Threshold for Mould on Timber

[Gaf]

Attached photos of timber ceiling battens that were installed.

 

Are the dark mould patches just something you have to live with when using timber or would this be too much? 

 

Plasterboard to be screwed to these, then skimmed.

[Gaf]

[Mr Punter]

Unless you select the battens yourself, this is about standard.  Often massive knots, twisted, bent, soaking wet.  Sometimes I get a pack delivered and they are all perfect.

[Gaf]

So likely most houses have battens like that? And cause no issues from a mould growing perspective?

[Kelvin]

We never had any mould but we did have loads that were knotted and bent. However given you have to cut some of them I used the worst ones for the cuts. 

[Gaf]

On 20/08/2025 at 14:11, Mr Punter said:

Unless you select the battens yourself, this is about standard.  Often massive knots, twisted, bent, soaking wet.  Sometimes I get a pack delivered and they are all perfect.

 

On 20/08/2025 at 15:30, Kelvin said:

We never had any mould but we did have loads that were knotted and bent. However given you have to cut some of them I used the worst ones for the cuts. 

 

Yeah I’m torn on this. Dropped in to four local timber suppliers and they all initially thought I was showing them photos of battens in a really old house. When I said it was a new build there was an unequivocal ‘get them ripped out and replaced’ and there should be no mould on newly installed interior timber.

[SimonD]

It's not necessarily mould. You can find that new timber gets black marks after it gets wet as bacteria like to devour the sugars in the wood. Once the sugars are gone, and/or moisture dissappears there will be no further problems and you'll probably find the black softens to grey. 

[SteamyTea]

19 minutes ago, SimonD said:

Once the sugars are gone

We had a discussion about this happening on plywood.

Too tired to look it up now.

[Iceverge]

Give the battens a dig with something pointy and see if the timber is gone soft. 

 

If it isn't then it's just surface mould and I wouldn't worry about it. Mould is easy to combat. Just control humidity (heat and ventilation) to ensure the material in question is never colder than the dew point. 

 

Inside your warm and dry house it won't stand a chance. If you're worried about the surface mould you could sand it off or wash it with bleach but I really wouldn't bother. 

 

 

 

 

[SimonD]

12 hours ago, SteamyTea said:

We had a discussion about this happening on plywood.

Too tired to look it up now.

 

Yes, it was some time ago. It also commonly happens on cladding - I went into a panic years ago because my lovely new cedar cladding started developing black splotches on the north face of the house. Now it's a uniform silver. On the south side, the same process is happening but much more slowly.