Mini sandblaster for rust spots on keel?

[Sea Change]

Everybody tells me that the best way to prep the boat for a change of antifouling is to get it blasted. That's not an option for various reasons.

We've had some success using a formic acid based stripper followed by 80 grit, but when it comes to the cast iron keel I'm pretty wary. I don't want to expose any more bare metal than necessary. Fortunately the keel is currently in very good condition with just a handful of very small (coin sized) isolated rust spots.

I'm thinking about getting one of those super cheap handheld blasting guns just to hit the rust spots. My understanding is that grinding doesn't really eliminate the rust, and only blasting genuinely works. I know they're almost toys and you wouldn't do a whole body with one, but I've been seeing people on YouTube using them to strip things like bike frames, and they seem to work ok, just a bit slow.

Anybody tried using one?

Any suggestions for which media to use?

 

[MoodySabre]

I don’t think that you will completely stop rust on a cast iron keel. Use an angle grinder with a flap wheel. Zip off the rust, immediate coat if rust converter then underwater primer and AF of choice. Next year some other bits will be rusty….

Full blasting and exopy might last longer.

 

[Graham376]

I have one, OK for small areas of light rust. I used angle grinder on keel rust patches and immediately treated with rust converter.

 

[rogerthebodger]

Any grit blasting is better than grinding with an angle grinder as it gives any metal a better service preparation for the adhesion of any protective coating. I grit blasted my steel boat and coated the hull with epoxy tar. Preparation is the key

 

[Sea Change]

I don’t think that you will completely stop rust on a cast iron keel. Use an angle grinder with a flap wheel. Zip off the rust, immediate coat if rust converter then underwater primer and AF of choice. Next year some other bits will be rusty….

Full blasting and exopy might last longer.

I don't lift out annually so I'm looking for the longest lasting solution that is available to me.

Judging from your username, do you have a Moody? We had one previously and the keel was very rusty. We have a Jeanneau now and it seems to me that the quality of the cast iron is better. I was very happy with the state of the keel when we lifted out.

 

[Sea Change]

Any grit blasting is better than grinding with an angle grinder as it gives any metal a better service preparation for the adhesion of any protective coating. I grit blasted my steel boat and coated the hull with epoxy tar. Preparation is the key

What's your medium of choice?
In addition to the little rust spots on the keel, I have some flecks of the old AF on the hull which might be worth a tickle with a blaster too. I'm finding that trying to get at these last little pockets results in taking off a disproportionate amount of the epoxy barrier coat underneath. A gentle media blast seems like a good idea on these areas.

 

[geem]

My pal used a flap disc on a grinder on his Fulmar keels. As soon as he had done it, he epoxy primed them, then toweled on an epoxy filler to build up a thickness. It lasted several years. I think the key was in the thickness of epoxy he achieved.

 

[lustyd]

toweled

Trowel?

Gotta be careful though, if you fully encapsulate an iron keel in epoxy it could just end up being a pool of rust inside that you can’t see under the epoxy. I prefer paint so I can see damage and address it.

 

[KevinV]

I bought one of the little blasters and it's useless - not the thing itself but the amount of air you can flow from a small compressor.

 

[Sea Change]

I bought one of the little blasters and it's useless - not the thing itself but the amount of air you can flow from a small compressor.

Yes, they seem to need 10cfm+. I'm going to look in to hiring the compressor.

 

[penberth3]

I bought one of the little blasters and it's useless - not the thing itself but the amount of air you can flow from a small compressor.

So it's only useless if you use the wrong compressor? Is that what you're saying?

 

[Refueler]

My experience with mini blasters was not so good ... the amount of sand or grit needed was far more than imagined ... plus of course the need for ample air drive !

My preferred way would be to go with what we used on ships .... Needle Gun ....

These batter the surface - cleaning it up and leaving it to spec A2.5 ready for priming ...

 

[KevinV]

So it's only useless if you use the wrong compressor? Is that what you're saying?

They're sold as a light DIY tool, but won't work to any useful degree on a DIY size compressor - so I'd indeed class them as useless.

 

[Refueler]

They're sold as a light DIY tool, but won't work to any useful degree on a DIY size compressor - so I'd indeed class them as useless.

Its surprising how much air ... CFM .. is needed for various air tools .... I have a handy sized proper Hyundai Compressor that serves as my 'garage' unit ... but it cannot run a small paint sprayer unit ... which I was surprised at.

 

[Freebee]

I have used a mini sandblaster that attaches to a pressure washer, the feedstock was builders sand, it needs to be very dry so that it feeds properly into the suction pipe, it used a lot more water and sand than I anticipated and of course that is left on the ground all round where you are working. it removed rust and scale but patience was needed as it does not happen very fast.

 

[geem]

Trowel?

Gotta be careful though, if you fully encapsulate an iron keel in epoxy it could just end up being a pool of rust inside that you can’t see under the epoxy. I prefer paint so I can see damage and address it.

But if it worked for years then the proof is there that it worked. No blisters. Bare steel or cast iron is best treated with epoxy. And corrosion would be evident at lift out as the corrosion causes a blister and swelling, that would be visible.
He applied the epoxy with a spatula then sanded it smooth once cured, so yes a trowel if you prefer

 

[PCUK]

+1 for a needle gun.

 

[Tranona]

Trowel?

Gotta be careful though, if you fully encapsulate an iron keel in epoxy it could just end up being a pool of rust inside that you can’t see under the epoxy. I prefer paint so I can see damage and address it.

That is highly unlikely to happen if you prepare it properly and coat it immediately. How do you think water is going to get at the iron if it coated in epoxy? Failure is usually localised where adhesion is poor and tends not to creep under the surrounding coating.

 

[lustyd]

How do you think water is going to get at the iron if it coated in epoxy?

Any edge or crack would let a small amount in, that will cause rust and expansion which will spread, sucking in ever more water until the whole thing becomes a soggy johnny around a keel that you can no longer see or maintain.

Happens all the time to things covered in plastic. Powder coated metals often show this exact behaviour. Your mistake is in believing the epoxy will permanently adhere to a degrading metal.

 

[lustyd]

But if it worked for years then the proof is there that it worked.

The only way to tell if it worked is to remove the epoxy coating. It’s entirely likely that there’s iron soup underneath if it’s thick plastic.

I asked trowel because you said he towelled it on, which made no sense to me