Mould, mildew and damp

Where the obvious answer is wrong

Cases where the treatment that removes the problem is the treatment that ruins the surface it is on.

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

  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.

Assessed and found wanting

Widely repeated techniques in this area that the evidence does not support, or supports only in part.

• Spraying hydrogen peroxide and vinegar in sequence

  Does not work

  Circulated as a two-step method precisely because neither ingredient seems like anything to worry about. Together they form peracetic acid, which irritates eyes, skin and lungs.

• Following bleach with an alcohol sanitiser

  Does not work

  Doing both to be thorough is the reasoning, and the two react. Hypochlorite with alcohols forms chloroform.

• Vinegar as an all-purpose cleaner

  Disputed

  Genuinely excellent at one job and promoted into a universal one. The surfaces it is most often recommended for online include several it permanently damages.

• Using a limescale remover on shower grout

  Does not work

  It removes the scale and dissolves the grout. Cement is alkaline, and the tile trade says acids attack it — which is what most bathroom products are.

• Mould needs bleach

  Does not work

  The environmental regulator does not recommend biocides as routine, directs detergent and water, and says the part everyone misses: killing mould is not enough, because it must also be removed.

• Steam mopping a laminate floor

  Does not work

  The European laminate producers' technical bulletin has one categorical sentence and this is it: steam cleaners are not suitable for use with any type of laminate floor.

• Putting a cleaning block in the cistern

  Does not work

  The manufacturer's instruction is not that it works poorly. It is that it can damage the flush valve and other working parts.

• Combining bleach and hydrogen peroxide

  Does not work

  Two oxidising bleaches, so the reasoning is that together they must whiten harder. The regulator lists them as incompatible with each other.

• Bleach ruins outdoor fabric

  Does not work

  On solution-dyed acrylic the manufacturer specifies bleach, at a stated ratio, for mildew. That permission comes from how the fibre was dyed and does not transfer to fabric that looks the same.

• Running bleach through a washing machine to clean it

  Disputed

  It removes the smell for a while, and the trade's own evidence is that the growth is a biofilm on wet surfaces the water barely touches.

• One spray for the whole bathroom

  Does not work

  The most consequential belief in the house, because a bathroom puts five materials with contradictory rules within arm's reach of each other.

• Freezing kills mould

  Does not work

  Widely believed and specifically contradicted: freezing DEACTIVATES spores without killing them, and warming reactivates what survived.

• Killing the mould solves the problem

  Does not work

  The assumption behind every mould product. A federal agency states plainly that killing mould does not eliminate all health hazards, because inactive mould still causes reactions.

The records

• Mould

  Stain or problem

  A living growth, not a stain. Killing it and removing the staining are two separate jobs, and neither addresses the moisture that caused it.

• Mildew

  Stain or problem

  The flat, powdery surface growth that appears on damp fabric, grout and shower curtains — and the carpet trade's procedure for it names no bleach at all.

• Silicone sealant

  Material or surface

  The flexible bead round a bath or a worktop, and the most common place a household meets mould it cannot remove — because the growth is inside the material.

• Bath sealant

  Component

  The most common place a household meets mould that will not go away, because the growth is inside the bead rather than on it.

• Shower curtain

  Thing to clean

  Permanently damp, rarely dried and almost never washed — which is why it grows the thing people then try to bleach off it.

• Moisture control

  Method

  The treatment for mould that is not a cleaning product. Every authority in this register puts it first, and it is the only one that stops the problem recurring.

• Moisture control and recurrence

  Science

  Three separate health authorities lead with the same instruction, and it is not a cleaning instruction: fix the water. Clean without fixing it and the mould comes back, and the cleaning was never the failure.

• Dehumidifier

  Equipment

  Not a cleaning tool at all, and the most effective single purchase against mould — because it treats the cause the spray bottle cannot reach.

• Mould remover

  Cleaning agent

  Usually a bleach in a thickened spray. It removes the stain reliably and does nothing at all about the reason the mould is there.

• Biofilm

  Science

  Bacteria that have built themselves a protective matrix and stuck it to a wet surface. It resists disinfectant far better than the same bacteria loose in water.

• Grout

  Material or surface

  Cement-based grout is porous and alkaline, and acids dissolve it. That single fact rules out most of what bathroom cleaning advice recommends for it.

• Borax for mould

  Claim or technique

  Promoted as the gentle alternative to bleach, and the register can neither confirm the efficacy nor endorse the framing.