plaster on walls , could it exacerbate condensation?

[aprilsweetheartrose]

Well the question is in the title really.

I have a 1950's bungalow in deepest darkest Cornwall ( it rains a lot and is damp). I have been battling condensation in my kitchen for nearly 20 years. I have changed windows, painted with mould paint and waterproof paint and done all kinds of shifting round. I have even tried not breathing in there!

However, I have observed , since I removed the old pantry and the room larger ( it was 12ft x 12ft, now 12ft x15 ft) that on the walls where the pantry was removed and OH plastered the sections up, it doesnt get black mould. There are two distinct strips on the walls that are clear of any mould and seem to not suffer condensation.

Could the problem I have be related to they type of plaster they did the walls with back in the 1950's?

Any solutions to that, other than having all the plaster knocked off and re done ( in the extreme I would consider it, I am sick of walls dripping with condensation when I cook or especially on weekends like this last one- rain, rain and rain).

Thanks for all sensible answers. I wont be replying to trolls.

[harry]

Condensation is best tackled at source. Cooker hood (extracting air to outside) With provision for air to come in and replace extracted air. Also extract fan in bathroom. Especially if you have a shower.

Are your exterior walls insulated?

[tabbypurr]

there are several ways to reduce RH & condensation.

1. dehumidifier
2. look at your cooking methods. Some people use way more power than needed, resulting in lots of unnecessary steam.
3. Insulation on the wall under the plaster.
4. Removing debris or plants blocking wind & sun outside.
5. Sometimes faulty rainwater goods adds to the problem. etc etc

NT

[aprilsweetheartrose]

Yes, I have done all the insulation in the hope it would work but , if anything, its made things worse.

[aprilsweetheartrose]

Done all of that. Hd a dehumidifier on yesterday when cooking main meal. I am not generally a big cook, so I do far less cooking than many people. I also put lids on the saucepans etc.

There comes a point when the problem is such it needs to be sorted rather than my being told not to breathe ( which seems to be the problem now.

I asked OH for a PIV as they say this cures all but he is against it and says it wont work, so I am still lookong for anything else I can do. I am getting asthma from the black mould now and it is beginning to spread out of the kitchen and moving though the house.

Its becoming a stupid situation. Before all the re modelling ( when we had old steep windows, the problem didnt seem to exist except in one corner on the back wall. Now its the whole wall and its moving across the ceiling and down other walls. In fact, if I didnt spray it with mould killer every week, the whole kitchen would be black with mould by now.

[aprilsweetheartrose]

Funnily, I dont have a problem in the bathroom - and yes, I have a shower. I did have a problem there 20 years ago. I got rid of the carpet, removed the shower screen and put in a bath with a shower curtain and suddenly the mould and condensation went. ( and there isnt even an extractor fan in there either. I just open a window for an hour after the shower is used.)

Not so with the kitchen I am afraid. Windows, doors open, dehumidifiers running (although if I leave the dehumidifier on for around six hours it will reduce the condensation - but it returns overnight when I switch it off.... OH says it costs too much).

The back wall ( North North East facing exterior on two sides) is the worst.

[Chris Hogg]

In the late 1970's, the bungalow next door to my mother was modernised by a couple of cowboys while the new owner was abroad for several months. The cowboys used beach sand when rendering the walls. The sand was salty, and the owner had to have it all stripped off and re-done because it held the damp.

Not exactly the same as your problem, but similar. Also in Cornwall but further west from you.

[John Rumm]

You may find that the new plaster is not yet as saturated as the old, and so is a little more thermally insulating. Damp plaster conducts heat better than dry, so it becomes a vicious cycle.

I have also found that once a finish has supported mound once, its more likely to reform on the same surface.

What is a PIV?

That's not an uncommon experience, when you shift to more air tight windows condensation can increase. Also the condensation will tend to form fastest on the coldest surfaces - so old single glazed windows will attract far more than modern DG windows. However this can mean that when you replace old windows you now get more condensation on what are now the "new" coldest surfaces, made worse by the reduced ventilation.

There are only two ways of reducing condensation really - reducing the moisture content of the air, and increasing the temperature of the surfaces above the dew point for the RH of the air in the room.

(this assumes that condensation is the only source of damp).

When you say the walls are insulated, how are they insulated? (i.e. internal, external, cavity fill etc).

Are they any other possible sources of damp ingress (e.g. bridging from outside, or leaking gutters / downpipes etc).

What is the external wall construction? (e.g. solid brick, brick with cavity etc)

[tabbypurr]

If it's that bad with a dehumidifier on all the time then you must have a leak, either from plumbing or rainwater goods.

NT

[Harry Bloomfield]

[e-mail] wrote on 03/12/2018 :

Very unlikely. Condensation occurs on walls, because they are cooler than the air temperature, but exacerbated by too much moisture (high humidity) in the air.

So there will probably be a lack of insulation problem, in/on the wall where it is condensing. Might that wall be an uninsulated section, or a

9" none cavity wall? Also look for any other reasons why that wall might be cooler.

Moisture in a home, needs to be extracted at source - bathroom extract fan, cooker hood extracting to the outside, including carefully controlled ways for air to get in to replace extracted. A dehumidifier might also help, where there is no other way.

[George Miles]

There are humidity controlled fans available which work when there is too much water in the internal air.

condensation happens on the coldest surface

Get an infra red temperature gun to check temperatures in walls and ceiling, i bet the area with mould is colder.

It takes time for the mould to clear up

A cheap > Well the question is in the title really.

[GB]

I strongly suggest that the dehumidifier is left on 24/7. Also, which make/model is it? It may not be powerful enough.

Where do you dry your laundry? If it rains a lot, it's probably indoors. All that water in the laundry has to go into the air. It then condenses on the coldest walls and causes dampness.

Typically, when it comes out of the machine, my laundry weighs about

5-10Kgs more than the dry laundry when it goes into the machine. That's a bucket of water that gets evaporated into the air, and quite possibly in your case it condenses on the walls.

To combat that, when drying laundry, you need a window open, decent heater on, and preferably a dehumidifier as well.

You may have porous walls or defective roof/gutters, but it's best to combat the obvious sources of moisture first.

[aprilsweetheartrose]

no, its not that bad all the time. Its mainly when we have cold and damp weather in winter. Today is dry and the wall has cleared up completely. You wouldn't even know.

I have checked all the guttering and roof. They are sound.

It is just condensation.

[tabbypurr]

that much condensation with a dehumidifer means 1 of 4 things:

1. it's not being left on
2. it's broken
3. it's a long way away
4. you're trolling.

NT

[tabbypurr]

I suppose it might be one of those mini peltier jobs, which are almost useless.

oh lord. Doing all 3 is entirely useless.

walls are normally porous, it's not a problem.

NT

[GB]

You need fresh air and heat. I agree the dehumidifier is pretty pointless, but that should stay on 24/7 IMHO and it's daft to turn it off when drying laundry.

We have roughly 18-24" overhanging eaves, so not much water hits the walls.

[tabbypurr]

If you apply fresh air & heat, the heat gos out the window uselessly. So that's a pointless combination. Fresh air works to a limited extent, but only gets things dry if outdoors is also dry - and it's not in winter when damp is worst. Heat alone has some effect, but again not great. It's enough in a well designed house in sound condition, whether that's so in the OP's case is open to question from what's been described. The most effective of the 3 by a long way is dehumidification. Obviously the dehumidifier has to work, boxes of chemicals & peltiers don't qualify as useful dehumidifiers for 99% of cases.

NT

[George Miles]

perhaps when cooking is done the kitchen door is closed and the room cools down to beneath the dew point so water condenses on the coldest surface - if you insulate one surface it will condense on the next coldest.

[g]

[GB]

I don't agree, I'm afraid. Well, okay, I agree that the dehumidifier works and is energy efficient.

Warm air can hold more moisture than cold air. (See for example

)

So, you can take cold air from outside with 100% rel hum, heat it, and its rel hum drops. You can see from the graph that air at 0C with 100% rel hum drops to about 50% rel hum when heated to 20C. You can then evaporate the moisture in your laundry into it, and vent it outside.

There's no point heating the house without adding ventilation. That would just dry the laundry and trap all the moisture inside the house, ready to condense on the cold surfaces. You need to vent the moist air outside.

I hope that makes sense. If not, this could be hard work!

[tabbypurr]

a good start

yes

yes. Then RH goes up again as more damp evaporates into the air so indoor air is above outdoor air in water vapour content while being lower in RH in winter. That's why heated houses are lower RH indoors than outside. The normal trickle of air exchange between high vapour low RH indoor air & low vapour high RH outdoor winter air has a drying effect, countering our adding water vapour by breathing, cooking, bathing etc.

you can, though it's a wasteful thing to do

no, sorry. All houses have ventilation already, whether incidental (in most cases) or deliberate. If they didn't we'd suffocate. That inbuilt ventilation is normally sufficient to keep a house dry if heated.

But at the end of the day either increasing heating or adding more heat AND more ventilation are both wasteful options. They are also nowhere near as effective as a dehumidifier.

NT