Blacking or epoxy coating?

[Sea Dog]

^^^^ That sounds like the way forward to me - let the yard and the paint manufacturer sort the responsibility, because its hard to see how the customer could be at fault!

[Lizzy]

It was Hempadur 45143. While I was at the boatyard they did confer with the Hempel rep. Because of delays due to bad weather it had only been three days of curing by the planned date to be put back in. Hempel advised that that's not long enough at this temperature and advised another day. Because of logistics at the boatyard I staid 3 days longer.

Thank you so so much for your help. I am waiting for another response from Hempel as I had replied to them with all the details. Then will write an email to them both. Fingers crossed.

[WotEver]

Good luck

 

[blackrose]

This is the problem of expecting canal boatyards (most of whom are used to pressure washing and just slapping a couple of coats of bitumen onto a boat), to do a decent job with a more technical epoxy paint system. Steel prep, paint mixing, overcoating times and final cure times before reimmersion are all important factors and personally I wouldn't trust many yards to do the job properly.

 

I got my boat grit blasted and did the painting myself. I applied 2 coats of jotamastic 87 with aluminum, followed by 2 coats of jotamastic 87 black. I made the mistake of using standard grade hardener because I be was mixing whole 4.7 litre cans and thought I wouldn't get winter grade on within the pot life, but I probably could have done. Standard grade takes longer to cure and the temperature that summer wasn't particularly hot so I ended up booking the dry dock for an extra week to make sure it was fully cured before going back in the water. It's rock hard.

Edited October 6, 2018 by blackrose

[Dr Bob]

1 hour ago, blackrose said:

This is the problem of expecting canal boatyards (most of whom are used to pressure washing and just slapping a couple of coats of bitumen onto a boat), to do a decent job with a more technical epoxy paint system. Steel prep, paint mixing, overcoating times and final cure times before reimmersion are all important factors and personally I wouldn't trust many yards to do the job properly.

 

There are certainly a lot of things that can go wrong with 2 pack epoxies.

1 hour ago, blackrose said:

 

I got my boat grit blasted and did the painting myself. I applied 2 coats of jotamastic 87 with aluminum, followed by 2 coats of jotamastic 87 black. I made the mistake of using standard grade hardener because I be was mixing whole 4.7 litre cans and thought I wouldn't get winter grade on within the pot life, but I probably could have done. Standard grade takes longer to cure and the temperature that summer wasn't particularly hot so I ended up booking the dry dock for an extra week to make sure it was fully cured before going back in the water. It's rock hard.

My personal view is that using standard grade hardener gives a higher cross link density...so harder cure than a winter grade as long as temps are over 15°C for a good part of the time. Winter grade hardner 'forces' the reaction and my view over a large number of years working with polyesters and epoxies is that it doesnt achieve that full cross link density. Other experts may disagree. I dont like the idea of accelerated hardener to paint between 10 and 15°C as you are far more likely to be painting near the dew point so moisture contamination. No. Epoxy coatings are best applied at 'summer' temperatures.

I'm not sure though that Lizzy's problem is temperature of cure. Its been warm down here in the south over the last 2 weeks. The weather was pretty awful the week she had the boat painted....it was that very windy week I seem to remember and not too warm. We also dont know how they did the painting. Was it in a shed etc?

[rusty69]

I used some jotamastic 87 primer in our engine room last year (with helpful guidance from mr blackrose).I think I used the winter hardener,even though it was summer due to the surface temp of the steel  being cold due to contact with the canal water.

 

Obviously not as critical as a good cure on the underwater external hull parts as in Lizzies case. It would be interesting to know which grade hardner the boatyard in question used.

[blackrose]

7 minutes ago, Dr Bob said:

There are certainly a lot of things that can go wrong with 2 pack epoxies.

My personal view is that using standard grade hardener gives a higher cross link density...so harder cure than a winter grade as long as temps are over 15°C for a good part of the time. Winter grade hardner 'forces' the reaction and my view over a large number of years working with polyesters and epoxies is that it doesnt achieve that full cross link density. Other experts may disagree. I dont like the idea of accelerated hardener to paint between 10 and 15°C as you are far more likely to be painting near the dew point so moisture contamination. No. Epoxy coatings are best applied at 'summer' temperatures.

 

 

I've often wondered whether winter grade hardeners will produce the same final coating performance as standard grade. Like you I always suspected there must be some trade-off using winter grade, but my thoughts were only intuitive rather than based on any technical knowledge. According to Jotun there's no disadvantage in using winter grade, but I suppose they would say that.

 

This summer I took my rusty stern deck back to metal and painted it with a combination of jotamastic 87 with standard and winter grade hardeners applied in high temperatures. I haven't got around to the undercoats and deck paint yet, but it seems ok, very hard. I hope it's ok but time will tell.

 

[blackrose]

11 minutes ago, rusty69 said:

I used some jotamastic 87 primer in our engine room last year (with helpful guidance from mr blackrose).I think I used the winter hardener,even though it was summer due to the surface temp of the steel  being cold due to contact with the canal water.

 

 

We did the same thing using Jotamastic 87 and WG hardener when we repainted the bilges of Streatley and Nuneham, Thames steam boats, while they were in the water. Even in summer the steel is quite cold. That was under instruction from the technical paint manager from the Cutty Sark project who came to visit us.

[Lizzy]

It was done outside and yes in the first two weeks both the gritblasting and the epoxy spraying were postponed on some days due to bad weather. It was very windy in the week that the two epoxy coats went on. They covered the sides in plastic sheeting but not the roof. I had tiny sprinkles of epoxy all over the roof. 

 

The boatyard is the only one in the area doing the gritblasting and it is booked ahead for months. There were boats waiting to be gritblasted when I left. I can only assume that they know what they are doing (generally). Everything done there looked very professional. I was not on site though to see the application on my boat. I have no reason to doubt their competence. Yet here I am with this substandard coating ?

[Sea Dog]

2 hours ago, Lizzy said:

 I have no reason to doubt their competence. Yet here I am with this substandard coating

I'd say you have at least some reason to have at least a little bit of doubt! Sounds like they were struggling with the conditions but, whilst you as the customer might then have to accept a delay, you shouldn't have accept a sub standard result. I expect that they wouldn't want you to either and there'll be a satisfactory outcome.  Even the best can make rare mistakes - its how they deal with them that the true measure.

[WotEver]

27 minutes ago, Sea Dog said:

Even the best can make rare mistakes - its how they deal with them that the true measure.

Nicely put

 

[Lizzy]

30 minutes ago, Sea Dog said:

I'd say you have at least some reason to have at least a little bit of doubt! Sounds like they were struggling with the conditions but, whilst you as the customer might then have to accept a delay, you shouldn't have accept a sub standard result. I expect that they wouldn't want you to either and there'll be a satisfactory outcome.  Even the best can make rare mistakes - its how they deal with them that the true measure.

That is very true. As they have been so good and accommodating while I was there I am hopeful too that this will be resolved. I have written to the boatyard and manufacturer together yesterday asking for somebody to come out and do a personal diagnosis. Boatyard has always been immediatly responsive before. Not this time which makes me think that they are considering. 

[Tim Lewis]

On ‎05‎/‎10‎/‎2018 at 16:29, yabasayo said:

If we end up with a decent narrowboat following our move from sea going yachts, I'll definite look at getting the hull hot zinc sprayed, effectively galvanised. With a coat of paint on top supposed to last indefinitely. No idea about the cost though.

http://www.debdalewharf.co.uk/hull-protection-prices/

 

[blackrose]

On 05/10/2018 at 16:29, yabasayo said:

If we end up with a decent narrowboat following our move from sea going yachts, I'll definite look at getting the hull hot zinc sprayed, effectively galvanised. With a coat of paint on top supposed to last indefinitely. No idea about the cost though.

 

Is it really effectively galvanised? I thought galvanizing metal involved introducing electrical charges to create positive and negative ions which were attracted to each other. Is that the case with hot zinc spraying?

[Tim Lewis]

52 minutes ago, blackrose said:

 

Is it really effectively galvanised? I thought galvanizing metal involved introducing electrical charges to create positive and negative ions which were attracted to each other. Is that the case with hot zinc spraying?

 

Some info

 

http://www.debdalewharf.co.uk/zinc-metal-spraying/

 

[Dr Bob]

4 hours ago, Lizzy said:

That is very true. As they have been so good and accommodating while I was there I am hopeful too that this will be resolved. I have written to the boatyard and manufacturer together yesterday asking for somebody to come out and do a personal diagnosis. Boatyard has always been immediatly responsive before. Not this time which makes me think that they are considering. 

Lizzy, look out for a pm from me. I can help you with some testing that should encourage Hempel to sort this out.

Too much detail for the forum!?

[Captain Pegg]

1 hour ago, blackrose said:

 

Is it really effectively galvanised? I thought galvanizing metal involved introducing electrical charges to create positive and negative ions which were attracted to each other. Is that the case with hot zinc spraying?

It depends how you define galvanising. In lay terms it might wash since the method by which the zinc protects the steel is still galvanic but in technical terms it is not equivalent to hot dip galvanising.

 

Hot dip galvanising produces a chemical bond between the zinc and the oxidised surface layer on the metal and therefore has very strong adherence between the coating and the parent metal. Hot zinc spraying only produces a mechanical bond so the adherence between coating and parent metal is less strong. It also means the process is subject to similar requirements and risks as apply to two pack epoxy in terms of preparation of the surface. 

 

The finished coating is porous so it needs to be sealed, although I have seen one company claim this is advantageous as it allows the steel to "breathe". I wouldn't be using them if I wanted it done.

 

JP

Edited October 6, 2018 by Captain Pegg

[Bee]

I used Jotun 87 on my boat this spring, All seems OK, Some of the paint with no hardener added to it found its way onto the handles of a couple of scrapers - its still sticky. It needs a really good stir to mix it properly.

[yabasayo]

12 hours ago, blackrose said:

 

Is it really effectively galvanised? I thought galvanizing metal involved introducing electrical charges to create positive and negative ions which were attracted to each other. Is that the case with hot zinc spraying?

Looks like you may be confusing galvanic cells, where one metal corrodes preferentially when two different types of metal are in contact with each other in an electrolyte, with galvanising, which is coating a metal, usually steel, with zinc. Normally the steel component is immersed in molten zinc to coat it. In the case of large items where this is not possible, the molten zinc is sprayed onto the steel.