Mould or a sign of something worse?

[AllyP62]

The ceiling in my bathroom is turning black, but in sharp edged blocks in over the shower cubicle, in line with the ceiling rafters I think. There’s a working extractor over the bath in place but it does get steamy. What sort of professional checks this sort of thing out? builder?

Yes. But not the one who built it. Sounds like defective Chinese drywall was used for your ceiling which is illegal but some builders sneak it in because they have stocks of it. Here is a picture

I’ve only just registered on mumsnet so can’t post photo yet. Thanks in advance

Oh, sorry thinking US again. Probably not illegal Chinese drywall...but it does still sound like defective drywall or the wrong drywall was used. There is special moisture resistant (more pricey) drywall supposed to be used in bathrooms but they may have skimped and put regular drywall on your ceiling.

Ah, looks like you guys call drywall plasterboard in the U.K.
At least it still color coded the same. So in bathrooms, supposed to use green moisture resistant plasterboard...I did a search and it averages £15 a sheet compared to regular white plasterboard which is £5 a sheet. Properly entire bathroom should have moisture resistant plasterboard but some builders will skimp and only put it behind tile surrounds and regular stuff everywhere else including ceiling.

If you have warranty on home, you could pursue with builder. Otherwise, will need ceiling redone and make sure the moisture resistant stuff is used.

The first thing I would do is check the loft and in particular the area above the shower. Where does the extractor vent to? What depth is the loft insulation above the shower? Is it damp or are there any signs of a leak up there? Is the loft insulation pushed right into the eaves and corners which inhibits air flow?

Thanks DoctorAllcome and Wowfudge, I’ll check out the loft and get someone in who can make an assessment if I’m not sure

We had this - you could see the lines of the loft rafters forming in the mould. In our case i think it was the loft insulation which had been packed too tight to the edges.

A photo would be useful. but the first thing you need is an extractor that works. Many are underpowered.

Is yours in the ceiling or the wall? How high above the floor? Where does it vent to? When is it turned on (and off)?

we have some mould in the bathroom so following along.

I think we need a new extractor, what's the best position?

above the shower, where the steam is greatest

on the ceiling, because water vapour is lighter than air, so rises

furthest from the door, because replacement dry air will be drawn into the bathroom through the gap under the door. The hot wet air will stratify above it.

How high is the ceiling in your bathroom? If the fan is mounted less than 2250mm above the floor (try to avoid that) extra electrical safety rules apply.

If you can put the fan in the loft above the ceiling, with a duct going through the wall (it must never vent steam into the loft space), you can get some very fine extractors.

If you have to make a new hole in the wall, make it to fit a 150mm duct (common bathroom fans are 100mm but it is easier to make a bigger fan that is quiet and powerful). 150mm diameter hole is more than twice as big as 100mm (yes it is)

thank you @PigletJohn

The problem isn't defective plaster board it's just pattern staining from the wood which is not as insulating as the actual insulation.
You could reconfigure the insulation above if there's space, improve the heating and ventilation, or overboard the ceiling with insulation.

I hadn’t considered that, thanks

I think that’s the issue it’s in the ceiling over the bath, far away from the shower that gets used at least 3 times a day

I’ll have a look. Thanks

if you have access above the ceiling, this can be improved fairly easily.

Having a grill above the shower will improve efficiency, but very likely your existing fan is not powerful enough. If there is a duct in the loft, a more powerful one will probably fit in to replace the old. Any photos will be helpful.

Does the fan automatically come on with the light switch? Even a not-very-powerful fan can be left running for long periods to reduce humidity. Modern fans are very cheap to run (between 50 and 200 hours on 15p worth of electricity, depending on power)

Thanks, Piglet John. The extractor fan comes on with the light, so we’ll try running it for longer periods and open the window more often. I can’t send photo because I only just registered with mumsnet recently and apparently I have to wait a set period of time. But thanks 🙂