Needle Scaler

[PeteCooper]

Has anybody used a needle scaler to prepare a cast iron keel - and how successful was it?
I am asking as on a recent thread a couple of people are saying it didn't work for them. I was going to hire a needle scaler to prepare mine before painting on some zinc rich epoxy - but if a needle scaler won't do it then it's back to the drawing board.

 

[ganter]

I would have thought it would do a pretty good job - if not a rather long one.

I've read about using large 40-grit flap disc an angle grinder. I'll watch this thread with interest.

 

[David2452]

I have seen (and heard) people using them on steel hulls in the yard outside my office/workshop, bloody noisy but they seem effective.

 

[Rigger Mortice]

Has anybody used a needle scaler to prepare a cast iron keel - and how successful was it?
I am asking as on a recent thread a couple of people are saying it didn't work for them. I was going to hire a needle scaler to prepare mine before painting on some zinc rich epoxy - but if a needle scaler won't do it then it's back to the drawing board.

I was one of those who was disappointed with the results.

My only advice to anyone considering hiring one is to make sure that, if it is pneumatic, that the compressor is big enough to do the job. I suspect that the one I hired with the scaler just wasn't up to the job. I suppose I should have complained to the hire people but I just put it down to experience and got the angle grinder out.

 

[PeteCooper]

My only advice to anyone considering hiring one is to make sure that, if it is pneumatic, that the compressor is big enough to do the job.

The one I'm thinking of hiring is electric - so it might be OK?

 

[Rigger Mortice]

The one I'm thinking of hiring is electric - so it might be OK?

I'm sorry but I just don't know. I would guess that, if it has a small motor of say 6 or 700 watts, it won't be up to much. If it packs some punch then it will probably be fine.
Needle guns are certainly used in industry so they must be OK. It's just that my experience was a bit disappointing.

 

[lynall]

I use a small sealey air powered one at work and its really good for getting rust and corrosion off truck hubs ready for the new discs.

 

[Searush]

I hired one for the keels on SR (a Pentland in case anyone has forgotten ) It was electric & came with a big transformer(?). I had wanted an oblong brush style one, but they only had a needle gun, which looks like a big drill with about an inch diam head of needles. Because of the small area, it takes a long time to cover the side of a keel, but you can lean on it to apply extra pressure in the bad places. I did all 4 keel sides in a day (9.30-4.00) including hire & return.

Obviously you need goggles, & gloves help reduce the vibration. It removed all the loose flakes very well & even broke thro into a couple of small voids in the casting (2-4mm irregular bubbles in effect) but didn't produce the bright metal finish I was expecting. The end result was an irregular pock marked rusty coloured surface with some areas almost polished. I filled the voids with epoxy & gave it a couple of cots of Primocon, then "red lead" (yup, that's what it was sold to me as, but I doubt that it was) followed by a singe coat of a/f.

The final result looked OK but not quite as smooth as a babies bum, I really laid the paints on thick on the rough areas & that filled some of the pock marks, but I wasn't interested in fairing the keels with resin filler & sanding anyway. Now, about 4 years later, it's still OK with just an odd small bit of rust showing thro in a couple of spots. If I was going to a/f this year it would cover them up again, but this year I will only be scraping them clean on a nice beach somewhere in the summer sun.

Bear in mind that this is a 1973 yacht.

part- Finished keel (unpainted), area to right has been "needled", area to left is untreated in any way;

Needle gun;

Before I started.

 

[forelle541]

Yes that's the same Hilti one that I have, great on steel, just dents cast.

 

[AntarcticPilot]

The end result was an irregular pock marked rusty coloured surface with some areas almost polished. I filled the voids with epoxy & gave it a couple of cots of Primocon, then "red lead" (yup, that's what it was sold to me as, but I doubt that it was) followed by a singe coat of a/f.

The final result looked OK but not quite as smooth as a babies bum,

This is becoming a family problem - I too am looking to prepare my cast-iron fin keel for epoxying, along with the rest of the underwater hull! As mine is in preparation for Coppercoat, I have a strong interest in ensuring the finish is as good as possible to ensure the longevity of the Coppercoat - I want it to last me out.

I'm a bit concerned at Searush's description of the finish achievable with a needle gun. The ideal is supposed to be a bright finish, which has to be epoxied very quickly after the preparation to avoid "flash rusting". At least, that's what people who seem to know what they're talking about suggest. So if the finish achieved with a needle gun is rusty coloured, that suggests it isn't good enough for a reliable epoxy coating.

I must admit that after my previous enquiries about antifouling removal, I'm beginning to go back to considering getting it done by a professional blasting outfit.

 

[Rigger Mortice]

I must admit that after my previous enquiries about antifouling removal, I'm beginning to go back to considering getting it done by a professional blasting outfit.

If you want a no holds barred top quality finish then blasting is the way to go.

 

[oldharry]

If you want a no holds barred top quality finish then blasting is the way to go.

Correct. A needle gun is next best, but will not give a bright finish in my experience, leaving a coat of what i can only describe as rust dust. What they are very good at is removing scale and loose rust back to a sound surface.

The problem with wire brushing or angle grinding is that if the surface is pitted - and it will be if the rusting is at all advanced, rust will remain in the pockets. Grinders particularly can smear the metal over a rust pocket concealing it, and giving the impression all the rust has been removed which in fact remains, and reactivates as soon as moisture gets to it.

I have only used needle guns on steel plate, and am not at all sure they would be very effective on cast iron. With a casting only chemical removal or shot blasting is likely to be 100% effective.

 

[William_H]

I did a friends steel keel with an angle grinder with very course sand paper disc on a rubber backing pad. Very quick very easy. I think a wire brush on the angle grinder would get into deep hollows. I just have the feeling the nail gun would simply hammer the rust into place rather than get it out. But I have never used one. As said get the rust treatment on if you are using it then epoxy as soon as possible to avert more rust. good luck olewill

 

[mbay]

Pete you could do worse than the Perago scraper drill attachment i mentioned in my thread, As i said i was looking for alternatives as the perago is quite pricey but it did do a canny job. The one i bought was just the single but it did do the whole keel (Elizabethan 31) back to nice and shiney in a day. http://www.cirrus-systems.co.uk/perago-rotating-blaster-discs-2 http://www.youtube.com/watch?v=T4zrr0ONeA0

 

[GHA]

If you want a no holds barred top quality finish then blasting is the way to go.

Worth bearing in mind that it's probably not possible to know what just how much contamination is cast into a keel with the iron, if it's dirty then even the very best preparation might be money down the drain, it might still corrode.

 

[owen-cox]

I have to say from some recent experience with a twisted wire wheel on a grinder it is fantastic at removing paint and filler and rust. they are dead cheap too at about £4 from the usual non marine suppliers. I would highly recommend having a go with one of them before hiring anything in it works a treat on vehicle bodies.

 

[rob2]

I like the twisted wire brushes too. I wonder whether following up with a rust converter would deal with any contamination?

Rob.

 

[GHA]

I like the twisted wire brushes too. I wonder whether following up with a rust converter would deal with any contamination?

Rob.

From experience the wire wheel on a grinder doesn't get into the pores. With what looks like shiney steel on a very hot day, ospho (phosphoric acid) pops and fizzes with unseen rust in tiny pores. Seems to last very well, is it better to paint over iron phosphate or iron oxide? 6 years some patches above the waterline are lasting well.