Bathroom ceiling.

[artie]

There's a bit of mould formed on the bathroom ceiling.
Previously it was a bedroom with just a painted ceiling.
The extractor fan appears to me to be a little under powered but the ducting is sealed ok, so it's either live with it or replace it.
I would like to get rid of the mould completely so I'm thinking about an inch or two of insulation and then some kind of pvc type covering and if necessary a new fan.
I want to cure the problem for good.

Fire away.

Ps. The house was built in '30s but the loft is amply insulated as per 2020 specs.

 

[Robin Whitfield]

But is the loft actually well insulated where the mould has formed? It's pretty common for insulation to not be very well fitted (or as deep) close to external walls where the roof pitch makes installation difficult, and that top outside corner tends to be the coldest part of the room.

I have admittedly considered very similar for my bathroom though due to those difficulties although just a standard skimmed and painted PB/wallboard ceiling on the insulation. With only an inch or two of insulation presumably the whole lot could just be held up with some long PB screws all the way through into the timbers above.

 

[NikNak]

So its a biggish room then if it used to be a bedroom.?
Has the problem only started since converting from a bedroom to a bathroom.?
Whereabouts in on the ceiling is the problem... i.e. is it in a corner, over the bath/shower, roughly evenly spread.?
Before embarking on any 'cures' (you may already be doing this...) but I'd say open the window after having a steamy bath/shower as well as having the extractor on, maybe for half an hour or more depending on how 'steamy' the room is, dont just rely on the extractor. And if possible increase the time that the extractor stays on after switching it off.
We have an ensuite shower with an extractor and window, and a bathroom with just a window. Neither room suffer from damp/mould as the windows are always opened after a shower or bath for at least half an hour... summer or winter.

 

[sunnybob]

You can now buy humidity activated extraction fans. Fully automatic. And about the same price as old fashioned ones.
But the main reason for damp and mould is the room is too cold. is there a radiator or towel rail? turn it up. If the towel rail is electric, leave it on longer. 22c is the dew point of moisture in the air. Below that and you will get mould on the ceiling and walls.

 

[Robin Whitfield]

22c is the dew point of moisture in the air.

You're missing a variable or two there.

 

[artie]

All good points.
Robin Whitfield
The mould is mostly above the shower but spreading.

NikNak
It's roughly 9 ft by 9 ft, it was the smallest room in the house apart from the previous bathroom.

There didn't appear to be any signs of mould before it was converted, but I did it before I even moved in so..

Yes it might be an idea to try to ventilate better, must remember.

sunnybob
A hunidity activated fan sounds like a plan.

There is a large towel rail powered by the CH, but 22 deg sounds very high I usually only have the living room at 20 - 21 in the evenings.

 

[Robin Whitfield]

There is a large towel rail powered by the CH, but 22 deg sounds very high I usually only have the living room at 20 - 21 in the evenings.

If your ventilation isn't good enough and the room's 22C you'd still have damp issues. Having a bathroom 17-20C is no issue with adequate ventilation. As the temperature of the room goes up, as does the capacity for the air to hold moisture, but it'll happily still condense on the walls/ceilings.

Being built in the 30s it's unlikely that there's not enough incoming air into the bathroom but if you've had renovations and windows without trickle vents then that could be part of the issue. Most bathroom extractors do not have a very a very high static pressure capacity so if incoming airflow is restricted (tight fitting door and no/small window vents) then they can end up not actually doing very much despite spinning around just fine.

 

[sunnybob]

Allowing for the fact we are talking everyday approximations, not scientific theoretical calculations, if the coldest part of the room is 22c or more, in the UK, there wont be any condensation or mould on the walls. I've proven that on many occasions.
A bathroom is a worst case scenario, because nobody keeps the bathroom at comfortable room temps, at the same time as it gets more humidity than anywhere else.

A balance has to be struck. Vent fans are a must (open windows dont actively remove moisture, they just allow cold air in to make matters worse). Most central heating systems use the bathroom radiator / towel rail as the always open point, which helps, but if you set the downstairs thermostat low, then the boiler shuts down before the unused bathroom can get warm.
Do any of you remember the old bathroom wall heaters? 500 watts, you never got condensation with one of those.

 

[Spectric]

Hi all

The best solution for condensation is drafts, ie airflow. Modern overly heated homes that are sealed will be more prone to these problems, all warm air will contain moisture, the higher the temperature the more it can hold and when it contacts a cold surface its temperature falls and the water condenses out because it can no longer suspend that amount of water at that temperature. The biggest sources of water vapour are people(Living) and damp washing. So your ceiling is to cold and needs further insulation, or you could use a very big extractor fan and remove all the heat. I have no issues and no extractor fan but lots of insulation. Walls where the plasterboard has been put up using dot and dab can also be prone to dampness, especially if they are non cavity walls.

 

[Robin Whitfield]

Making all parts of your bathroom 22C is unrealistic and unnecessary and I'd guess that at least 95% of the UK don't have their bathrooms (or any part of their house) that warm. I have an extractor in my bathroom but it's never used and never warmer than about 17-19C. It doesn't even have a radiator in it at this moment. The trickle vent in the window combined with the draughtiness of the house is sufficient to keep things under control. More people having daily showers would likely necessitate that the fan be used though.

MVHR is the ideal solution but it's a difficult retrofit in our typically brick, concrete, and stone built UK houses and still is very rarely installed in new builds.
There's enough of an issue getting a decent level of insulation in new builds let alone anything fancier.

 

[Woody2Shoes]

Making all parts of your bathroom 22C is unrealistic and unnecessary and I'd guess that at least 95% of the UK don't have their bathrooms (or any part of their house) that warm. I have an extractor in my bathroom but it's never used and never warmer than about 17-19C. It doesn't even have a radiator in it at this moment. The trickle vent in the window combined with the draughtiness of the house is sufficient to keep things under control. More people having daily showers would likely necessitate that the fan be used though.

MVHR is the ideal solution but it's a difficult retrofit in our typically brick, concrete, and stone built UK houses and still is very rarely installed in new builds.
There's enough of an issue getting a decent level of insulation in new builds let alone anything fancier.

Single room mvhr units are available and pretty much as easy to install as a conventional fan unit

 

[Jackbequick]

I appreciate you can do your own research, just thought to give some URL's with a variety of muse-material. Before that, in my opinion ceiling fans are a waste of time or worse unless there is airflow in the cavity into which they usually expel air. They otherwise and maybe 'even so' deposit moisture onto insulation or inner (unpainted) ceiling. A warm heater fan 'blower' with window/s ajar (safely placed and fixed) is better.Just having a fan is not per-se a solution, it could in fact worsen the mould situation.

Today's common issue with rabbit-warren living (said disingenuously to be better for us than a house and land) is bathroom without window...which then requires a fan on regulations. Sadly regulation does not demand ventilation which is geared to reducing mould, nor does anyone seem to care...'got a fan?...yeah...ok, tick box

Wall heaters such as gas left running particularly, can see moisture deposited on walls and ceiling during operation. One has to get airflow to outside to help reduce spores and activity. I suggest a heater blower which is 'on' just long enough to move warm air and condensation 'outside' and then enable ambient air flow.

Then one must pro-'actively' arrest mould production and infestation...which means more bathroom hygeine and care than one might imagine. hat means cleaning, dry towels and awareness of what steam from our bodies carries.

Some useful information (food for thought and expanding thinking) ...and I know there are many sites...some which can correctly spell 'mould'.

The first is very worthwhile in "getting the mind right" as was quietly put to'Cool hand Luke' by the prison boss with the aid of a cosh/blackjack. This one has pictures which I think useful.

https://efficiencymatrix.com/stopping-bathroom-mould/
https://www.thespruce.com/tricks-keep-bathroom-mold-free-326859
https://aerindustries.com/blog/2018/11/20/how-to-stop-mold-growth/

 

[Robin Whitfield]

Single room mvhr units are available and pretty much as easy to install as a conventional fan unit

Sadly the small in wall units tend to not be so effective as rather than transferring heat to the incoming air directly they transfer it to a solid material to then be recovered by the incoming air when the flow is reversed. There's also no real movement of air through a house with them aside from the negative and then positive pressure they produce when operating. Unless your house is very well sealed they're pulling in outside air and pushing heat back out somewhere else as they operate.
When you're having a shower they tend to have an override function that just runs as a fan.

The larger wall units are better as they're at least balanced with their flow and have direct heat transfer, but they still only really work for a single room.

Any better than that and you have the usual ducting issues.

 

[Robin Whitfield]

Before that, in my opinion ceiling fans are a waste of time or worse unless there is airflow in the cavity into which they usually expel air. They otherwise and maybe 'even so' deposit moisture onto insulation or inner (unpainted) ceiling.

UK Building Regulations should ensure that never happens but you get plenty of dodgy builders prepared to vent fans into a ceiling.

None of them are designed to be used like that. They should always duct to outside.

 

[artie]

Fantastic input guys, I've spent the whole evening researching Humidistatically controlled fans, to then come back here and find I have to go and do the same now for single room mvhr units, as well as catch up on the other points put forward.

Any such thing as a ceiling mounted mvhr unit? As the bathroom it tiled top to bottom.

 

[gregmcateer]

We're landlords and a couple of bathrooms had similar problems. We appear to have solved them by installing humidistat 'silent run' fans, which are almost silent and can be boosted when user in the room having a shower.
I'm no ventilation engineer, so can't tell you details of why it seems OK now.

 

[Woody2Shoes]

Sadly the small in wall units tend to not be so effective as rather than transferring heat to the incoming air directly they transfer it to a solid material to then be recovered by the incoming air when the flow is reversed. There's also no real movement of air through a house with them aside from the negative and then positive pressure they produce when operating. Unless your house is very well sealed they're pulling in outside air and pushing heat back out somewhere else as they operate.
When you're having a shower they tend to have an override function that just runs as a fan.

The larger wall units are better as they're at least balanced with their flow and have direct heat transfer, but they still only really work for a single room.

Any better than that and you have the usual ducting issues.

The ones I have work just fine - they have what is effectively a "bunch of plastic drinking straws" as the heat exchanger. The intention is not to move air around the house, it is to swap warm damp air in the one room with warm less damp air originating outside (as opposed to cold less damp air without the heat exchanger). Since the bathroom is a major source of warm damp air, the fact that it's a single-room (and easily retrofittable) solution is not a problem. Cheers, W2S

 

[OldWood]

Insulation , insulation, insulation. The reason for the mould is condensation on the walls/ceiling because the walls are so much cooler than than rest of the space. Yes extraction is important, but I had mould through out this house originally, (18th century cottage nr. Edinburgh with an 1920's update), and it wasn't until I stripped off the lathe and plaster and insulated between the stone and plasterboard that it went, with of course plenty of rood insulation.

 

[NikNak]

Like gregmcateer we used to be landlords (sold last place back in the summer) and the times we used to get calls saying "theres mould appearing in xyz room..." We'd go and have a look and they were using tumble dryers with no venting, drying clothes on top of radiators, not opening windows after a shower/bath let alone not even thinking about switching the darned extractor on... "we didn't like the noise it was making so we turned it off..."

Presuming your walls adjacent to the 'water' are tiled i.e. shower cubicle and bath sides... if so we find if you have a handy squeegee/rubber bladed thingy then if you remove/wipe away most of the water on them before you get out of the shower/leave the bathroom, then you've eliminated 95% of the water anyway. Plus it has the added benefit of eliminating water staining and mould growth in/on the mastic too.

Ventilate ventilate ventilate..... then close the window....

 

[artie]

Reading through the links provided by jackbequick I see it is recommended to change the air in a bathroom 8 times per hour.
Mine is 688 sq ft, so I need a fan capable of shifting 5500 sq ft per hour, But even fans costing in excess of £100 are rarted at 20% or less of that.
Or have I put a decimal point in the wrong place?