Mould on 1 Wall What Can I Stick Over It Before Plastering?

[SquirrelMadness]

Back of the terraced house external wall has a tendency to attract mould. The mould is present in bottom corners, inside the cupboard and around the window frame.

Over the years tried various bleaches and mould removers, none worked. Kept windows opened overnight. There is no other vent.

I want to rip off the skirting and shelves and replaster the wall because it's ugly and has a lot of imperfections outside of the mould issue.

I noticed bathroom on same side doesn't have mould (because the tiles duh). So I'm thinking of putting something on the wall before I plaster it.

Anyone got an idea of what I can stick on? Don't want it too thick but can go to around 12mm.

I was thinking something like this:

EDIT PICS:

Thanks.

 

[kindai]

Can you show us the problem area (inside and outside). If theres persistant mould that is coming back, you need to look into the cause of it.

 

[Deleted User 298457]

How old is the house?

 

[SquirrelMadness]

Can you show us the problem area (inside and outside). If theres persistant mould that is coming back, you need to look into the cause of it.

Edited with pics. House is 1940s.

 

[kindai]

Edited with pics. House is 1940s.

Is that a conservatory roof direct up against the render?

It looks like you have a damp problem, either something from the roof/guttering of the top corner of the room or something with how those polycarb sheets are resting against the render.

You could also try a PIV unit. But realistically you need to find the cause of the damp first as covering it up wont really help.

 

[Deleted User 298457]

Pics of conservatory roof/lean to? It should be flashed on otherwise it is just holding water up against the solid brick wall and leaching through. Nothing you do interior will stop that.

Also check/inspect guttering for blockages.

 

[SquirrelMadness]

The mould issue predates the lean-to build (2016).

The gutter was last cleaned around 2021 I will check again but doubt that's the issue.

The wall is not insulated at all.

I just removed the L brackets from the cupboard and there is no damp underneath them. Doesn't this say the damp is coming from within the room rather than externally?

 

[SquirrelMadness]

The wall gets a lot of condensation when the house is heated during winter.

Also those wet marks on the wall are from bleaching/cleaning the mould with a sponge.

 

[Buffman]

Get trickle vents in your windows!

The issue is condensation going to the coldest point and turning to water on that wall. The fact its an unventilated area doesn't help.

Id much sooner get trickle vents than a piv unit (having previously had PIV units)

You could also insulate the walls such that moisture will instead condense on the next coldest point, the windows.

 

[LuckyBenski]

You could also insulate the walls such that moisture will instead condense on the next coldest point, the windows

Agree with this TBH. Insulation will address the condensation which seems a relatively direct approach if you're confident it's not a leak or similar.

PIR board?

 

[Rroff]

Not really supposed to be used for this but I find Green Gone by far the most effective in these kind of situations - however if mould removers aren't working that is probably due to persistent presence of damp and possibly not just from condensation.

Cavity wall insulation was a game changer for us when it came to mould in one room which has a large north facing wall.

(Also looks like Green Gone wouldn't go amiss on the lean-to roof).

 

[SquirrelMadness]

Mould removers do "work" it's just that it has to be done every couple years and cupboards are hard to reach areas.

The walls can't be insulated unless externally. No-fines concrete. I can insulate internally but has to be around 20mm insulation which probably isn't worth it?

Could do trickle vents TBH... drill holes in top of windows. Would this work even with blinds over the top?

I'm starting to think the best way is to get a plug socket into maybe the cupboard and have a 20L dehumidifier running constantly.

 

[SoliD]

Agree with this TBH. Insulation will address the condensation which seems a relatively direct approach if you're confident it's not a leak or similar.

PIR board?

Absoutely this, made huge change in my house by insulating all of upstairs with 50mm PIR added internally. Could chuck some insulated plasterboard in this space with just 12mm of PIR in you can't lose a lot of space and this will likely help massively reduce or eliminate the issue.

 

[fastwunz]

Oh! It’s a wimpey no-fines house! No wonder you have issues lol - max ventilation is needed

 

[SquirrelMadness]

Is there an insulation that can be directly plastered? I don't think I need the plasterboard just some type of insulation panel I can adhesive to the wall and plaster over.

 

[LuckyBenski]

PIR backed plasterboard like this

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(Haven't checked if those are good prices)

 

[Sin_Chase]

You really need to do this properly. You cant just dot and dab PIR onto a problem wall and plaster it.

You can make a condensate issue WORSE on your original internal walls with insulation as you make them even colder.

You need to consider ventillation, vapour barriers etc. A common method is to batten out with a vapour barrier and then board.

We solved a huge amount of condensate and mould issues in our old solid wall 1930s house with a PIV install (Positive Input Ventilation).

We got a NuAir Drimaster in the loft with a central upstairs hallway vent location. Installed it myself. You may wish to consider this.

 

[gazref]

Can you not just treat the area/clean and paint it with Zinser 123?

 

[SquirrelMadness]

PIR backed plasterboard like this

I mean something like tile backer board but it's insulation and instead of tiling you plaster it (so no plasterboard).

You can make a condensate issue WORSE on your original internal walls with insulation as you make them even colder.

...vapour barriers etc. A common method is to batten out with a vapour barrier and then board.

But wouldn't that only apply with damp coming through the walls not moisture just landing on cold walls and turning into mould?

Can you not just treat the area/clean and paint it with Zinser 123?

Been doing that for the last 10 years minus the Zinser paint.

 

[gingergundog]

You really need to do this properly. You cant just dot and dab PIR onto a problem wall and plaster it.

You can make a condensate issue WORSE on your original internal walls with insulation as you make them even colder.

You need to consider ventillation, vapour barriers etc. A common method is to batten out with a vapour barrier and then board.

We solved a huge amount of condensate and mould issues in our old solid wall 1930s house with a PIV install (Positive Input Ventilation).

We got a NuAir Drimaster in the loft with a central upstairs hallway vent location. Installed it myself. You may wish to consider this.

Agree on the drimaster, amazing pretty much removed our condensation within a couple of weeks.

Re the insulating solid walls, I've done it and it was a success(insulated plasterboard direct on solid wall). I think there is a bit of a misunderstanding regarding making the walls cold, if you reduce and slow down the amount of moisture passing through the fabric of the building the temp of wall matters less and id expect any moisture to dry from inside out.