Tony-B...
Posted: Sun Jun 12, 2016 6:23pm
Post Subject:
Blacking
Blacking is a generic term covering loads of products so you need to understand exactly what you are looking at. Traditional blacking falls into one of two types, tar based or bitumen based. If you try to put tar based over existing bitumen the bitumen is likely to dissolve and shed the new tar based blacking. To test what you have rub the hull with a rag soaked in white spirit or at a pinch petrol. If the blacking starts to dissolve and come off on the rag its bitumen based. That means you should only apply a bitumen based blacking unless you want to blast the whole hull back to bare steel and start again. Bitumen will often cover well weathered tar based blacking with out problem but no guarantees. Black jack is a simple bitumen paint but for only a little more cost you can get modified bitumen like Premium that has more body and is a little better suited to hull work. I think Intertuf is the name of International's blacking lines and it is followed by numbers. These identify the product so as you do not give me the numbers I can not comment. Keelblack is a new product that is a bitumen in a water based body. IT is too new for their to be much user feedback but the claims made for it seem good if they are completely true for normal use. Probably the most long lasting "blacking" is one of the two part epoxy products but they should be applied to base steel so blasting is required. Although much tougher than ordinary blacking the coat is likely to be damaged by abrasion on lock walls etc. IN summary; find out what type of blacking you have, check out products using the same base and evaluate the claims made for it against the price. I do not recommend unless I have used the product but I find a modified bitumen satisfactory on my boat
