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I've tried using sodium hydroxide (NaOH) to clean mold (mould) in the shower before on a patch test area, and it worked really well. This simply involves using drain cleaner (with gloves, open window etc.) liberally on a scourer, and just wiping it on the tiles, plastic shower pan etc. I waited for ~20min, then used the shower head to spray it down the drain.

I understand that NaOH is highly corrosive and would easily eat into the skin, however it is intended to be used as a drain cleaner. Thus presumably it's OK on plastics used in pipes such as ABS and polypropylene.

Qs: Are there any gotchas (unintended side-effects) that I should be aware of with this method? Is this OK to use on silicone and grout?

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  • All answers so far are really informative (from a health/toxicity perspective), and welcome. I haven't had any comments on the effects of silicone and plastics from use of NaOH (i.e. damage, if any), though... – CJBS Apr 25 '16 at 16:25
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    Are you cleaning the mold, or are you cleaning the shower? :P – isherwood Apr 25 '16 at 18:25
  • @isherwood This is mainly with regard to getting rid of mould. I can scrub/wash to get rid of soap scum and water mineral build-up separately. I don't want to be using a chemical which will damage the shower enclosure itself. – CJBS Apr 25 '16 at 21:22
  • I tried cleaning grout in my bathtub with lye. I scrubbed and scrubbed using a concentrated solution, and the black mold did not come off. The latex based caulking was not affected by the lye either. It remained adherent and did not soften. After rinsing the area, it looked the same as before. – Martin S. Mar 30 '18 at 19:35
  • Why not use TSP ; a much better cleaner and not as caustic ? – blacksmith37 May 20 '18 at 18:58
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I'm a materials scientist, and I can tell you that the main plastic components used in plumbing products are generally polyolefins (polypropylene, polyethylene and polybutylene etc...). They are highly chemically inert to caustic solutions so you shouldn't have any problems there. PVC is not quite as resistant but for the short periods of time you are looking at during cleaning with an NaOH solution, there should be no issues. Similarly, silicone sealant used for baths is a cross-linked silicone elastomer and is also inert to caustic solutions. I'd advise that after washing rinse thoroughly with water. Most metals and alloys are fine except Aluminium; which could rapidly corrode.

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I think you are right to use caustic. NaOH is fantastic. It comes with some positives that outweigh the negatives in your case. Peroxyacetic Acid or Peracetic acid, they are the same, come with some things you should know about.

It's an explosive acid. The guys who have jet packs and fly around. They burn this stuff. I have found that small doses dropped on the ground, can be very toxic in unventilated areas. I have been around for accidents where we were forced to clear entire floors of people for 2 plus hours for spilling as little as 8oz. Just like hydrogen peroxide sold at your Walgreens, this stuff is the same, just much more concentrated. Often the stuff in the store is sold at 3% and Peroxyacetic acid is often 25% concentrations of hydrogen peroxide. It also will have some acid affect on your grout and tile. I would be more cautious of acid on grout than caustic.

Benefits of the Peracetic acid solution include:

  • Extremely short contact time needed to kill germs. They use this stuff in chicken plants.

  • Breaks down into harmless vinegar and water given time.

  • Extremely small amounts needed at 25% concentration. 1oz per 6 gallons of water to create a sanitizing solution. You dont need much. 5 gallons might cost you 150 dollars. IT will last for 3840 gallons of sanitized water.

Caustics include there own benefits.

  • They are great at removing protein. They are used in major brewing, dairy, pharmaceutical and other food production facilities. They clean things. Wet things. Mold like things.

  • When mixed with chlorine they can kill bacteria and mold, and work at a lower temp. Do not mix chlorinated caustic with any acid. You will make mustard gas.

  • Do not use purple cleansers. They are usually made with high concentrations of nitric acid which will also degrade your tile or concrete. Don't mix purple cleansers with chlorinated anything.

Remember that straight NaOH isn't a sanitizer. It is a cleanser. Most commercial examples are blended with a chemical that is probably known to someone to cause cancer. It has all sorts of industrial uses. If you need to sanitize your bathtub, cause your are making gin or something you could sanitize it with H2O2. I think that would probably be bad for your biom though and I don't think you should sanitize. Cleaning and scrubbing with high powered lye cleaner will do you just fine. Remember to rinse. Also remember to be soft on your grout with the brush and keep the temp on your wash bucket really hot. As hot as possible. Most of that stuff is meant to work at 120-160+ degrees depending on how it is blended. Hot caustic means less scrubbing, more waiting followed by washing off.

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As someone who is a student of chemistry, I would say that lye is not toxic, it's caustic. In fact, it's less toxic than Tylenol, mg for mg. This doesn't mean it isn't dangerous; concentrated sodium hydroxide is quite hazardous, but is safe to dispose of by rinsing with plenty of water (you can't overdo it).

Sodium hydroxide breaks up organic matter by attacking the cell membrane. Long story short, it turns the fats that make it up into soap. From there, it's all water-soluble and goes easily down a drain. Of course, your body is made of cells too, so it'll do the same thing to you. This is also why if you were to touch lye beads (do not do this) they would feel greasy, as the lye breaks down the dead skin layer on your fingers.

To those that say that sodium hydroxide does not sanitize, you're wrong. If you wash something that's made of cells with sodium hydroxide, it will be dead. It's roughly equivalent to sanitizing something with boiling water, it completely destroys cellular matter (basically anything that's alive).

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    Hello, and welcome to Stack Exchange. There's great information here, but unfortunately it doesn't answer the original question (does NaOH harm plumbing and shower parts). – Daniel Griscom Apr 25 '16 at 19:18
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Slightly off topic, but if you are looking for a good product to disinfect your shower and clean mould, I would seriously consider Hydrogen Peroxide.

The H202 structure of Hydrogen Peroxide means that its just an unstable form of water with one extra oxygen molecule. When, oxidisation occurs, one extra oxygen is released, so, all you smell will be oxygen.

Its also way cheaper to NaOH, non toxic and can be used almost anywhere.

Sodium hydroxide is a strong alkaline, and reacts to acids and is effective to break down oils, and scale, But beware, it will burn your hands, its a good idea to wear gloves and if you get some on your hands, wash with vinegar water solution.

The NaOH will clean the grout really well, but it will weaken and you will get soft grout essentially many grout cleaners use NaOH as an ingredient. I think for a once off clean (provided you work in a really well ventilated area, and use all the protection, you could use it as an initial clean) thereafter i would switch to H2O2

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    Please note, you still need to wear gloves with hydrogen peroxide. One of my pool chemicals is 30% strength h2o2 and if a small amount of residue gets on my skin, it will burn it almost immediately. – diceless Jan 8 '15 at 20:32
  • true. anything more than about 5% requires gloves. – Hightower Jan 9 '15 at 7:21
  • Thanks for the response. Any idea/experience on the use of NaOH on silicone (caulking), or the plastic liners of shower windows, etc.? – CJBS Jan 12 '15 at 21:54
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    @CJBS - sorry, no real experience there, we can wait for the chemical experts to respond, however the inertness of both silicon and rubber on the shower windows should almost certainly be fine. – Hightower Jan 13 '15 at 7:39
  • @Hightower Thanks. BTW, NaOH is super-cheap when bought for $1 per litre as part of a generic drain-cleaner solution at the dollar store. It's the main active ingredient. – CJBS Jan 13 '15 at 16:51

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