Mold growth in my bathroom

Recently, I discovered mold growth in my bathroom due to poor ventilation. I've tried various DIY methods to remove it, but it keeps coming back. I'm concerned about the health risks and the potential damage to my home. What are the most effective techniques and products for mold removal, and how can I prevent its recurrence in the future?

Have you tried lemon juice, vinegar or baking soda aka bicarbonate of soda?

It sounds like you answer your question about the cause.

Here are some threads that might help you or others:

https://permies.com/t/6649/permaculture-home-care-cleaning/clean-mold-mildew-organically

https://permies.com/t/148893/permaculture-home-care-cleaning/Mold-removal

It may not be to everyone's liking, but I remember reading about a man (in Australia?) who used slugs to clean his bathroom. They came out at night when it was cool and dark cleaning up the mould, then lived in a little ceramic pot with holes in during the day. Definitely a bit far up on the weirdness scale though! I gather that European field slugs were the most effective, if you want to try and duplicate his little household helpers.
(Funny what sticks in my mind!)

Hi Michael,
Welcome to Permies!

Hydrogen Peroxide is a decent way to clean the mold, but the best way to kill it is to rob it of moisture. Most people use bleach, but that has too much water to be effective. I would triple check that the ventilation is the problem and that you do not have a leak somewhere, because the #1 thing to do when dealing with mold is to remove the moisture.

The first question that comes to mind is what surface is the mold on? If it is on something like sheetrock or a manufactured wood/glue panel of some kind, then it is very likely the mold is embedded and will be nearly impossible to kill completely without removal. If it is on something like solid wood or tile, then it should be just on the surface, and be cleanable.  

Matt McSpadden wrote: The first question that comes to mind is what surface is the mold on?  

I think this is a really important first step. Many treatments are only surface treatments, there are fewer that can go into material pores and deal with the mold. From there, an effective treatment plan can be better formed.

Nothing to back this up but a somewhat vague memory of being told that bleach is actually counterproductive in removing mold, but that vinegar is the way to go.

Except now that we know about pet slugs.....!!!  I think it would be a bit traumatic if one had to get up in the night, though. ... My imagination has taken this way too far!

Hi Adele,
The issue with bleach (at least the stuff normal people can buy) is that it is mostly water. And mold needs water to live. So you are just feeding the mold.

If it's a painted surface once you can repaint it with paint mixed with borax. Not completely non toxic but better than the mold. See if you can get a dehumidifier too.

Adele Poe wrote:Nothing to back this up but a somewhat vague memory of being told that bleach is actually counterproductive in removing mold, but that vinegar is the way to go.

This is an ongoing debate in my house. My husband insists on bleach, and I know it does zip.

I also recall reading that altering the pH of the surface is the way to go- either with baking soda or vinegar.

We do a lot of "make your own" cleaning supplies here and what I've found really good lately for my shower and grout is:
half dish detergent
half vinegar (i use white, buy it by the gallon for cleaning)

put it in a spray bottle and shake it up
spray down the shower tiles and grout, let it sit while you clean the toilet and sink

come back and scrub with a scrubby brush, rinse it all out

it works great, and if you don't like the smell of your dish detergent you can buy a neutral version and add a scent (that's what I do). I also can't see why you wouldn't be able to use a liquid soap like Dr Bronners if you prefer.

Tereza Okava wrote:
I also recall reading that altering the pH of the surface is the way to go- either with baking soda or vinegar.

Baking soda will make things alkaline, vinegar will make things acid....I'm just thinking aloud here, so bear with me. Mould is basically a fungus? So is clubroot on brassica. You are supposed to lime your soils to reduce the risk of club root, so logically baking soda would be more effective than vinegar, Hmmm. Not what you've found though, so I'm either completely wrong, or there is something else going on. Do we need Raven to chip in here....I'm thinking there may be some tips in her cleaners you can eat book?

My go to has been spraying vinegar for mold in a shower. I let the sit time go for about fifteen minutes. My lungs can't take the fumes of some of the powerful ick cleaners so I utilize vinegar. These however are not porous surfaces I work with. It wipes away.

Nancy Reading wrote:Mould is basically a fungus? So is clubroot on brassica. You are supposed to lime your soils to reduce the risk of club root, so logically baking soda would be more effective than vinegar,

Right! I'm thinking powdery mildew on my bean leaves, where I would spray milk, also a very weak base.

I've also used baking soda in the shower, but I don't have any stronger bases than that (easily accessible to me, anyway).
Vinegar is a relatively strong acid in comparison to baking soda as a base -- assuming that my knowledge of chemistry isn't totally off.

the way I see it is we need to tilt the scale in some direction, doesn't matter which one, to make the fungus less comfortable.

Black Mold is Aspergillus Niger so yes kicking out of it preferred Ph range isn't going to make it happy. There are also signs it can be inhibited with lactic acid bacteria might have to give that a go:
https://pubmed.ncbi.nlm.nih.gov/26597145/

I have found that after removing mould painting it with a thermal insulating paint solves the problem. "Theramix" is sold in a powder form which can be added to any paint.

There is an industrial paint made for this kind of application that I used to use and would consider again, if nothing else worked but a dehumidifier would take away the conditions it needs to thrive so you could actually get permanently rid of it.

I got told to open the windows after showering, then leave and close the door to keep the heat from leaving the rest of the house.
Cold showers generate less vapour, and wake you up a treat! I wouldn't take them in the colder months.
Get as much of the wet down the drain as you can: pre-dry yourself with a flannel and wring, shake the drops off your shower curtains, squeegee your cublicle...

the best solution I have used to remove mold on porous surface was 50/50 white vinegar and hydrogen peroxide. after scrubbing the surface to remove as much as possible I did repeated applications to keep the surface wet so it could penetrate the wood and the cement blocks in the basement. after many applications over a day I used a small ozone machine in the room for 24 hours.

Had the same problem. The problem ended up being the exhaust fan wasn’t rated for the bathroom size. The exhaust fans have a CFM rating that’s relative to the sq footage of the bathroom. Make sure you get something equivalent or slightly more. I got a CFM rating that was rated for a bit bigger of a bathroom. The other nice part of the fan is it has a blue light that’s supposed to help kill mold and bacteria.
We sprayed white vinegar on the ceiling and scrubbed the mold off. There’s an anti-mold paint specifically for bathrooms too.

Good luck!

I read once long ago that bleach will not actually kill mold. It only whitens the stain and may leave a residue that the mold can grow on (as does soap) Hydrogen peroxide will kill mold, but you may need to get something stronger than regular 3 %. I have been using 35% greatly diluted to 6% for many things, but I just discovered that on Amazon there are many brands of 12% H2O2. This would be a lot safer and easier to use than 35%. You might be able to find it in a hardware or home goods store.  The bottle should tell you how to dilute it , if necessary, for what ever use you need. Of course you have to keep the area dry. You can also buy de-humidifier buckets.

Zachary Bertuzzi wrote:Had the same problem. The problem ended up being the exhaust fan wasn’t rated for the bathroom size. The exhaust fans have a CFM rating that’s relative to the sq footage of the bathroom. Make sure you get something equivalent or slightly more. I got a CFM rating that was rated for a bit bigger of a bathroom. The other nice part of the fan is it has a blue light that’s supposed to help kill mold and bacteria.
We sprayed white vinegar on the ceiling and scrubbed the mold off. There’s an anti-mold paint specifically for bathrooms too.

Good luck!

Another thing to know about exhaust fans, they don’t necessarily get installed so that they exhaust to the outdoors, or even another space.  

Some contractors seem to believe the function of the fan is to provide noise to cover the noise normal to human elimination, farting and flushing the toilet..

Lydia Feltman wrote:I read once long ago that bleach will not actually kill mold. It only whitens the stain and may leave a residue that the mold can grow on (as does soap) Hydrogen peroxide will kill mold, but you may need to get something stronger than regular 3 %. I have been using 35% greatly diluted to 6% for many things, but I just discovered that on Amazon there are many brands of 12% H2O2. This would be a lot safer and easier to use than 35%. You might be able to find it in a hardware or home goods store.  The bottle should tell you how to dilute it , if necessary, for what ever use you need. Of course you have to keep the area dry. You can also buy de-humidifier buckets.

I just want to set the record straight about bleach, white vinegar, and hydrogen peroxide. All of them contain water! Household bleach is 6% sodium hypochlorite in water. White vinegar is about 5% acetic acid, and water. Household hydrogen peroxide is 3% hydrogen peroxide, and water. Even if you use a higher concentration of hydrogen peroxide, the reaction yields water and oxygen.

I agree that making an inhospitable pH might be the key to effectiveness. Bleach has a pH of 11-13 (very alkaline). White vinegar is about 2.5 (very acidic). Household peroxide is a weak acid with a pH of 6, but can be as low as 3 for industrial peroxide.

The thing to remember about mold is that spores are everywhere, not just where you see the mold. You can reduce them with treatments, but as long as you have the moisture problem, it will return. I agree with the dehumidifier idea and the practice of opening a window.

A quick question re opening a window:  if the humidity outside is high enough (say higher than 75%) will opening a window really make much difference?

 I've heard that not only does baking soda change the PH but as it dries it crushes the mold.
Every time it gets wet and dries, it crushes more.

I had a wall near the toilet with a light mold rainbow.
Cleaned it, painted it with bathroom mold paint and
sprayed it with BS water.
Kind of forgot about it. A year later I noticed there was no mold.

I know that would be a better test if I hadn't painted it.

Clove oil in vinegar works well

This is a timely forum post inasmuch as I have some mold to deal with, too

While surfing the interwebs I came across a very informative site - Mold Help For You. The site is provided by a Certified Mold Inspector from the International Association of Certified Mold Inspectors

There were many informative articles, including many of the topics discussed here, so you might want to take a look see

One, pretty comprehensive article, discusses both how to remove molds from the bathroom and how to keep mold from growing there is the following: Black Mold In The Shower? Here’s How To Remove It! | Mold Help For You - https://moldhelpforyou.com/shower-mold/

Hope this helps

We had severe issues with mold in our house when we moved in. It is an old building, poorly insulated, and with some areas that never get comfortably warm. For a while we heated just some of the main living spaces.

We found that the cold areas were struggling due to condensation as the warm humid area from the living spaces hit cold surfaces. We ended up with walls, ceilings, woodwork etc... black with mold. We cleaned all the mold thoroughly, and it hasn't come back. However, the reason it hasn't come back is that we dealt with the root cause of the issue - warm humid air hitting cold surfaces.

We couldn't do anything about the cold surfaces, so we made a concerted effort to deal with the humidity. We reduced the amount of clothes drying that we do indoors, and are more careful about ventilating when running showers and boiling in the kitchen. However the big difference came when we got a powerful dehumidifier and started running it round the clock in the autumn. During summer, when external temperatures were high, we had no condensation and so no mold. In Autumn we had humid warm air indoors, hitting the now cold surfaces. I started the dehumidifier and it showed the house consistently at 80% to 90% humidity. I was emptying between 5 and 7 litres of water per day for about two months.

Over time the frequency it needed emptying reduced, and the humidity indoors stabilised at around 50% to 60%.

My conclusion was that during the warm weather the humidity soaked into the fabric of the building - bricks, plaster, lime mortar etc... these act like sponges. So when the autumn came the house released that moisture back into the air, which caused the condensation problems. It was frankly remarkable how much water it pulled from the air - I probably emptied over 500 litres over a few months. Now, at the end of winter, the cold temperatures persist but the indoor air is dry and we have no condensation issues.

Bottom line, it seems like fixing a mold issue is really about fixing a moisture issue.

_____

Top tip - warm air holds more moisture than cold air. If you want to get rid of soaked in humidity you can try getting your house HOT for an hour or so. Then open all the doors and windows for 5 minutes to do a total fresh air exchange. Close everything up, wait an hour and repeat.

If you do this on a cold  and dry day, the air coming in will carry a lot less mass of water than the air leaving - even if they have the same % humidity.

Added bonus - a dry house is much easier to heat, and feel warmer, than a damp house

I am dealing with mold in our attic, due to the soffit vents being blocked by insulation.  I have been down a rabbit hole of research and, despite many opposing voices I have come to believe that any biocide is counter productive, due to the fact that killing mold spores breaks them into MUCH smaller pieces, called mycotoxins, and adds to the VOC load of the home.  These are more difficult to remove and can have even more detrimental health effects.  I would recommend you look up John Banta, a leading researcher on all things mold remediation, and home environment.  His website is a little clunky, look past the book info to his blog and articles!  but there is excellent information there.  There are also a few really good video interviews.  

The better health guy: https://www.google.com/search?q=john+banta+yourube&oq=john+banta+yourube&gs_lcrp=EgZjaHJvbWUyBggAEEUYOTIJCAEQIRgKGKABMgkIAhAhGAoYoAHSAQg0OTA2ajBqN6gCALACAA&client=ms-android-google&sourceid=chrome-mobile&ie=UTF-8#fpstate=ive&vld=cid:96367ef2,vid:i1sES9VWz_U,st:0

Good luck and keep us posted on the bathroom!

I don't think anyone has mentioned caulk yet. I had to rip out a shower due to a caulk fail that got out of hand. If the mold is growing around/in the caulk, the old caulk needs to be removed and redone. There's no good way to clean it once the mold has gotten into the caulk. There are various grades of caulk, some meant to last longer than others. The one you want should say 100% silicone somewhere on the bottle.

Thekla McDaniels wrote:A quick question re opening a window:  if the humidity outside is high enough (say higher than 75%) will opening a window really make much difference?

This is why I wish we all used dew point instead of relative humidity to think about water in the atmosphere.

Relative humidity depends on temperature. The warmer the air is, the more water it can hold. By using dew point as a measure, we can compare the moisture levels at different temperatures much more easily.

If the outside air is 5 C (41 F) a relative humidity of 75% means the dew point is 1 C (34 F). Warming that same air up to room temperature, 20 C (68 F) would give it a 28% relative humidity reading...quite dry. The dew point stays the same.

If you've just taken a nice hot shower the dew point in your bathroom could easily be 20 C or higher. As long as the temperature outdoors is lower than this (it's impossible for the dew point to be higher), you will get a benefit from opening the window (and you will see an impressive cloud form when you do if conditions are right). And if it's warmer outdoors, unless you're in tropical monsoon conditions, the dew point will still be lower than your steamy bathroom.