Keel varnishing - where is my fault?

[branko]

Every year when I prepare boat for season I must completely remove old paint from my steel keel and put new one. This year I put Hempel primer than 2 coats Hempel light primer and antifouling. During last few days I made a checking and find out that on upper part of keel exist a lot of bubbles Now I am sure that next year I must remove all varnishing to metal again.It makes me crazy!
Does anybody have solution?

 

[Evadne]

I think you may have some rust between the paint and the metal.

I too have a (cast) iron keel. It is about as smooth as the surface of the moon, and to be honest I don't even try to get it smooth and fair, but if you really want to, for instance to gain that extra 1/2 knot when racing:
1) shot blast so that all rust is removed
2) prime, immediately. Rust will start to form and after more than an hour even the primer may not stick properly.
3) then fair (epoxy, car filler or whatever you choose)
4) antifoul.

 

[Gordonmc]

Most primers are, in fact, porous and rely on a topcoat to act as a moisture barrier.The primer is there to help the topcoat stick to the substrate.
I think the answer is to get the steel as clean of rust as possible, prime and then use an epoxy tar before antifoul.

 

[Topcat47]

Don't use car stuff it's hydroscopic. In cars it's the paint system that keeps the water out, not something you can rely on anti-foul to do.

 

[simonfraser]

i seem to remember a post on this, blast it, wait for a thin layer of rust, then put rust converter on, then paint, job done

 

[Guest]

Car stuff .........

Bopll%oks

What a load of ,,,,,,,,,,

 

[simonfraser]

hmm,

search under Neutrarust and u shall see

 

[Topcat47]

Re: Car stuff .........

You wanna pay for the repaint on my boat after some joker used it under the deck paint?

 

[GMac]

Re: Car stuff .........

On our steel barges we used some 2 pot primer stuff, Joten (err.. spelling issue possibly) not Hempel, that says we get clean metal then wash with water and wait for hint of surface rust (around 12-24 hours) then apply. It won't work as well onto fresh clean steel. Then another primer and anti-foul.

It is magnificent and I would not consider changing ever.

Maybe have a close read of the instructions and see if yours needed the same.

One of the other guys had a similar sounding problem which turned out to be an electrical issue.

 

[Guest]

Painting steel / iron etc.

Blasting of metal produces a surface that is pitted and also too clean for painting .... the actual spec for metal ready for painting is :

SA1.5 ..... which equates to dull grey.

Some products will actually advise to leave the surface a short period to allow the corrossion to restart ... I am not a paint chemist and cannot advise why ... but this is supposed to aid bonding.
You can see easily if you try to paint clean shiny metal - the cover is terrible and the paint just wont give even coat, it tends to streak ....

IMHO .... I would go for a two pack system based on epoxy .... giving superior adhesion and barrier strength.

To Topcat47 ... I apologise for my previous post .... that's the problem with having a few beers then posting !! But car paint hygroscopic ?? Ok it used to be that cars were painted with cellulose based paint which has an apprecaition of water in uncured state .... but one the solvent is evaporated out - that stops. Second paint does not stop moisture getting through ... it's the number of coats that does it. Primers are notoriously lacking in barrier protection, relying on successive coats and top-coat to provide it. Anyone using car paint on a boat is really being too cheap or wasting their time / money. It doesn't have the body or strength required. The first mention of car material actually though was as filler - not as paint ...

 

[branko]

Re: Painting steel / iron etc.

Thanks a lot to everybody. I shell leave metal surface to obtain first light corrosion before first primer next time. Special thanks to Nigel - I see your text very well now and you can proceede with beers!

 

[oldharry]

[ QUOTE ]
i seem to remember a post on this, blast it, wait for a thin layer of rust, then put rust converter on, then paint, job done

[/ QUOTE ]

Go to all the trouble of removing the rust, then allow it to go rusty again!!!!

sounds /forums/images/graemlins/crazy.gif to me....

Rust convertor is for when you cant get the old rust off for some reason, like a heavily pitted surface. They are pretty gimicky anyway, and dont really belong outside the auto trade (or IN it many would say!)