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Posted: Fri Aug 28, 2015 5:43pm

Post Subject: Narrowboat Blacking

Hi folks, Any tips on blacking? Should I apply the bitumen paint directly to the steel or would you recommend applying a primer first/ red oxide?


Posted: Fri Aug 28, 2015 6:45pm

Post Subject: Narrowboat Blacking

First of all make sure it is coated with bitumen. Tar based blacking tend not to wash off in diesel polluted water. Soak a rag in white spirit and rub the existing blacking. If the blacking softens and comes off on the rag its bitumen. If it stays on the boat it is tar based so re-black with a similar product. You should not overcoat tar with bitumen or bitumen with tar. Hemple advise not to use a wire brush to remove rust because it might affect the adhesion of the blacking (of whichever type). They say finish with a grinding disk. It has been stated that red oxide reduces the blacking's adhesion but I do not know if it is true. International make an underwater primer (Primacon or some such name) that should be OK to use under blacking but I am sure at least half of boats have no primer. The maker of the blacking you choose should be able to advise further. Make sure you really scrub the first coat into all the rust pits, a roller is normally OK for further coats. Some people either use a thinner compatible product for the first coat or thin the blacking to get better pit penetration.

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