Cast iron scrap: why it is priced on its own, and how to get more for it

Why heavy cast iron pays less than steel

Cast iron is one of the most misunderstood grades in scrap. It is heavy, it is plentiful in old houses, garages and workshops, and it is genuinely recyclable. But it is priced as its own category, usually below clean heavy steel, and the reasons are about how it is made and how it is remelted, not about it being somehow lesser scrap.

What cast iron is, and why it behaves differently

Cast iron is an iron alloy with a high carbon content, typically somewhere between two and four percent, whereas steel has far less. That extra carbon is what lets iron be poured into a mould and set into a complex shape, which is why engine blocks, pipes and machine bodies were made from it for generations. It also changes the character of the metal. Cast iron is hard and wears well, but it is brittle. Under a heavy blow it cracks or shatters rather than bending like steel does.

For recyclers, that carbon content matters. Most steel scrap is melted in electric arc furnaces to make new steel, where the aim is to keep carbon low and controlled. Cast iron adds carbon, so it is usually directed to foundries that make new castings, or blended carefully in small proportions. A smaller set of buyers wants it, and they need it separated from steel, which is what the price reflects.

Where cast iron comes from

Engine blocks are the item most people meet first, though be careful: many modern engines have aluminium blocks, which are non-ferrous and worth more per kilogram. A magnet settles it in a second. Older pipework, from the era before plastic pipe, is often cast iron. Heating equipment such as traditional radiators and boilers is another source, as are the heavy machine bases and housings found on older industrial equipment, which are usually recognisable by their rough, grainy finish.

Because these items tend to be heavy and awkward, many people only encounter cast iron during a renovation or clear-out, when a lot of it turns up at once. That is when knowing how it is priced is most useful.

Five ways to tell cast iron from steel

Why it prices below clean steel

Three things push cast iron's price below grades such as HMS 1 or structural steel.

Its remelting route is different. Because of the carbon content, cast iron does not go into the same furnaces as most steel scrap. A narrower set of buyers, mainly foundries, creates less competition for it.

It is awkward to handle. Cast iron pieces are often bulky and irregular, and brittle, so they are harder to process and pack than steel plate. Large items have to be broken or cut to furnace size, and that takes labour.

It is often contaminated. Engine blocks arrive with aluminium parts, rubber hoses and oil. Baths carry enamel. Pipes may have lead joints or concrete. All of these reduce the clean weight and the grade.

None of this means cast iron is poor-quality scrap. A clean, sorted load of cast iron is perfectly good material to the right buyer. It simply sits in its own price category, and the best results come from selling it that way. For the exact movement of that category, check the live reference rather than assuming a fixed relationship to steel, because the gap changes with foundry and steel demand.

How to get the best price for cast iron

• Keep it in its own pile. A load mixing cast iron with cleaner steel is usually priced at whichever component is worth less. Separate it before you arrive or before you list.
• Strip the non-ferrous attachments. Remove aluminium brackets, brass fittings, rubber hoses and plastic. An engine block with an aluminium sump or manifold still bolted on will be priced as mixed or contaminated material.
• Drain it. Engines and gearboxes should be drained of oil and coolant. Many yards will not accept them wet, and you should dispose of the fluids properly.
• Check size limits. Yards and foundries often specify a maximum piece size. Very large items such as baths may need to be broken, and a buyer who does it for you will price in the labour.
• Know what you have. Say clearly in a listing whether it is engine blocks, pipe, mixed castings or a particular machine, and give an honest weight.

Breaking cast iron is dangerous. It shatters, and the fragments are sharp and fast. Always wear eye and face protection, gloves and sturdy boots, and keep bystanders clear. If the item is very large or you are unsure, let the buyer handle it.

Frequently asked questions