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cobbett
cobbett

Posted: Sat May 12, 2012 8:31am

Post Subject: Hull preparation and treatment.

Hi, I have a 60 ft widebeam narrowboat in France. I need to lift her out and work on her hull. As I have not done this before I would appreciate any advice /recommendations. The hull has some rust that will need to be removed. So I am assuming that I should power wash the hull, then wire brush the rust areas back to bare metal. I would then like to apply as long a protective coat as possible, as lifting out a 24 tonne boat in France is difficult and expensive. Are there special 2 pack applications ? or special bitumous compounds I could apply. Also, do I need to do the flat bottom of the boat ? One last question, if the boat is showing signs of rust, how quickly do I need to do the work ? I think the bottom plate is 10mm. Thanks, David.

Tony-B
Tony-B

Posted: Sat May 12, 2012 10:48am

Post Subject: Hull preparation and treatment.

The hull sides may only be 6mm thick so those are the things to worry about. The question about coating the bottom plate is constantly under discussion but if you rarely ground the boat it would probably be better to coat it than not. Especially if using a product that is tougher than normal blacking. Ordinary blacking is either based on tar or bitumen and in the main you have to stick with what is on there because you can get a reaction so the new stuff falls off. If you clean a patch and the rub it with a rag soaked in white spirit or diesel then if the blacking softens and rubs off on the rag it is bitumen. You should not use any form of primer unless it is specifically designed for going under blacking. You can get two pack blackings which are supposed to be far longer lasting but originally they needed a hull sand blasting clean, I think there is now a wet blasting process that makes marginally less mess. I understand there is now at least one two pack product that does not demand the hull be blasted clean (we are NOT talking about a pressure wash when I say blasting). Blakes (now Hemple) published a leaflet about blacking a steel boat and said that a wire brush polishes the steel and makes it harder for the coating to stick so they advised a final run over with a disk sander. International make Primocon which is an underwater primer and some yards put that under blacking. Whatever is used it is vital to really scrub the coating into all the rust pits. With conventional coatings often the first coat is thinned or a thinned product is used. Apart from the two pack products the blackings (both types) are available in different formulations with the more expensive giving greater protection from a variety of hazards. I suggest that you spend some time Googling because you could end up paying a lot of money for a process and coating that might not be cost effective. Some makers to look at: International, Hemple, Mainline Building Products, and probably more. Tony Brooks

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