Removing rust on cast iron drainpipe

Chloe_G

How should I remove the rust on my cast iron drainpipe?  Someone told me to buy Kuruste but I have also seen Hammerite rust remover gel. Is there any difference?  Thank you.

grumpy_codger

Depends on how much rust is there. Chemicals are good for removing small amounts of residual rust. Big amounts have to be removed mechanically - with a wire brush, angle grinder.

Section62

grumpy_codger said:

Depends on how much rust is there. Chemicals are good for removing small amounts of residual rust. Big amounts have to be removed mechanically - with a wire brush, angle grinder.

Also, why is it rusting?  If the pipe has cracked then clearing surface rust won't do much good, the rust will start forming under the new paint.

CliveOfIndia

grumpy_codger said:

Depends on how much rust is there. Chemicals are good for removing small amounts of residual rust. Big amounts have to be removed mechanically - with a wire brush, angle grinder.

^^^ This.  Most of the rust-killing chemicals are much of a muchness, to be honest.  Kurust is made by Hammerite, but for painting on to a vertical pipe, the gel might just be a bit easier to apply.

But if it's anything more than surface rust, personally I'd be tempted to remove the worst of it with a wire brush first, before applying the chemical (assuming it's not rusted right through).  If you've got an electric drill, a wire brush attachment will cost you a couple of quid, and will make it a lot easier if there's a reasonable area to be tackled.  If you do this, please make sure you wear goggles.  Many years ago I was doing something similar, managed to get a flake of rust in my eye (I was young and foolish at the time, didn't think I needed goggles).  My God, I never want to go through that pain again - it taught me a valuable lesson!

Eldi_Dos

CliveOfIndia said:

grumpy_codger said:

Depends on how much rust is there. Chemicals are good for removing small amounts of residual rust. Big amounts have to be removed mechanically - with a wire brush, angle grinder.

^^^ .  Many years ago I was doing something similar, managed to get a flake of rust in my eye (I was young and foolish at the time, didn't think I needed goggles).  My God, I never want to go through that pain again - it taught me a valuable lesson!

If you have to go for a MRI that is one of the questions they ask you on their checklist, yet one more reason to wear eye protection when necessary.

Chloe_G

Thank you. I don't know why it's rusting but it must be 86 years old and it's rusting at the base shortly before it goes into the drain. I have had a go with a wire brush but I'm definitely going to get goggles before I do anything else!

twopenny

I had the same problem in the same area.
I sanded it down and used car body fibreglass and resin to fill a couple of holes. Then some metal primer to get colour.
I did a proper job with undercoat and gloss but that needed redoing too often. 
So I used because I didn't have much time, multi surface paint (Bedec is the one I use regularly for metal) and that lasted really well. Also quick and easy to touch up if needed.
Brushes rinse in water 

I used hammerite on a metal outdoor light and the rust returned quite quickly. Brushes are ruined or you pay for thinners.

I've also tried coach paint on cast iron which should hinder rust but only a tad longer. Not worth the effort 

Chloe_G

I've never heard of Bedec but I've looked at their website and it sounds really good.  It only seems to be stocked in timber merchants around my way though.

Section62

Chloe_G said:

I've never heard of Bedec but I've looked at their website and it sounds really good.  It only seems to be stocked in timber merchants around my way though.

Toolstation sell it.

But as Bedec multi surface paint is water-based, it wouldn't be my choice of paint for rusting cast iron in an outdoor location.

Having cleaned to bare metal I'd apply a traditional solvent-based red oxide metal primer, then undercoat/topcoat using solvent-based outdoor grade paints.

Alternatively, if it is only the bottom which needs treating (say up to 12" from ground level), then some people would use a bituminous paint.  The advantage of this it it stays slightly flexible so is less likely to crack, and is a bit more resistant to knocks and chips.  It doesn't look pretty, so using it at a higher level from the ground wouldn't be a good idea. More importantly, if the rust is caused by the pipe being cracked then bituminous paint won't be affected.

I take twopenny's point about brushes, but for this type of outdoor work you don't need a high-quality brush - you can get cheap ones for about £1.  If you carefully wrap the brush in clingfilm after use then it should be fine to use for a second coat the next day.  Then throw it away.  I still feel uncomfortable at the idea of throwing away paintbrushes after so little use, but it isn't such a bad idea when you think about it.

twopenny

Section, I found that it was now more expensive to clean paint brushes than buy new cheap ones for outdoor work.
Times change 

Bedec multi surface, I think there are others but not many, I've used on metal garden furniture, cast iron gate and small fixings on cast iron guttering, pipes.
It lasted better and is a moment to touch up .

I have ordered online for a colour that couldn't be got locally.
Not cheap but don't mind when it makes work easier on several projects. Delivery was good direct to the firm.
 It lasts well in the tin so there's no waste.

There is a small size becoming harder to get and goes a long way.
I was lucky and just paint everything soft white 😊

Haven't tried any other multi surface as I'm many miles from the big stores but would be interested for a comparison.

Murmansk

My understanding is that cast iron doesn't rust very much which explains why many old cast iron drainpipes that clearly aren't painted on the inside, and have water flowing down them, are still here after a hundred years. The balcony at our place has cast iron brackets holding it up which date back to 1893 and they're still going strong.