tar epoxy contaning rubber - but that was ridiculously expensive!

I have just bought a 15 year old NB which needs blacking now. I'm just going to get the normal blacking done as I think there is too much potential to damage the coating hence the epoxy will not work as a barrier coating. Maybe the zinc will be the thing that makes this new coating work better. Maybe I will think about this product in 2 years time but I am not holding my breath.

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3 minutes ago, BoatyMacBoatface said:

Thanks for your replies. 

I'm torn - part of me says the boat is worth spending the money and part of me says how do I know it really works.

I guess I could follow Dr Bob and look again in two years...

If it helps our boat was done at debdale, zinc and two pack two years ago. Last month it was out of the water to change the prop and the surface still looked in mint condition. I know it is only two years in, but we do cruise 500/600 miles a year so we are happy with it.

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Copied from a post I wrote in May.

"My10 year old boat was treated with Zinga and 2 part blacking  from new.

The Zinga goes up to the rubbing strake and the 2 pack to the gunwales. 

Recently taken out of the water for inspection and advised that the blacking is still good for at least another 2 years.

Well worth doing it  my opinion."

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  • 3 years later...
On 14/06/2017 at 18:24, Phil. said:

If it helps our boat was done at debdale, zinc and two pack two years ago. Last month it was out of the water to change the prop and the surface still looked in mint condition. I know it is only two years in, but we do cruise 500/600 miles a year so we are happy with it.

Useful info, thank you. I wasn't filled with confidence by the person I spoke to on the phone, but have read on this forum that the guys doing the work are good. What was your experience with the work and the office/communication?

On 13/06/2017 at 23:29, Dr Bob said:

I've not looked at the technical details but epoxy blacking must be refering to 'Coal Tar Epoxy' which is a proven marine coating system used on oil rigs in the North Sea. It is basically a high performance 2 pack epoxy (the best material for a barrier coating over steel) blended with coal tar - a bitumen type material used in traditional blacking. The coal tar helps give a bit of flexibility to the inherently brittle epoxy. Coal tar epoxies have been the coatings of choice for splash zone coating offshore as they have a limited amount of tolerance to water contamination on a surface altough the normal surface preparation is to grit bals to SA.25 standard - ie pretty damn clean. Nothing is ever dry in the splash zone of an oil rig!.

I imagine these coatings are now being used in conjunction with zinc so that if there are defects or damage, the zinc will restrict further corrosion.

Good for narrowboats? Well yes, but expensive. If applied right ie surface grit blasted back to SA2.5 (old swedish standard) and coating applied at >15 deg C and at least 5 deg > dew point, and to the right thickness then that coating will last 10 years on the cut. Applied over zinc even better if there is a defect on the surface (a bit of oil or water) before spraying. ......BUT the big problem is that these coatings are still pretty brittle and with some people out there thinking Canals are a contact sport, there is bound to be siginificant damage which will cause cracks. These coatings work by stopping water and oxygen reaching the steel and so no corrosion. If cracks appear, due to damage, then water and O2 get in and corrosion will occur at that site. The zinc will help passivate but will it work for 10 years? I wonder if the warranty covers the intact coating but is invalid in an area where the boat has had a bang.

Coal tar epoxies will be expensive but the biggest cost is the blasting to get to pure steel and then applying the coating in adequate coating conditions - ie May-Sept. It is even worse when you start with a boat that is blacked. Not easy to get back to pure steel.

I used to be tech manager of a speciality coatings company - and we developed a novel coal tar epoxy contaning rubber - but that was ridiculously expensive!

I have just bought a 15 year old NB which needs blacking now. I'm just going to get the normal blacking done as I think there is too much potential to damage the coating hence the epoxy will not work as a barrier coating. Maybe the zinc will be the thing that makes this new coating work better. Maybe I will think about this product in 2 years time but I am not holding my breath.

Hi Dr Bob,

Did you go for zinc coating last year?

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10 minutes ago, 247 said:

Useful info, thank you. I wasn't filled with confidence by the person I spoke to on the phone, but have read on this forum that the guys doing the work are good. What was your experience with the work and the office/communication?

Hi Dr Bob,

Did you go for zinc coating last year?

There have been a few staff changes since we had it done, but we were happy with the entire process. The set up was very professional, and the end result excellent. We did not receive any paperwork regarding the guarantee, but had been previously warned that would be the case. Just to update you, our hull is still clear of any rust or wear at the water line a further two years on.

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12 minutes ago, 247 said:

Useful info, thank you. I wasn't filled with confidence by the person I spoke to on the phone, but have read on this forum that the guys doing the work are good. What was your experience with the work and the office/communication?

Hi Dr Bob,

Did you go for zinc coating last year?

No, I just went for the normal blacking. It seems to work well and control corrosion and I like the idea of taking the boat out of the water every couple of years. You may not do this if it were two packed.

The update is that we have just sold the boat and it's regime of normal blacking ( blacked in Aug 17 and May 19 ) has worked well with the sale survey showing no degradation in pitting etc. The survey from May 17 was almost identical to the new one in Mar 20.

We have bought a new boat and that has been blacked normally. Despite my knowledge of epoxy coatings, I think I'm happy to get the boat lifted every couple of years to check for problems. 

 

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10 hours ago, Dr Bob said:

No, I just went for the normal blacking. It seems to work well and control corrosion and I like the idea of taking the boat out of the water every couple of years. You may not do this if it were two packed.

The update is that we have just sold the boat and it's regime of normal blacking ( blacked in Aug 17 and May 19 ) has worked well with the sale survey showing no degradation in pitting etc. The survey from May 17 was almost identical to the new one in Mar 20.

We have bought a new boat and that has been blacked normally. Despite my knowledge of epoxy coatings, I think I'm happy to get the boat lifted every couple of years to check for problems. 

 

Thanks Dr Bob. I was happy with normal blacking for a decade but now have pitting. I did stop in a marina for a bit, with a galvanic isolator, so no idea if that had an effect or not. Imfortunately I'm on the next stage of the boating learning curve now, and leaning towards Debdale.

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16 hours ago, 247 said:

What was your experience with the work and the office/communication?

Mine was done on a hull March 2019 ( Boat first in the water August 2018-after sailaway fitout). About 5 months later noticed a blister about 50mm in size on the waterline below the shower outlet. Spoke to their office and they told me to return with the boat to sort out but not to worry as the coating underneath the blister would still be OK. Due to lockdown have yet to be able to get the boat back to them as it`s a 10 day oneway journey. Was expensive but their response to my issue was good. Will see what the hull is actually like when I can get the boat back to them.

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18 hours ago, Phil. said:

 Just to update you, our hull is still clear of any rust or wear at the water line a further two years on.

 

And that's the acid test. Contrary to what one contributor inferred on this thread back in 2017, you do not need to get your boat out of the water to check that any underwater paint system is working. Simply look along the waterline as that's the area that will be adversely affected first. My epoxy is still looking good along the waterline 5 years on with no signs of rust so I know it's still good.

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19 hours ago, Dr Bob said:

No, I just went for the normal blacking. It seems to work well and control corrosion and I like the idea of taking the boat out of the water every couple of years. You may not do this if it were two packed.

The update is that we have just sold the boat and it's regime of normal blacking ( blacked in Aug 17 and May 19 ) has worked well with the sale survey showing no degradation in pitting etc. The survey from May 17 was almost identical to the new one in Mar 20.

We have bought a new boat and that has been blacked normally. Despite my knowledge of epoxy coatings, I think I'm happy to get the boat lifted every couple of years to check for problems. 

 

I had mine zingered some years ago still no corrosion at the waterline as you know I keelblack for cosmetic reasons every couple of years but because of the virus looks like it going to be 3 years this time, I do the gunwales at the same time [rub them down and two coats of satin one pack polyurethane] I have the boat out in a drydock for 5 days which are long days getting all the jobs done

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3 minutes ago, cuthound said:

My boat was blacked with international 954  2 pack over Zinga when new.

 

Last year it had its first re-blacking (again with International 954) after 12 years of use.

Zinga works doesnt it? I shot blasted my front deck and zingered it, so \i have an idea what is going on underneath, looks great

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2 hours ago, blackrose said:

 

And that's the acid test. Contrary to what one contributor inferred on this thread back in 2017, you do not need to get your boat out of the water to check that any underwater paint system is working. Simply look along the waterline as that's the area that will be adversely affected first. My epoxy is still looking good along the waterline 5 years on with no signs of rust so I know it's still good.

We have been epoxied for a few years now and come out of the water every 3 or 4 years for epoxy repairs, but we are a hard working boat. Several scrapes happen above the waterline, mostly due to protruding lock collars, but otherwise any small local failures tend to be well below the waterline, the waterline is always good. I don't really understand this though mooring against sloping wash walls might be a factor.

 

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

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6 hours ago, jddevel said:

Mine was done on a hull March 2019 ( Boat first in the water August 2018-after sailaway fitout). About 5 months later noticed a blister about 50mm in size on the waterline below the shower outlet. Spoke to their office and they told me to return with the boat to sort out but not to worry as the coating underneath the blister would still be OK. Due to lockdown have yet to be able to get the boat back to them as it`s a 10 day oneway journey. Was expensive but their response to my issue was good. Will see what the hull is actually like when I can get the boat back to them.

I'd be interested to know the outcome when you do manage to get there. 

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17 minutes ago, TheBiscuits said:

 

It's where the tinworms chew through the paint to get at the steel ...

I was taught that tinworm only eat cars, especially those made by British Leyland, do you reckon they have evolved to eat boats too?

 

(I guess there are no BL cars left so they really had to evolve)

 

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

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11 hours ago, dmr said:

We have been epoxied for a few years now and come out of the water every 3 or 4 years for epoxy repairs, but we are a hard working boat. Several scrapes happen above the waterline, mostly due to protruding lock collars, but otherwise any small local failures tend to be well below the waterline, the waterline is always good. I don't really understand this though mooring against sloping wash walls might be a factor.

 

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

 

Yes I found the same with mine, any failures were from scraping against protruding bolts or towards the end of its life, the epoxy coming off on the stem post where it had caught the cill when locking up.

 

I hsve now repositioned the front fender a bit lower down, but may invest in a second lower front fender to protect against this.

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12 hours ago, dmr said:

I was taught that tinworm only eat cars, especially those made by British Leyland, do you reckon they have evolved to eat boats too?

 

(I guess there are no BL cars left so they really had to evolve)

 

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

Oh I dont know thay ate plenty of Fords, Vauxhalls and Datsuns ?

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