For La Cornue cast iron grates worn or rusted, the decision is simple: light surface rust can usually be cleaned and oiled, but a grate with pits you can feel, one that rocks on its feet, or one that is cracked should be replaced. Our care guide says a grate is finished when rust has gone past the surface and left pits you can feel with a fingernail, or when it rocks on its feet after cleaning, because a grate that does not sit flat will not hold a pan flat either. Grates are replaceable parts, and replacing one is a simpler fix than living with a burner that never lights cleanly.
Is a rusty La Cornue grate worth saving?
If the rust is light and on the surface, yes. Our burner caps and grates care guide explains that cast iron rusts within a day if it is left wet, and that a bare spot is treated with a thin wipe of cooking oil. Let the grate cool completely first, because cold water on hot iron can crack it. Wash it by hand with a soft brush or nylon pad and dish soap, dry it completely with a towel and let it air-dry until no moisture is left, then wipe a thin film of oil on bare iron. That is a cleaning job, not a repair.
Do not use steel wool, scouring powder or acid cleaners, and never run a grate through the dishwasher, which strips the protective film and leaves the iron chalky and gray before it shows orange rust, per our care guide.
When is a grate past saving?
Three signs tell you. First, rust that has gone past the surface and left pits you can feel with a fingernail, because those pits hold moisture and keep rusting. Second, a grate that rocks on its feet after you have cleaned it, because it will not hold a pan flat. Third, a crack or a broken foot, which is a safety issue because a heavy pot of hot liquid sits on it. A grate in any of those conditions should be replaced, not nursed along. If you are not sure, set the grate on a flat counter and press at the corners; any rocking means the feet or the body is out of true.
What causes grates to wear and rust?
Our care guide gives three sources, in order. Salt water is first, because brine from a stock pot or a pasta pan is the most common liquid to boil over and the most aggressive to leave behind. Acid is second: lemon juice, tomato, wine and vinegar all attack metal and creep under the edges. Standing moisture is third and the most avoidable, such as a grate put back damp or washed at night and left to dry in place. Our cooktop corrosion page says the same about caps and grates: it is largely cosmetic, but buildup can affect flame distribution if it blocks ports.
Heat discoloration is different. Brass caps darken where they run hottest, and that is normal wear, not damage. Do not polish it away.
Do you need to replace anything else with the grate?
Check the burner cap and crown underneath. The care guide notes that where a cap has been damaged, the crown beneath is worth checking at the same time, because the two wear as a pair. A rusty grate sitting over a cap with a chipped enamel edge or an enlarged port suggests the burner has been exposed to the same spills. A flame that looks different from its neighbors after replacement is a hint that a port has been damaged; our yellow flame guide explains what to look for.
How do you get a replacement grate?
Grates are model-specific, so match the part to your model rather than to a photograph. Our parts and national service center guide explains where to source La Cornue parts, and a technician can order and fit the right one. Do not try to bend, weld or file a cracked grate. We do not quote prices here; a technician confirms an estimate before any work begins, and a grate is a modest part compared with a range.
Is it a repair at all, or a part swap?
It is a part swap. Nobody repairs a cracked or pitted cast iron grate: you replace it. That is good news, because grates are simple, replaceable parts that do not touch the gas system. You can lift them off yourself once the burners are cool, and fitting a new one is the reverse. What takes judgment is deciding when. Because a worn grate can sit unevenly, a pan of hot liquid may tilt or slide, and that is a safety risk, not a cosmetic one. If one grate is badly worn, look at its neighbors; grates that have lived in the same spills for the same years tend to wear together, and replacing a set can be tidier than replacing them one at a time. Whether that is worth it is your decision, and we do not push it.
If a burner has started to behave oddly at the same time, perhaps with a weak or lopsided flame, the cause may be a cap or port rather than the grate, which is why we suggest checking underneath. Our clicking igniter guide covers burners that will not light after cleaning.
How do you stop it happening again?
Wash grates by hand, dry them completely, oil bare iron lightly, and wipe up brine and acid spills the same day. After a boil-over, do not leave the grate sitting wet. If your grates are on a French top or around a module that is seasoned, see our French top seasoning guide, because that plate is cast iron too and has its own routine. A grate that is replaced should be kept dry from the first day.
