The Chemistry of Cleaning #3: How to Clean Shower Screens

Last Monday on 6PR a caller on 6PR asked Shannon Lush how to clean shower screens.

She advised against using commercial products and instead suggested vinegar.

Let’s have a look at it. Exactly what is the grime on shower screens?

There are essentially two components of shower scum – mineral deposits (usually calcium carbonate) and soap scum. Soap scum is either the calcium or magnesium salt of the soap molecule.

Either way, the deposits are alkaline.

So to get them off, you need an acid. It needs to be a strong enough acid to dissolve the alkaline salts, but not so strong that it’ll either etch the glass or attack the alloy trim in the shower.

As it happens, there is only one acid strong enough to etch glass – hydrofluoric acid – and it’s certainly not sold over the counter to the general public. Other strong acids – hydrochloric and sulphuric acids – are available over the counter, but they would attack the metal in the shower recess so we won’t use those.

Vinegar – or acetic acid – is not a bad option, but a better option is sulphamic acid (found in BAM and also a toilet cleaner that Bunnings sell). It’s a stronger acid, will get the alkaline salts off easier, but won’t damage the metalwork.

But whatever you use, you may find that it never comes quite clean, and appears to still have deposits on there.

This is caused by the soap scum etching the glass. Soap is make from caustic soda and fat, and so the salts of the soap are highly alkaline. And glass is much more prone to etching by caustic soda than any acid. Anyone that works in a lab knows that you don’t store solutions of caustic soda in glass.

So the highly caustic soap scum will etch the glass. So even after you clean it off, you can still see the etching behind that it has left. I suspect this is what Shannon Lush calls “glass cancer“: But unfortunately her advice to use Goanna Oil won’t make a scrap of difference

So the lesson is – don’t let highly caustic soap scum build up on your shower screen – keep it clean

9 thoughts on “The Chemistry of Cleaning #3: How to Clean Shower Screens

  1. I agree. No amount of vinegar or bicarb soda will ever remove the soap and scum build up on glass. I find cleaners like Jif, a scratchy pad and a lot of elbow grease the best, but if the glass has been etched it will never be clear again. I clean rental homes for a living and see so much filth it’s unbelievable that people can let their showers (and the rest of the house) get so bad.

  2. Does this mean that I should probably stop using the sodium hydroxide glycerol byproduct (that I use for cleaning just about everything) on my glass shower screen, mirrors and windows? It would be a shame, as it works a treat!


    • You make biodiesel do you? Yep that stuff sure does work a treat. I should post my own biodiesel methods up some day

      • No, I don’t make it – I tend to be absent-minded, and I don’t trust myself with the chemicals! I get it from people who do make it.

        So should I keep the glycerol away? I think my screen has etching, but not sure if it was there before I started using it to clean with, or if it’s happened since then.

  3. BTW, I’ve learned to be careful of aluminium frames with that stuff…

  4. I have found my answer for the shower screen problem. Use liquid soap only in the shower. (Not my brilliance btw). It works really well!! The claim is that hard soap contains fat which causes scum.
    Some general washing down still required of course for any mould buildup but no scrubbing, and now have clear screens. Whoopee!

  5. I tried the Shannon Lush way. White Vinegar. Followed by wiping with Sweet Almond Oil. All it did was make it worse. It Smudged the Scum now my Shower Doors are Worse.

    • I’m not surprised. Acetic acid (vinegar) is far too weak to use on soap scum – the best stuff is sulphamic acid (BAM Easy Off). And it beats me why anyone would recommend almond oil for shower screens.