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Would sealed air vents on old concrete house cause mould?

Just Starting Out

Would sealed air vents on old concrete house cause mould?


I bought an old house to fix up a couple years ago. It had old vents on the walls in the upper corners. My girlfriend hates cold and wanted them sealed up so I filled them with gap filler and painted over them. 

During winter we have quite bad condensation on the outside walls which can lead to mould. I'm very vigilant on any mould and get rid of it whenever it appears. Will opening these vents again get rid of this condensation or is it something that can be controlled through other means? I have a couple small dehumidifiers which help a bit. 

Amassing an Audience

Re: Would sealed air vents on old concrete house cause mould?

Hi @Jamie091,

Welcome to Bunnings Workshop, it's great to have you along!

Please do not seal up them vents, they are there to ventilate the walls themselves and they should have no effect on the actual temperature/moisture level inside the house itself.

Sealing them up will makes things twice as worse as these vents help the building to breathe.

What sort of heating are you using inside the place at the moment?

My advice would be to get a fan unit installed in your roof void that will blow warm air down into the house and mitigate the condensation, I did this

in my place and it worked wonders after having mould on a lot of the walls on the south side of the house when I first moved in here.


I hope this helps, if you need any further advice, be sure to let us know with a post below.


Cheers, Mike T.


Re: Would sealed air vents on old concrete house cause mould?

Thank you Mike


We've already sealed them up. We had an open fireplace last year which kept the moisture level down a bit but I've tried unsuccessfully to install a fireplace insert and having trouble to get a professional to come look at it as we are in a remote town. Currently just using electric heaters. 


There are no gaps between the walls. They are solid concrete slats with a thin layer of what I think is gyprock over them. The vents lead directly from inside to outside with nothing between them. 


As for the condensation problem - I can't see any way to help with insulation for the exterior walls as there is nowhere to put it unless I put up new dry wall. I can put insulation in the ceiling. I've looked into thermal paints but they don't seem to do much if they work at all. Planning to repaint the walls with anti-mould additive so it could at least help with mould a bit. We're buying new curtains to cover the windows. Looking in to buying a better dehumidifer but don't want to spend the money unless I know it works well and is energy efficient as with our heating the electric bill is through the roof. And other than that it's trying to get this fireplace working asap to warm the walls up a bit. 

Bunnings Team Member
Bunnings Team Member

Re: Would sealed air vents on old concrete house cause mould?

Hello @Jamie091 


Allow me to welcome you as well to the Bunnings Workshop community. It's wonderful to have you join us, and thanks for sharing your question about the sealed air vents.


I'm afraid the only way to prevent condensation from getting trapped inside the house aside from using a dehumidifier is to provide ventilation. 


I understand that you're not keen on adding more ventilation in the house, but I propose having a look at the following vents as a possible option.


Vents with closing features:



In order to get even better air circulation, you can add and link an inline fan to the vents and pump out the air. The best part is that once you've vented the house you can close the vent openings to prevent the cold air from getting in.


In regards to adding insulation to you brick walls, installing a timber batten frame would be the way to hold the insulation on your wall.


If you have any other questions we can help with, please let us know.




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