Best paint for cast iron?

[woodspiral]

Hi,

Last year I put cast iron guttering up. We gave it 2 or even 3 coats of primer (Bedec water based metal primer) and a couple of top coats of Zinsser AllCoat exterior satin, which I was assured by Brewers was the best thing to use for this application. Six months later rust started coming through in patches. I've attached a couple of photos to give the general idea. It seems to be happening most around contact points between brackets and the actual guttering itself, which may have occured when the guttering was installed (through small scratches etc).

I'm worried I used the wrong primer or top coat, or that I used paints from two manufacturers which might be incompatible.

Hopefully there is some remedy to this situation? Perhaps this is inevitable with cast iron? Perhaps my expectations of not having to paint for 5 years is unrealistic? Am I doomed to paint this guttering every year?

Would an oil based paint be better with a rust inhibitor like Owatrol? I'm hoping I can paint something on like Jenolite then use some rust-blocking/inhibiting paint on top.

I asked an engineer friend and he talked about powder coating. I'm not sure I can face taking it all down and installing it all again, so that's not really an option here.

Thank you
Woodspiral

 

[eribaMotters]

My initial thoughts are your choice of a water based primer. I use water based paints on everything inside and out, except when in contact with metal or when priming anything outside.
My fear is the only way to rectify the situation is removal of the guttering and taking back to metal before re-priming.

Colin

 

[Jacob]

Linseed oil paint for the outside. Very easy to apply and will cover rust and old paint well if loose stuff is well brushed back - no dramatic preparation required. Seems expensive by the tin but goes a long way, lasts a long time and is very quick and easy to use.
Bitumen paint for the inside.
PS painting white maybe not a good idea as every blemish will show. Black or red iron oxide better.

 

[AES]

I've found that a zinc-based primer (Hammerite, and there are others), followed by Hammerite colour - they do white - is the dog's do dahs (even the "new" Hammerite). It comes in both aerosol rattle cans and brush on (tins) but needs a special thinner (for brush cleaning) which here anyway is sometimes hard to come by.

And sorry, I agree with eribaMotters above, to me, the only way to really stop that problem is to bring the whole lot down, strip off the old and start again. A big job no doubt.

 

[Jacob]

I've found that a zinc-based primer (Hammerite, and there are others), followed by Hammerite colour - they do white - is the dog's do dahs (even the "new" Hammerite). It comes in both aerosol rattle cans and brush on (tins) but needs a special thinner (for brush cleaning) which here anyway is sometimes hard to come by.

And sorry, I agree with eribaMotters above, to me, the only way to really stop that problem is to bring the whole lot down, strip off the old and start again. A big job no doubt.

I've tried Hammerite. Wrought iron gates and some large cast iron decorative hinges and other ironmongery on a chapel door. Not as good as it is cracked up to be and linseed oil paint out performs it by far. Looks better too.
I've only used the Allback brand but there are others

 

[eribaMotters]

I also agree about Hammerite not being the paint of choice. It is great on machinery but it can crack and chip.
In the 80's I owned a 30's house with metal windows that had gone very rusty. I had to cold chisel out the rust, treat with Rust Cure, then a specialist primer and finished of with an oil based gloss.
The best I ever came across was Permoglaze. I don't know if it is still sold.

Colin

 

[mwinfrance]

2 pack epoxy paint..or 2 pack poly..strip back to bare metal and use the paint manufacturers primers..or hammerite and repaint every 3 - 5 years.
Personally I left all ours (' galvanised steel ) as galvanised ..no problems, or rust ..15 years ( they were actually fitted 10 years before we bought the place ) so 25 years.

 

[niall Y]

The last Hammerite paint I used was water based - both the primer and the topcoat

 

[mwinfrance]

The last Hammerite paint I used was water based - both the primer and the topcoat

Never seen any of that here ..all mine ( about 20 litres in various colours ) is all 'trad" formulation hammerite.

 

[niall Y]

Never seen any of that here ..all mine ( about 20 litres in various colours ) is all 'trad" formulation hammerite.

Sadly, all the new stuff is water based. I still have lots of the old cans in various colours. I believe it is all owned by AksoNobel now

 

[Jacob]

.....

And sorry, I agree with eribaMotters above, to me, the only way to really stop that problem is to bring the whole lot down, strip off the old and start again. A big job no doubt.

Not necessary with linseed oil paint. It covers old paint well, no need to strip etc, just clean up and brush off loose stuff.
I once had to replace some vandalised windows in a railway station (listed building, designed by Paxton's firm). The wood had many layers of paint going back to the original and had never been stripped. No doubt the metal work would be the same.
It explained a mystery I had come across years before when trying to repaint old stuff - if I burnt off the paint in the modern way I never seemed to see signs of previously having been burnt off. I was the first one to be doing it in 100 - 200 years! It still had all its old oil paint on, presumably with just a clean up and rub down between coats.
Linseed oil paints weather from the surface but never lifts off the wood or metal.
Modern paints the opposite - perfect surface even after it has lifted off with cracks and flakes and allowed water in behind. It then has to be removed, primed, undercoated, top coated. Non of those have to be done with linseed oil paints.

 

[AES]

Sadly, all the new stuff is water based. I still have lots of the old cans in various colours. I believe it is all owned by AksoNobel now

Sorry, never seen water-based Hammerite here (Switzerland). It IS a new formula ("improved" so they say - IMO it isn't!) but just from the smell of the above mentioned special thinners/brush cleaner, the stuff here is definitely NOT water-based. Can't explain it though - perhaps because we're not in the EU? Dunno, just a wild guess.

 

[mwinfrance]

EU here..never seen it either.

 

[woodspiral]

Thank you, people. I think I'll go with Linseed Oil paint for now and see how that works out. I definitely can't face taking it down!

 

[Jacob]

Thank you, people. I think I'll go with Linseed Oil paint for now and see how that works out. I definitely can't face taking it down!

No guarantees but it definitely works for me! I don't know what difference the underlying paint makes, but so far everything I've covered over seems to be weathering well.

 

[spanner48]

Probably the best is a zinc-rich 'Cold Galvanising' paint, applied to the individual carefully cleaned and derusted gutter sections. such as:

• Fosroc Galvafroid
• ZG 90
• Trade Paints 'Galvafroid Equaivalent'

No need to topcoat, unless you are in a notably acid environment. The zinc will weather to a dull, darkish grey.

 

[Limey Lurker]

Probably the best is a zinc-rich 'Cold Galvanising' paint, applied to the individual carefully cleaned and derusted gutter sections. such as:

• Fosroc Galvafroid
• ZG 90
• Trade Paints 'Galvafroid Equaivalent'

No need to topcoat, unless you are in a notably acid environment. The zinc will weather to a dull, darkish grey.

I used 'Galvafroid' many years ago as a first coat after alterations to steelwork. Undercoat and colour coat on top. Over 'bright' steel it is still good; over brushed rusted steel, and over sanded original paint it was a waste of time and money. (the 'bright'steel had the millscale removed for welding)

 

[spanner48]

Agreed. The key is the chemical bond bewtween the zinc in the paint and the raw steel. Any barrier - however thin, ruins the effect. Personally, I'd descale and scour clean and bright, THEN give it a pickle with strong hydrochloric acid – then rinsed off with nothing but clean water.

 

[thetyreman]

strip it back to bare metal, red oxide primer then paint it, you can get linseed oil red oxide primer but it's eye wateringly expensive.

 

[Jacob]

strip it back to bare metal, red oxide primer then paint it, you can get linseed oil red oxide primer but it's eye wateringly expensive.

From here about three times the price of Screwfix equivalent but still better value IMHO. Very high pigment content which means it goes a long way and just one coat will cover anything, even brushed thin - which you have to do anyway.