Two pack blacking - what to buy for reblacking over unknown product

[Odana]

We are booked into dock in a few weeks time to reblack the boat. We have two-pack on, but unknown brand - the previous owners couldn't remember other than 'it was from some industrial unit north of Burton'.

 

There are lots of scuffs and a few bare patches from use over 3-4 years, but not enough to warrant taking it back to steel all over. I understand from various searches that we can take back the worst bits to steel and then abrade all the rest that is still sound, and paint over everything. Two pack is a new thing to me so...

• What brand is recommended for putting over unknown two-pack, to get best 'stick' and value for money, (not super-cheap-but-crap or toppest-quality-but-eyewateringly-expensive - just want it to do the job)
• What's the approx realistic coverage rate so I can calculate how much to order for a 68ft boat
• Anywhere in particular that is best to buy? (we're in Brum and booked out at Hawne Basin)

Any other guidance on this job of touching up/repainting two-pack much appreciated!

 

 

[Sabcat]

I'm not sure what you can put over unknown 2 pack but the stuff itself isn't expensive. 5 litres of Dacrylate is about £50 which is enough for one coat on a 62ft boat. You want at least 2 coats.

 

The money is in the initial blasting of the hull. I think the primer is expensive as well but I'm told not all yards bother with it which if true is shonky in the extreme.

[nicknorman]

I think the primer is expensive as well but I'm told not all yards bother with it which if true is shonky in the extreme.

Not necessarily. Our boat has Sigmacover 300 which is designed to go straight onto the (blasted) steel without primer. It is self -priming and after 3 years ours is still perfectly bonded (except where we have scraped it off!). Some other coating are designed to be applied over primer, it just depends.

Edited April 15, 2015 by nicknorman

[Sabcat]

Not necessarily. Our boat has Sigmacover 300 which is designed to go straight onto the (blasted) steel without primer. It is self -priming and after 3 years ours is still perfectly bonded (except where we have scraped it off!). Some other coating are designed to be applied over primer, it just depends.

 

That's "proper" then, I was told a story about a yard (and I won't say who because it might not actually be true) that uses Dacrlylate and didn't even know a primer existed for it.

 

Also, the same yard apparently put the boats back in the water as soon as they're touch dry rather than giving them 5 days to cure.

[nicknorman]

 

Also, the same yard apparently put the boats back in the water as soon as they're touch dry rather than giving them 5 days to cure.

Dacrylate is a make rather than a specific product so it's difficult to check as I'm not familiar with the relevant product, but for Sigmacover 300 you can put it back in the water after 30 hrs at 15 deg. Of course it won't have its full abrasion resistance for a while, but since it cures by chemical reaction rather than evaporation it makes no difference whether it is in the water or not. It is a whole different concept from ordinary blacking.

[Midnight]

I would use Hempel Hempadur 15130 Coal Tar Epoxy

 

I used this when the two pack blacking I used previously was no longer available. Either sand or use a wire wheel to scuff up the existing coating. A word of warning use a gas filter in your face mask and only in a open sided dry dock. I once used two pack in a covered dry dock, the fumes were unbearable and I had a sore throat for days after.

Edited to add

Some companies won't supply to retail customers. A long way from you but Carters Paints in Sunderland usually have it in stock and offer trade prices to all.
I think two 5 litre tins will be enough to give you 2 coats on a 68ft boat - use a hairy roller. Three tins to be safe or a third coat.

 

I tried the equivalent product from Sigma but wasn't impressed

Edited April 15, 2015 by Midnight

[Paul C]

 

That's "proper" then, I was told a story about a yard (and I won't say who because it might not actually be true) that uses Dacrlylate and didn't even know a primer existed for it.

 

Also, the same yard apparently put the boats back in the water as soon as they're touch dry rather than giving them 5 days to cure.

 

Some 2 packs don't need a primer, are fine with a single coat applied, and can be applied to damp metalwork and reimmersed very soon afterwards and will cure underwater eg are suitable for tidal jetties etc.

[Old Son]

Mine is coated with Jotun. I have just had a quotation for paint to re-black and it is about £450!

[Odana]

Thanks all. So far we have suggestions to investigate of Hempel Hempadur 15130 Coal Tar Epoxy, Sigmacover 300 (though will it go over other stuff?), Dacrylate summat.

 

 

Has anyone else applied new two-pack over the old? Is there anything else I need to know apart from scuff it up very well first.

We are in an open dock up on a trolley, so luckily fume issues should be less than in a dry dock.

[system 4-50]

I used Jotamastic 87 over my builder's original and unknown 2 pack blacking last year. I will be able to tell you if it worked in about 4 years time.

[nicknorman]

Thanks all. So far we have suggestions to investigate of Hempel Hempadur 15130 Coal Tar Epoxy, Sigmacover 300 (though will it go over other stuff?), Dacrylate summat.

 

 

Has anyone else applied new two-pack over the old? Is there anything else I need to know apart from scuff it up very well first.

We are in an open dock up on a trolley, so luckily fume issues should be less than in a dry dock.

 

I know we haven't really answered your question, but the Sigmacover and Hempel at least, are both coal tar epoxy. Coal tar is coal tar and epoxy is pretty stable and unreactive once cured so I wouldn't envisage any issues putting one on top of the other. I haven't tried it though.

[NB Watersnail]

We've had unknown epoxy on our hull when purchased. We were advised that epoxy over epoxy wasn't the best idea as the existing blacking was unlikely to provide a good key for the new.the advise was (I forget who advised this) to overcoat with Intertuf 16, a single pack blacking. I've done this several times now with faultless results. When we were lengthened the new steel was blasted and epoxy primed at the mill. We applied dacrylate 2 pack to this, let it cure and then Intertuf over the top, as the Intertuf has a very different finish to 2 pack. Been back in now for over a year and all is still well.

[Odana]

We've had unknown epoxy on our hull when purchased. We were advised that epoxy over epoxy wasn't the best idea as the existing blacking was unlikely to provide a good key for the new.the advise was (I forget who advised this) to overcoat with Intertuf 16, a single pack blacking. I've done this several times now with faultless results. When we were lengthened the new steel was blasted and epoxy primed at the mill. We applied dacrylate 2 pack to this, let it cure and then Intertuf over the top, as the Intertuf has a very different finish to 2 pack. Been back in now for over a year and all is still well.

This is the dilemma. If we go for a 'normal' blacking that's it forever and we can't then go back to two pack without blasting the lot back to steel. Ideally I'd like to stick w two-pack - what do others do when their two-pack needs touching up after a few years?

[David Mack]

This is the dilemma. If we go for a 'normal' blacking that's it forever and we can't then go back to two pack without blasting the lot back to steel. Ideally I'd like to stick w two-pack - what do others do when their two-pack needs touching up after a few years?

 

I seem to recall that in the Narrowboat Builders Book Graham Booth reports that sections that had been damaged were taken back to bare metal with full 2-3 coats of epoxy, but the rest was just cleaned off and given a single coat for cosmetic reasons.

[nicknorman]

This is the dilemma. If we go for a 'normal' blacking that's it forever and we can't then go back to two pack without blasting the lot back to steel. Ideally I'd like to stick w two-pack - what do others do when their two-pack needs touching up after a few years?

In the Sigmacover instructions, for over-coating it just says to abrade the surface and then apply more 2-pack. I would just apply the 2-pack having given it a good whizzing with something (rotary wire brush maybe, if it's no too hard) and de rusting any bare bits. As you say, if you put 1-pack on there is no going back the other way, and I think if you are used to 2-pack you would be disappointed how poorly it lasts.

[b0atman]

2 pack means what ?

[Paul C]

2 pack means what ?

 

2 part paint - the 2nd part being a hardener, which is mixed with the paint just before it is applied. Basically, it hardens via a chemical reaction process rather than evaporation like normal paints, which results in a much stronger paint.

Edited April 25, 2015 by Paul C

[Timleech]

I've used Epicol CT (from Spencer Coatings/Mainline) over unknown existing 2-pack, seems to be fine, at the time it was more economically priced than a lot of the competition.

Epimastic WT, from the same people, might be a better bet in some situations.

 

Tim

[Traveller]

I have never heard before that two pac cannot be over-painted with two pac. Certainly our old broads cruiser was painted in two-pac on the top-sides and we had no problems overpainting that with more two-pac.

[Odana]

Sigmacover on order. We'll see how it goes but am confident all will be good - thanks for the advice, all