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Old 18-04-2019, 17:43   #16
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Re: She need new bottom paint

There is also the issue of what the cleaned surface is like. Grinding/sanding leaves a very different surface than that from sand blasting, and the latter is what is required for best coating adhesion. If you look at the parameters set by paint vendors, sand blasting is the method of choice.

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Old 18-04-2019, 22:46   #17
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Re: She need new bottom paint

Sorry to break you the bad news. You can grind away the rust and then treat the metal with phosphoric acid. After that apply the coatings. But this will only last for one or two years before the rust shows up again. It very feasible on deck to do this yearly, but not below the waterline.

The only option to PERMANENTLY get rid of the rust is to sandblast it. This is not very expensive. Then apply several coats of epoxy primer, tie coat if needed and antifouling in CORRECT film thickness.

My favourite primer is Intershield 300. The is an ablation resistant paint, so will not easily be damaged. Also, lasts VERY many years.
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Old 18-04-2019, 23:25   #18
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Re: She need new bottom paint

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Originally Posted by MartinR View Post
Sorry to break you the bad news. You can grind away the rust and then treat the metal with phosphoric acid. After that apply the coatings. But this will only last for one or two years before the rust shows up again. It very feasible on deck to do this yearly, but not below the waterline.

The only option to PERMANENTLY get rid of the rust is to sandblast it. This is not very expensive. Then apply several coats of epoxy primer, tie coat if needed and antifouling in CORRECT film thickness.
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My favourite primer is Intershield 300. The is an ablation resistant paint, so will not easily be damaged. Also, lasts VERY many years.
This . You may not like it but the initial cost will be less than a couple of years fluffing around with the same repeating problem.
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Old 19-04-2019, 16:20   #19
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Re: She need new bottom paint

Hey guys,

Thanks for all the replies, I’ve been quoted £2k for sandblasting, it’s my second option if the large wire brushes I’ve ordered for my angle grinder don’t work but I think they might and they should create enough coat adhesion. Hmm we’ll see.. be nice to save 2k though.
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Old 19-04-2019, 16:43   #20
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Re: She need new bottom paint

With rotating brushes you damage the cleaned surface of the steel, believe this dutch steel old sart..... sandblasting is the only way to prepare steel hulls.
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Old 19-04-2019, 19:48   #21
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Re: She need new bottom paint

You could use a needle gun but it will take a long time
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Old 19-04-2019, 20:23   #22
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Re: She need new bottom paint

If you insist on sanding, grinding and wire brushing you better be prepared to clean and prime every few square feet or you are really wasting your time as invisible oxidation (rust) starts almost immediately. This method will also waste a tremendous amount of expensive epoxy primer.
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Old 19-04-2019, 22:24   #23
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Re: She need new bottom paint

Coat adhesion is not the issue here. If there are any traces of rust left after wire brushing the surface will rust again. And there are always traces of rust left, even if they are microscopic.

2k seems cheap to me for sandblasting. The epoxy primer is expensive, so better to do this right, once.
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Old 20-04-2019, 08:11   #24
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Re: She need new bottom paint

Ok, just had it inspected and there’s good news

The only bit of rust is slight and on the keel, been told I don’t need to sandblast it
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Old 20-04-2019, 08:22   #25
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Re: She need new bottom paint

Thanks for the info on wire brushes for the grinder.. I really had no idea but I guess that’s why I’m here so much I still don’t know
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