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

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

  1. i’ve got shower screen scum and i’ve tried a lot of products, but i’ve never heard of glycerol,an at the moment i’m trying ceropal,i’v had these scum stains for many years,it’s only now i’m more determent than ever to get rid of it. what’s amazed me is that from day one we always hose of the soap from the glass screen after avery shower,so it has to be water scum as well.i’m open to suggestions.

  2. Have tried all sorts with Gumption being the best up to date but still some glass cancer visible. A relative’s shower was so bad he was considering replacing the glass. I suggested trying a safety blade to scrape off the worst and he was prepared to take the risk with scratches. It can be done on a dry screen or a wet screen with pros and cons for each approach. 95% removed by scraping, the other 5% with Gumption. Perfectly clean screen, no glass cancer and no scratches. Tried it on my own and same result, glass cancer gone.

    • Well done. But it’s not cancer. It’s a chemical compound of some sort. But you’ve answered a question for me – I thought it was etching, but if it can be scraped off it clearly isn’t. Steel wool may also be worth a shot. Contrary to popular belief it won’t scratch glass

      • All the information I have is that was a razor blade. If you scroll through the questions in this section you’ll find it eventually.

  3. I am a house cleaner and I have another theory I would like your opinion on. I usually see this effect on the area closest to the shower head and when the water is really hot. My theory then was that it was caused from really hot water hitting the glass or whatever the glass is treated with. I would have thought if it was caused by a cleaner or soap scum it would be more patchy. Thank you

    • Hot water won’t damage glass, although I suppose that with enough exposure there could be some mechanical scouring occurring

  4. Once you have your screen clean Polish it with a cream car polish. I use nu finish.
    You will find once you have finished showering the glass has steam on it. Steam has no impurities in it so no spots. Do not be tempted to spray the screen with hot water to remove the steam as you are adding more impurities . Just finish and walk away I think you will be pleased with the results with the car polish.

    • Good idea. It adds a silicone coating like Mr Sheen, but it’ll be a thicker coating so it won’t need to be reapplied as often

  5. If you google glass cancer there are several utube videos up that show how to remove it.
    I just purchased “Bar Keepers Friend” from “Kichen Warehouse” online.
    Well it works!! The dry pastier the better.
    It doesn’t come straight off & the first application only gets a very minimal amount off which looks like it doesn’t work. I just did a small 10cm square & repeated the process about 4 times. Def has removed most of it & there’s no etching lines in most areas of that patch even when viewed from above so you can see down the glass. Not going to lie & say it’s easy as it is a slow process to get the layers of the build up from the hard water off.
    But I’ll be persisting as it bugs me. It’s only happened in my boys shower as they got slack, in the other showers we squigee all the time after a shower & they are regularly cleaned.
    Def worth buying as it’s not expensive & it would have multiple uses around the house. I’m very particular with cleaning & this does get it off.

    • I saw that product in Coles last week – right next to the Brasso. But it’s not “cancer” – it’s etched glass, and yes, the right level of mechanical abrasiveness could certainly remove it

  6. I have travertine tiles on the bathroom and shower floor so need to be careful with products. (Not my choice, btw). Definitely no vinegar I’m told. Would Bam Easy Off be ok, because some is bound to get on the travertine.
    Thanks for the great advice.

    • No reason you can’t use vinegar. It’s weaker than all the acids used in bathroom cleaners. BAM would also be ok

  7. I just bought a place which had been rented prior to purchase, and found this exact problem with the glass shower screens. Then I tried a WD40 equivalent – Selley’s RP7. It removes the white “frosting” effect of the etching. The etching effect is still visible, but it is more of a “clear cut glass” look- which is a lot less noticeable. well worth it as a short term fix. You don’t need to rub hard either and the result is pretty much immediate. Just leave it long enough to dry.WDE40 products are water-repellent, so it’s a useful shower cleaner already.

    • It hasn’t removed the frosting – it’s just filled in the valleys. But it’s not a bad idea. The other thing that could work is a silicone-based automotive polish. Or Mr Sheen. But be careful you don’t get the silicone polish on the floor – it’s very slippery

      • Ok so I have a completely clean glass screen when wet and feels super clean to the touch. However when it dries you can see the white water marks that seem cloudy. I have tried every possible suggestion but it seems I have this shower cancer as they call it. How can I make it not so visible. Do I use the WD40 spray on them leave??

        • If you have tried a good quality bathroom cleaner like Ajax Spray & Wipe Bathroom, then it has been etched. The term “glass cancer” was invented by Shannon Lush because she doesn’t know anything about the chemistry of glass. What has happened is that the glass has been etched by the alkaline soap scum, as glass is prone to etching by alkaline materials. As far as covering up the etch mark goes, I’d try Mr Sheen.

  8. I own a cleaning business and it baffles me the amount of time I see this issue and sometimes I have to inform them that this is never coming off. It pays to clean your shower and blinds regularly and floors!!!!! These are the main areas that need attention on a regular basis. You don’t realise how much grease can build up on blinds and how much damage your shower can obtain from saying ” I will do it next week
    ” because let’s be realistic, if your are time poor for cleaning it will come back and bite you. Renters and owners need to be aware of it. Cleaning is a long term investment and a short term reward

  9. 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.

  10. 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!

  11. 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.

  12. 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.

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