Keeping rust at bay

[Petronella]

What's the best way to keep the rust at bay on a steel boat?

Preparation. Chip or sand?
Acid etcher?
Primer?
Paint?

Petronella has a two part epoxy paint topcoat so that has to be the final medium.

Thanks for any advice.

John

 

[peterbringloe]

First of all try to attend to any rust as soon as possible.

Grind back to bright metal and treat with a phosphoric acid based product (I use Ospho). Then apply your paint system - primer, undercoat and top coat.

Obviously try and do the job in good weather.

If rust is coming from something bolted to the deck for example, you must remove it and treat and paint the area including the holes before re-fitting. Painting up to the edge of the stancion base or whatever is unlikely to be successful.

Try and deal with as much as you can in one go. And be methodical at every stage. When using two part products this is especially important. I have found it a real pain to mix small quantities. Also, unless you are very careful when storing it, the hardener can go off and you are left with just the paint. With International Perfection (our paint system) you can't buy just the hardener (at least I couldn't find it).

I use an angle grinder with a flexible sanding disc. It can be a bit brutal for small areas and not easy to get to awkward places. I wish I had a small pad with small discs. I bought a Dremmel-like tool with a load of little sanding discs etc for dealing with small areas but it's not really powerful enough - you end up bringing out the big guns!

If you grind too deep you may have to use an epoxy filler before painting.

This is probably all pretty obvious so apologise if I'm teaching you to suck eggs.

 

[mireland]

Where do you buy Ospho please?

 

[Wino]

The only way of ensuring rust removal is by grit blasting. I f you grind you can not get deep enough into the pores of the steel without removing loads of the surface. From working on many ministry rust removal contracts when they always state grit blasting - as do all shipping companies - I know that that is the only way of getting a good result. Knowing how mean our MOD is with money I am sure if they thought grinding was OK they would do it.

 

[peterbringloe]

Mireland - Ospho is widely available in the Caribbean and USA but I'm sure that any of the acid based rust curing products (they turn rust black) will do. After getting back to bright steel you shouldn't have any rust left to turn black - but apply it anyway.

Roj1 - I'm sure you're right, grit blasting would be best. But for steel boat owners who are trying to keep on top of small areas of rust that appear from the odd scrape or chip it's not possible, unless there is a small portable grit blasting machine available that could be used with precision - a bit like the thing dentists use to squirt water when filling your teeth!

 

[Pasarell]

As Roj1 said the best way is to blast and recoat properly but that is impractical for most small/medium repairs.
On large projects where blasting is not possible they normally use a needle gun. Very accurate and better than grinding. I'm sure you can get a small needle gun that would be suitable to keep aboard a steel boat but don't know where from.

In my experience the biggest reasons for rust reoccurring after preparation are not properly washing salt off first and then not getting primer on quickly enough or adequately. If I could get clean steel I would never acid etch, just go straight on with a good anticorrosive primer.