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We have a nice, recently redone bathroom that has a fan and nearby window. The shower is behind a glass door though with just a foot or so of space at the top though, so it probably doesn't get a lot of ventilation. After a few months, we saw dark dots on the ceiling.

We wiped it down with bleach and it came off easily, but only a few weeks later it's back. Is this a real concern or more just cosmetic? What's the best way to keep it at bay? We don't want to have to use bleach every time. Thank you!

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    that is what you fear most. But spray some bleach on it and check in 30 minutes if it is gone
    – Traveler
    Commented Jul 23, 2023 at 20:56
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    shouldn't be too concerned. you don't sleep in your bathroom but it doesn't look nice. i'd get a high quality anti-mold paint and paint it.
    – Fresh Codemonger
    Commented Jul 23, 2023 at 20:58
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    Does your fan move air? Have you verified its ducting?
    – Aloysius Defenestrate
    Commented Jul 23, 2023 at 21:09
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    Apart from checking that the fan is doing its job, you need to help it get the airflow through the right place. That probably means leaving the shower door open except when in use.
    – Chris H
    Commented Jul 24, 2023 at 9:11
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    @Nelson, I am still flagging your edits as "No Improvements", because there isn't. The review queue gives a false impression that things have improved, but they havent.
    – Rohit Gupta
    Commented Jul 25, 2023 at 2:54

4 Answers 4

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The is mold. You will need to scrape it off and repaint.

I think I have a couple of answers about this but I have redone quite a few bathrooms and I do one or another option below.

#1 Oil based primer. Then oil based paint. Mold will not stick to it unless the conditions are extreme. Even if it does get moldy unless just pure negligence, you can wipe it off (if white ceiling paint you can use bleach). This is my go to for bathroom ceilings. Just to be clear you paint your whole bathroom with oil based primer. Ceilings done in oil based paint. Walls can be latex.

#2 Oil based primer (two coats) and latex on ceiling. For large bathrooms with lots of ventilation I might do this.

If you put down a quick coat of latex primer then paint this is what you will get. Builder's grade bathrooms look like this and get moldy quickly. I don't understand the maybe 30 mins of time and $20 extra. You shouldn't have to redo bathroom ceilings. I do this in my rentals and never have issues. Ask people what they do with long-term rentals and you will get some best practices. Rooms shouldn't be built so you have to "be careful" all the time.

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It is mold.

Mold is typically present in bathrooms with inadequate ventilation.

The first thing you need to do is verify that your exhaust fan is working correctly, that the exhaust hose is not crushed if in an attic or that the exterior vent doesn't have louvers stuck, preventing proper airflow.

Second, determine the CFM (cubic feet per minute) of the fan and make sure it is up to par with the size of your bathroom.

When it comes to wet rooms the paint sheen plays a big role in preventing moisture penetration into the walls, you typically want an eggshell or higher (semigloss/gloss). I like to use a pre-catalyzed epoxy, it's pretty bulletproof.

Clean the mold with a bleach/water solution mixed 50/50 and apply a good stain blocking primer and your choice of topcoat, either a high sheen latex or the epoxy I mentioned earlier, I like Sherwin Williams Pro Industrial.

Sherwin Williams Pro Industrial

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In contrast with the other answers, I'm going to say that oil-based paint is not the answer, and in fact will often make the problem worse.

If you are getting mold, the issue is quite simply insufficient ventilation; You need to improve it by either getting a higher cfm exhaust fan, running it for longer, or fixing any other issue (blockage / vent location etc.) there is with the current setup.

If you use an oil-based paint, should you get any condensation, it will bead on the surface, and if not allowed to dry properly (due to the poor ventilation), this will allow mold to form. If you use a (porous) latex paint, if any condensation happens, it will simply be absorbed. If ventilation is poor, then this damp will also build up over time and cause mold. The thing is, that this will happen more slowly, because the surface moisture level will actually have longer to build up than than for a non-porous surface, allowing longer for the poor ventilation to actually dry things out.

Sure, it wipes off more easily from a shiny surface, but the trick is not to allow the mold to form in the first place.

I know people will disagree with me here, but in over 30 years of home ownership and four different bathrooms, the only time I have ever had ceiling mold is when I used an oil-based primer over some caulk before painting the whole with a latex-based paint; You could clearly see where it was by the black marks - the rest of the ceiling was completely mold-free.

Oil-based paints should only be used if there is no chance of achieving proper ventilation, and the only solution is regular wiping-down.

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    As a HO you can manage it. If you have a bathroom that is in near constant use - no amount of ventilation will be sufficient. The best thing is to treat it as a steam shower and tile the ceiling but short of that there are better paints with better mold inhibitors.
    – Fresh Codemonger
    Commented Jul 25, 2023 at 4:42
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One of the conditions encouraging mold growth is of course humidity from the shower. To address that, another option might be a dehumidifier, perhaps adding a fan for better air circulation.

Any such appliances would need a GFCI and to be situated out of the way of splashing water etc.

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