Cold wall mould

Danny30

Hi, I have an external bay window wall in my daughters bedroom that is very cold and has had some mould growth on the walls recently. There is strangely no window sill and largish gaps in the wall under the window allowing cold air in. I intend to fill these up. 
Can anyone advise me if this would help to stop the mould growth? Also would I need to use expanding foam to fill in the gaps before filling them?

FreeBear

Some wider views of the bay would help. Certainly, sealing any gaps will help.

Depending on the age of the property, many bay areas are a lightweight construction lacking any insulation.  It may be that yours is a studwork wall, clad externally with brick, tile, or render and just a lath & plaster (or possibly plasterboard). If so, removing the plaster internally and filling the void with insulation (Celotex/Kingspan type boards) would pay dividends - Reducing heat loss, cutting out the draughts, and a much warmer room. Downside, it will cause a lot of mess and the room would need redecorating. Needn't be hugely expensive though. If you can do the work yourself, maybe £100 for materials.

Emmia

Once you've sealed the gaps, you can use bleach (or a mould/mildew remover like the cif spray one) to kill/remove the mould before decorating again.

If using a spray, I'd advise spraying onto a dish sponge then wiping on the wall being treated as an effective way of doing this and avoiding damage elsewhere... You might also want to think about paints with mould inhibitors in them too.

I'd bin the sponge afterwards too.

Danny30

Thank you for the replies. I am going to try and fill the wall and apply bleach first and see if it improves. I don't fancy knocking the wall through for the now (hollow brick wall not cavity) due to the hassle involved. 

Danny30

Quick update : I have filled all the gaps in the wall and have noticed so far no wet or condensation on wall but still early days. There is a lot of condensation showing on lower part of windows. I did notice when filling gaps that I could see a spot or two of daylight from external wall of bay window so could that be allowing  cold air to come in through gap and causing the condensation on the windows? 

TheEssexlad

You could line the external walls with a thermal lining paper https://coveryourwall.co.uk/collections/thermal-room-insulation-liners  ,and then paint with an anti mould paint , you don't really want to be breathing in the mould spores , if the rest of the house suffers as well , a dehumidifier would really help , 

Murmansk

Water tends to condense on a cold surface so you need to reduce the cold surface and/or reduce the amount of moisture in the air. Sources of moisture in the air are cooking, drying clothes indoors etc. Maybe try a dehumidifier - I used to get mould in my third bedroom where I dried clothes and a dehumidifier solved it