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richardg
richardg

Posted: Sat Mar 07, 2009 2:15pm

Post Subject: Hull Blacking

Tony I am about to have my hull blacked with bitumen but am unable to establish what is currently on (bitumen, comastic, or supertuff). Different people have looked at it and said different things and I don't want to strip back to bare metal. Please advise how you can tell for sure and does it matter anyway? Richard

Tony-B
Tony-B

Posted: Sat Mar 07, 2009 5:03pm

Post Subject: Hull Blacking

Dear Richard, The brand of blacking is unlikely to be as important as the base material. If we ignore two part epoxied blacking the choice is between tar based products and bitumen bases. It is said that bitumen based products can be used over tar bases but never the other way round, but I would not risk trying it without doing a test patch first and leaving it for awhile to see what happens. The usual way to test the blacking is to see if white spirit on a rag starts to dissolve the blacking. If it does than you probably have a bitumen based product, if not then it is probably tar based. I have done a web search for Supertuff but can not find any reference to it and I am not familiar with the name in respect of blacking, but there are a fair number of different products to choose from. Coamstic is tar based. To be honest, if you are paying to have it done for you you should not take it upon yourself to specify the actual product to be used. If you do and the job goes wrong it will be down to you. If you let your contractor recommend (preferably in writing) a list of suitable products and you choose from that list any problems should be down to him to put right. Tony Brooks

richardg
richardg

Posted: Wed Mar 11, 2009 7:03am

Post Subject: Hull Blacking

Tony sorry to sound numb but how do you do the white spirit test and what to look for? thanks Richard

Tony-B
Tony-B

Posted: Wed Mar 11, 2009 7:54am

Post Subject: Hull Blacking

Trouble is that I suspect (not having done it) that the test may give similar results to the first timer on both coatings. They say wet some rag with white spirit and then either leave it on the blacking and see if the blacking softens or rub it over the blacking and see if any comes off on the rag. I can foresee that the dirt and oxidation on a tar based blacking might make it look as if the actual blacking was coming off. Thats the best I can do - sorry.

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