When the obvious answer is wrong

Sometimes the treatment that removes the problem is the treatment that ruins the surface it is on. These are the cases where the obvious answer is wrong, and what to do instead.

• How do I remove limescale from a marble shower without ruining the marble?

  Limescale on polished marble · A different kind of treatment works

  Marble is also calcium carbonate. The acid cannot distinguish between carbonate deposited by hard water and carbonate that is the stone itself, so it dissolves both. The result on the stone is etching: a dull, slightly rough patch where the polished surface has been chemically removed. It is not a stain and there is nothing left on the surface to clean off.

  The damage cannot be undone by cleaning.

• Can I use a limescale remover on the grout in my shower?

  Limescale on grout · A different kind of treatment works

  Cementitious grout is alkaline based and is dissolved by acids — the tile trade states this plainly and draws the conclusion itself, that manufacturers do not advocate acids because they attack the cement in the grout. Grout is also porous, so an acidic product does not merely touch the surface. The damage is gradual and looks like wear rather than like chemical attack, which is why it is rarely attributed to the cleaner that caused it.

  The damage cannot be undone by cleaning.

• Can I use oven cleaner or a strong degreaser on aluminium?

  Grease on aluminium · A different kind of treatment works

  Aluminium is amphoteric — attacked by strong bases as well as by strong acids. The alkali dissolves the protective oxide film and then the metal beneath, leaving a dull grey or blackened surface that is not a deposit and cannot be cleaned off. There is a second consequence that is a safety matter rather than a cosmetic one: a US state hazardous substance fact sheet records that sodium hydroxide reacts with metals including aluminium to form flammable and explosive hydrogen gas, which is not what anybody expects from cleaning an oven tray in a confined space.

  The damage cannot be undone by cleaning.

• How do I get rid of rust that keeps coming back on a chrome fitting?

  Rust on chrome plating · This is damage, not dirt — cleaning is the wrong approach

  Where the plating has been breached, the rust is not sitting on the surface — it is the steel underneath corroding and showing through. Removing what is visible does nothing to the corrosion producing it, and the treatments make the situation worse in two ways: an acid or chelant reaching bare substrate through a breach attacks it directly, and abrasion widens the breach that let moisture in. The mark returns, faster each time.

  The damage cannot be undone by cleaning.

• How do I get hard water spots off a bathroom mirror without wrecking it?

  Limescale on mirrored glass · A different kind of treatment works

  A mirror is not a pane of glass. It is glass with a reflective coating and a protective backing, and both are exposed at every edge. The glass industry's mirror division states that acid or alkali cleaners can attack the front surface, the edges and the backing, and names cleaners containing ammonia or vinegar specifically as ones not to use. The failure is called black edge, it starts where liquid runs into the perimeter, and it is degradation of the mirror rather than dirt on it.

  The damage cannot be undone by cleaning.

• Can I use a limescale remover on my bathroom taps?

  Limescale on plated and coated tap finishes · A different kind of treatment works

  The visible part of a modern tap is a plated, physical-vapour-deposited or powder-coated finish a few microns thick, not solid metal. The manufacturer's care sheet states that PVD finishes must not meet cleaners containing ammonia, bleach or acid, which excludes most limescale removers and a good share of bathroom sprays. Because the finish is microns thick there is no margin: material lost is coating lost, the dulling is progressive, and it cannot be polished back because there is nothing underneath to polish.

  The damage cannot be undone by cleaning.

• How do I get a grease mark off suede without ruining the nap?

  Oil and grease on textile on suede · A different kind of treatment works

  Suede is the porous lower split of the hide with nap on both sides, dyed like aniline and uncoated. The trade guide states that cleaning agents will immediately darken nude leather — there is no cautious first application, because the first application is the result. Water is not a safe alternative either: the guide specifies deionised water because hard water containing minerals may cause rings. And the guide separately prohibits alcohol, strong solvents, high-pH cleaners and dish detergent on leather generally, as incompatible with modern finishes.

  The damage cannot be undone by cleaning.

• Can I use oven cleaner on the burnt-on mess in my self-cleaning oven?

  Burnt-on food and carbon deposits on vitreous enamel · A different kind of treatment works

  The manufacturer prohibits it in absolute terms: no commercial oven cleaner or oven liner protective coating of any kind should be used in or around any part of the oven. The mechanism is delayed rather than immediate. RESIDUE FROM OVEN CLEANERS WILL DAMAGE THE INSIDE OF THE OVEN WHEN THE SELF-CLEAN CYCLE IS USED — so the harm happens later, at pyrolytic temperature, to whatever the cleaner left behind. Someone who sprays, wipes and sees nothing wrong has not shown the practice is safe; they have postponed the test. The same guide notes that even soap left on the liner causes additional stains when the oven is heated.

  The damage cannot be undone by cleaning.

• Can I leave a cast iron pan to soak to get the burnt-on food off?

  Burnt-on food and carbon deposits on seasoned cast iron · A different kind of treatment works

  Cast iron is bare iron protected by a layer of polymerised oil, and that protection is defeated by water rather than by scrubbing. The manufacturer's wording is blunt: SOAKING CAST IRON IN WATER IS A RECIPE FOR RUST. It extends the same warning to cookware left in the sink to soak, put in the dishwasher, allowed to air dry, or left in a moisture-prone environment — and states that a dishwasher will remove the seasoning and likely cause rust. The failure is not the burnt food coming off. It is that the pan is left in prolonged contact with the one thing its finish exists to keep off it.

• What should I use on red wine spilled on a wool carpet or jumper?

  Red wine on wool · A different kind of treatment works

  Wool is a protein fibre and oxidising bleaches attack it directly, degrading the keratin rather than the stain sitting on it. The damage is structural and it is not a mark that can be cleaned off afterwards: the fibre is weakened, and on a carpet the affected area wears differently from everything around it. The wool body approaches this from the other side, warning that methods aimed primarily at cotton or synthetic garments are not all suitable for wool.

  The damage cannot be undone by cleaning.

• What should I use on a greasy mark on a wool jumper?

  Grease on wool · A different kind of treatment works

  Wool is a protein fibre, and the mechanism that converts fat to soap also hydrolyses protein. A strong alkali therefore attacks the garment on the same chemistry it uses on the stain, and the damage is to the fibre rather than to its appearance — it is not a mark that can be cleaned off afterwards. The wool body approaches the same problem from the other end, warning that methods primarily aimed at garments made from cotton or synthetic fibres are not all suitable for wool, and specifying a dilute wool detergent in TEPID water rather than anything stronger or hotter.

  The damage cannot be undone by cleaning.

• How do I get limescale off a shower screen without damaging the glass?

  Limescale on glass · It cannot be removed safely — prevent it instead

  The glass association's cleaning paper excludes acids from glass cleaning solutions as a class, naming hydrochloric and hydrofluoric as its examples, and warns that glass can be permanently damaged if it is infrequently or improperly cleaned. It also rules out the two things people escalate to when the acid does not work: abrasive cleaning materials, and razor blades or metal scrapers, which are excluded from routine cleaning altogether. The mechanism it gives for scratching is not the cleaner but trapped grit, so scrubbing a gritty screen is worse than leaving it.

  The damage cannot be undone by cleaning.

• How do I get tarnish off silver-plated cutlery without wearing the plating through?

  Tarnish on silver plate · A different kind of treatment works

  That sentence is also the problem. Tarnish CONTAINS silver, so removing it always removes a little metal, and abrasive polishes carry corrosive acids as well as abrasive compounds. On solid silver that is a slow recurring cost. On plate the silver is only microns thick, so the same treatment is a countdown - and the museum sheet records how it ends: over-polishing plated silver removes the plating and exposes dull base metal that CAN BE MISTAKEN FOR TARNISH. The reader then polishes harder, on the one area with nothing left.

  The damage cannot be undone by cleaning.

• How do I get a greasy mark off a leather sofa arm?

  Oil and grease on textile on finished leather · A different kind of treatment works

  The leather trade body prohibits both by name, and the reason is the finish rather than the hide. Modern leather finishes are WATER-BASED, and its banned list is built around what attacks them: any high pH cleaner, cleaners containing alcohol, strong solvents, and caustic household cleaners such as soap or dish detergent. The stated consequence is cracking or other damage to the surface. It is the same reason saddle soap and mink oil are on the list beside glass cleaner - traditional leather remedies formulated for finishes no longer used.

  The damage cannot be undone by cleaning.

• How do I get grease off a vinyl seat without leaving a mark on it?

  Grease on coated upholstery · A different kind of treatment works

  The coated-fabric trade body classifies vinyl, polyurethane and silicone coated fabrics as SOFT-SURFACE materials despite their being smooth and non-permeable, and states that hard-surface cleaners, sanitizers and disinfectants are not intended for soft surfaces and could damage them. It then names hand sanitisers among the substances that STAIN coated fabric. So the alcohol wipe that removes the grease is on the list of things that mark the seat, and the mark it leaves is not a soil sitting on the coating that can be wiped off again.

  The damage cannot be undone by cleaning.

• There is a greasy mark on my aniline leather sofa. Can I use a leather cleaner on it?

  Oil and grease on textile on aniline leather · A different kind of treatment works

  Aniline leather is not finished leather. The trade body describes it as porous and DYED rather than coated, and states plainly that cleaning agents will immediately darken nude leather. There is no surface film between the cleaner and the hide, so the liquid goes in rather than sitting on top, and the darkening is absorption into the leather rather than a residue that can be wiped back off. The prohibition list this catalogue carries for finished leather is about protecting a water-based FINISH; aniline has no finish to protect, which makes it more vulnerable rather than less.

  The damage cannot be undone by cleaning.