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Mould spots on new coving!

Hello - can anyone advise?
I am refurbishing an empty 60 year old property, we have had a two storey extension built on the back and we have had every wall reskimmed in the property and had new coving put up in every room. This was completed about two months ago along with new central heating, new gutters, downpipes etc…
In the last few weeks mould spots have developed on all the coving of the walls that are outside walls of the old part of the property whether this is upstairs or downstairs.
I am wanting to start decorating but unsure what to do prior to paint going on? I don’t want to trap any moisture, the walls or coving does not feel damp but don’t want the mould spots to come back through or show through the emulsion - can anyone advise best course of action?
Heating is on in the property twice a day 3 hours each time…
Thanks in anticipation…
PS - I had my own kitchen painted by one of your traditional painters a couple of years ago and it still looks fantastic…

Hi, sorry your new year hasn’t got off to a great start. As an experiment, you might want to rent a dehumidifier and see how much water you collect in it. There might be more moisture in the air from the plastering than you think. Radiators don’t really act the same way as dehumidifiers, unless you are blowing heated damp air out the windows.

With mould it is generally down to the environment you might picture in a shower room without windows- a mix of cold, then warm moist air settling on cool surfaces, lack of ventilation… the outside walls would be cold. What you describe is a typical picture of how mould can appear.

From what I learnt, use a fungicidal wash per the instructions, gloves and all that good protective clothing. When it is dried, the mould will/should have been killed, and the surface ready to paint. Maybe consider a paint with a slight sheen to it, rather than dead flat matt. The more matt a surface, the more likely mould can settle and be harder to wipe off.

Zinsser Permawhite is the first name that comes to mind, an emulsion with a built-in biocide to help prevent future repeats.

In theory you can make your own mould resistant paint with an additive suitable for paint. I used a Mythic one I believe a long time ago, they aren’t around, but I’m sure the tech is fairly straightforward and there are products from other companies like Zinsser and Kair.

Nice to hear your kitchen is going strong. cheers

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Hi dexter. Just a follow up to Andy’s reply regarding the use of the de-humidifier. If you use one that has a drain (rather than a built in collector) make sure that the moisture/water is discharged outside of the working environment or into a container with a sealed lid otherwise all you are doing is pulling the de-humidified moisture round and round hence a longer time to dry the room. Hope this helps.

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Thank you very much for your advice. Noted and will be acted upon straight away.

Thanks for the tip - will make sure I organise the dehumidifier accordingly…
Kind regards