Best way to remove paint from cast iron bench ends

[Neil S]

Hi,
I'm restoring an old garden bench. It's the type with cast iron ends and wooden slats.
There's a lot of rust and flaky paint I want to remove. The cast iron is quite intricate with a lot of hard to reach areas. I've hit all the external surfaces with a preparation wheel in an angle grinder and its worked well.
Whats the best way to remove the rust and paint from the internal areas?

Can you use heat from a hot air gun or a blow torch? Could that crack the cast iron?

Thanks all

-Neil

 

[mikefab]

I'm doing a batch of these. Got them shot blasted at a fiver a bench end.

 

[julianf]

Would they fit in a 200ltr barrel?

If so, find a plastic barrel, fill it with water, and dump in a load of caustic soda.

When you're done, it may still be good for getting rid of the neighbours / your hands / your eyesight / etc.

For bonus points connect up a sacrificial anode and use electrolysis to remove the rust too.

Note - caustic does not seem to work on powdercoat, and some modern paints.

 

[novocaine]

small fire. as long as you heat it up in evenly and let it cool evenly it should be fine.

 

[Eric The Viking]

I used to do Victorian fireplaces with Nitromors, which got into the moulding detail beautifully, and had the advantages that it wouldn't promote rust, and didn't harm marble either.

You can still get the original formula under other brand names (IIRC it uses methylene chloride as the active ingredient) if you are a "professional restorer", it's not allowed to be sold to the general public.

Actual Nitromors exists in name only now - I've had no success with the eco-friendly formula but thankfully have no more fireplaces to restore!

If there isn't much detail in the castings, I'd go the sandblasting or beadblasting route.

E.

 

[julianf]

If you search dichloro-methane on eBay, you can buy it in 5ltr containers.

It's volitile, and, without the thickner that the "paint strippers" have, it won't be loads easy to use, especially as you won't want to get it on you, and it will eat through most PPE.

A curiosity is that it's not miscable in water, but, unlike most of those kind of things, it's density is greater than h2o. So people often put a layer of water on top of it, in their tank, to stop it evaporating.

I would have thought that the water coating on dipping (as the job passes through the water layer) would complicate things, but seemingly not.

If I ever get around to it, I plan on getting an HDPE drum large enough to just get an alloy wheel in, and spending out on some DCM to strip my landrover wheels.

I think that DCM will do powder coat also.

 

[Jacob]

Caustic soda good as mentioned above.
If you can't find suitable plastic container or old bath whatever, make a shallow tray with heavy duty polythene over a wooden frame.
best outside in a yard with a drain, hosepipe, etc
Hot air or blow lamp no use. The iron conducts the heat away and you may get cracks.

 

[ED65]

Caustic soda will work for getting the paint off most likely but it won't do anything to the rust, that has to be dealt with separately.

A good way to work with caustic soda on larger items where you don't want to risk working with such a large volume of a dangerous chemical is to use a spray oven cleaner that contains caustic soda (sodium hydroxide), such as the original formula Mr Muscle. That was my go-to paint stripper for years. Another option some of my friends started to use is Fairy Power Spray and I believe there's now a Tesco equivalent. These share the same active ingredient, but I don't know if the concentration is lower than in oven cleaner.

For the rust, if you can't see yourself going over the whole thing with a wire wheel or cup brush (which will take you approximately forever as you fear) soaking in a molasses solution might be something to look into as it's very cheap for large volumes. It will be slow though, especially now as we're heading into colder weather. And you will want to do this outside or in a garage you don't spend much time in as the smell is a bit of an acquired taste! The process could take a week or longer but it's very effective and very safe and if you forgot about the parts for a month they wouldn't come to harm.

 

[Neil S]

Thanks for all the replies.
I think I might give the caustic soda a try.

-Neil

 

[julianf]

Really, if you're going to use a caustic bath, find your old (non smart) battery charger and give electrolysis a go.

I've spent so long in the past with wire wheels and that, but now I know about electrolysis, I'd never bother with them.

The finish is so much better from electrolysis too. So much more complete. It turns the rust to a blackish grime that you just pressure wash off.

 

[Neil S]

Is there an electrolysis de rusting guide?
What sort of voltage and amperage should it be?
What metal should the anode be?

Thanks again.

-Neil

 

[Droogs]

big list of vids here https://www.youtube.com/results?search_ ... t+removal+

 

[julianf]

Is there an electrolysis de rusting guide?
What sort of voltage and amperage should it be?
What metal should the anode be?

Thanks again.

-Neil

I actually have a bench power supply doing mine, rather than a battery charger...

It will work at low amps but quicker at higher. My psu is said to be 8.5 amps, and has a thermal overload switch. So all I do is keep increasing the volts until it starts to shut down, and then back off a bit. I will check for you, but I suspect I'm running at around 10volts?

But what works for me at my temperature of electrolytes, my concentration, my surface area of cathode anode, etc. is only going to be a rough figure for you.

As for the anode - some bit of steel. Not stainless. Just a bit of old rebar etc.

People claim it's line of sight only, but it's not in my real world experience. Sure the stuff closest to the anode will be done first, but it's not just straight lines. You do not get rust "shadows" or anything like that. It's not nearly as complex as some would have you believe, with their multi anode setups.

Really, I have a 205ltr blue drum, with a bit of old steel (originally the side of a central heating boiler that I chopped up for something else) on the end of a wire dangling in, and an old "unilab" school bench power supply that I pulled out of a skip at my partner's work (cracked case, failed pat, noone bothered enough to do the simple repair)

 

[Neil S]

That's great thanks guys.
I have a battery charger and should be able to get hold of some caustic soda.

Gotta find myself a suitable shallow bath/bucket and I'm good to go.

Cheers

-Neil

 

[julianf]

To strip paint you need flesh melting concentration of caustic.

You don't need anywhere close to that for rust.

You may want to apply the caustic directly maybe with a binder, and then use a dip tank with lower concentration for the rust?

I mean you can do them both at once, but you would need a fearful (as in danger rather than cost) quantity of caustic for the dip tank.

I buy naoh in 25kg sacks for another process. It's cheap enough, but it still gives me the fear when there's a large dip tank of it at high concentration.

Some people use washing soda for electrolysis, but I've not found it as good.

Ps if you get any caustic on your hands, wash them until they stop feeling soapy. The soapy feel is the fats in your flesh saponifying to soap. Ie your hands turning to soap.

Wash until no longer slippery feeling.

Always add caustic to water, and not the other way round. Be careful of a lump on the bottom of a plastic drum as it's exothermic when it gets wet, and a solid lump can get hot enough to start melting the plastic if you're proper unlucky.

I mean it's fine, but you do have to be a little cautious with caustic.

 

[ED65]

The finish is so much better from electrolysis too. So much more complete. It turns the rust to a blackish grime that you just pressure wash off.

Just want to mention that the exact same is true of molasses solutions. Just a lot slower (usually, depends on your electrolyte concentration and power supply).

Head to head the two methods each have their plus and minus points, but especially if there are kids or pets in the mix a big vat of watered down molasses has one clear advantage! Even if you bump the container and spill some down your leg you're fine as the stuff is safe enough to pour directly onto the lawn.

 

[ED65]

Is there an electrolysis de rusting guide?
What sort of voltage and amperage should it be?

It actually doesn't matter that much, in the sense that many different setups all work just at different rates.

Weaker electrolytes and weak power supplies can still do the job, but obviously you'll get faster results with a stronger electrolyte and a more powerful power supply. As julianf says if using caustic soda the solution doesn't have to be strong enough to be dangerous, but you don't have to use it at all if you don't want to. As you'll see if you Google it, washing soda gives results just as good so if you want to err on the side of caution go with that.

Since it's getting colder, temperature is a factor too. Many users report it slows down noticeably if it's very cold, but it still works even close to zero.

What metal should the anode be?

Any old bit of iron or steel will do. Many use rebar these days because it's cheap and easy to get. Whatever you use just clean the surface off periodically.

Some sources strongly warn against using stainless as it's reported to produce chromium compounds which can be toxic, example.

 

[Phil Pascoe]

Ps if you get any caustic on your hands, wash them until they stop feeling soapy. The soapy feel is the fats in your flesh saponifying to soap. Ie your hands turning to soap.

Wash until no longer slippery feeling ...
.........................
That's interesting. For many years I used to clean beer lines, and the usual way to know when the detergent was flushed was to rub your fingers in the flow of water - when they stopped feeling slippery the job was done. I'm not sure now what the constituent of the detergent was but it was alkaline.

 

[will1983]

I restored this old bench earlier in the year.
It belonged to my partners Grandmother for many years and she spent hours sat in her garden on it so when she sadly passed away I decided to give it a new lease of life.

The bench ends were sandblasted and powdercoated at a local company. I derusted and painted the carriage bolts in bilthamber deox-c and hammerite.

Thee bench slats which I think are some sort of iroko were showing quite a bit of wear and weathering so I took them to a local joinery shop and begged the use of their wide belt thickness sander for 20minutes. Due to H&S I wasn't allowed to use it myslef but they very kindly offered to send them through for me. The edges I planed myself then gave everything a good going over with the sander. 3 thin coats of Blackfriars clear exterior varnish and it was set aside to allow the varnish to harden for a couple of weeks.

I reassembled it whilst my partner was at work so it was a nice surprise when she got home to find it in our garden ready for probably another 20 years of use.

The powdercoating is a nice job with no loss of detail in the casting and should lasts for years but I wish I had done some prep beforehand as the casting marks where the two halves of the mould meet is still evident despite me asking that they be ground off before coating. Total cost £70 for powdercoating and about £15 on varnish.