Mildew all over plywood walls

[Omnibuswoman]

46 minutes ago, SteamyTea said:

Just need to find an offcut of clean ply, char one side and leave in a shed.

good idea. We have a blowtorch here and some ply that has stayed unaffected. I’ll do a controlled test - one Japanese charred and one not. See what happens! 
 

However, for my workshop, I don’t favour the “had a fire” look, so will be trying the zissner paint first. 

[SteamyTea]

10 minutes ago, Omnibuswoman said:

However, for my workshop, I don’t favour the “had a fire” look, so will be trying the zissner paint first. 

Call it a Finnish Shed.

The idea is to then sand, prime and paint after the burning.

 

[riboid]

On 27/10/2021 at 09:05, SteamyTea said:

To me, Solum is a single type of soil, which may, or may not be in layers with other soil types.

So may be missing something here.

 

But basically, once the spores are in your building, and they will be, they will find a niche and multiply.

Yes, mines is certainly missing the coal tar, basically gone in a lot of places. Require a major clean up and then repair of the solum.  Another major project...

[Ferdinand]

4 hours ago, Omnibuswoman said:

i bought a tin of zinsser white anti mould paint a couple of days ago, preferring it over the dulux anti mould because it had more sinister health warnings on the back ?

 

That's my technique.

 

Take a Green Party person along, and buy the one that causes the loudest shriek 

[Dave Jones]

this is a really good example of why many warm roofs fail. A combination of lack of properly sealed vapour barrier and the insulation (or lack off) bringing the dew point into the building.

[markocosic]

Cut through the panels to see if it's the blue fungus. We have some cladding boards that are streaked through with blue/grey - even when cut through. They're always the lightest and barkiest ones (sapwood verging on mill ends) and no change in 6 months.

 

Black mould, white mould, and full on mushrooms after only on the wet offcuts left in a heap outside. Stack them - covering only the top of the stack NOT the sides - and it appears to stop if not die as it dries.

 

Probably not helpful for a building sorry; but for storage...

 

 

 

 

 

[DC5]

Reading this topic with interest as we are having a similar issue with exterior ply boards which were fitted to our roof a few months ago.

 

we have no windows nor doors yet and there has been a fair bit of moisture in, the south facing roof pitch is unaffected and it isn’t all boards.

 

I don’t have the option to remove as the roof is on so I’ll need to clean then treat I think. 
 

any suggested products would be appreciated.

 

many thanks. 

[Conor]

All of our ply in the basement got mildew within days. The sheets I picked up from the builders merchants the other day came pre applied with mould.... For whatever reason mildew and fungal mould love cheap softwood ply.  It'll stop growing once heating is one and humidity drops.

[MAB]

My recent experience of ply boards used in a building project.....

 

Expensive sheets of graded marine ply from a dedicated Timber yard = no problems with mould, even with the scrap off-cuts left outside!

 

Cheaper sheets of ply from a Builders merchants  = mildrew and fungal mould appeared at the slightest sign of cold or damp in the air.

Edited January 9, 2022 by MAB

[Onoff]

10 minutes ago, MAB said:

My recent experience of ply boards used in a building project.....

 

Expensive sheets of graded marine ply from a dedicated Timber yard = no problems with mould, even with the scrap off-cuts left outside!

 

Cheaper sheets of ply from a Builders merchants  = mildrew and fungal mould appeared at the slightest sign of cold or damp in the air.

 

Same here.

[DC5]

So what was the solution?

[Cpd]

27 minutes ago, DC5 said:

So what was the solution?

Use OSB…… or sarking 

[TonyT]

Spray bleach onto it?

[SteamyTea]

Has no one tried blow torching to slightly char the surface yet.

[Omnibuswoman]

On 09/01/2022 at 21:44, SteamyTea said:

Has no one tried blow torching to slightly char the surface yet.

I haven’t yet tried this, no, but will be down there in a fortnight so will give the experiment a go. 

[Omnibuswoman]

On 09/01/2022 at 21:39, TonyT said:

Spray bleach onto it?

We have washed one of the ply panels with a strong bleach solution and it did clean it up a bit. But we have left the rest for now as we had other more pressing tasks to get done. Once the workshop is complete we will wash all of the walls with bleach (we dissolved lots of tesco bleach tablets in water to make a strong solution) then will paint with anti mould paint. 

[SteamyTea]

57 minutes ago, Omnibuswoman said:

I haven’t yet tried this, no, but will be down there in a fortnight so will give the experiment a go. 

Driving up to Bucks and Down to Cornwall all the time now, quite happy to deviate to yours and set fire to it.

[ashthekid]

On 09/01/2022 at 19:05, MAB said:

My recent experience of ply boards used in a building project.....

 

Expensive sheets of graded marine ply from a dedicated Timber yard = no problems with mould, even with the scrap off-cuts left outside!

 

Cheaper sheets of ply from a Builders merchants  = mildrew and fungal mould appeared at the slightest sign of cold or damp in the air.

 

Thats very interesting. so the 12mm ply I had in my basket I should really replace with a decent OSB.

Or still a membrane layer on before putting the OSB on?

[Cpd]

1 hour ago, ashthekid said:

Thats very interesting. so the 12mm ply I had in my basket I should really replace with a decent OSB.

Or still a membrane layer on before putting the OSB on?

I would definitely say OSB rather than ply and not quite sure about membrane without knowing what you are doing. 

[ashthekid]

It's on my perimeter structural stud work. I'm basically building a new timber frame home within the walls of a 200yr old property. The old walls we are not touching and therefore due to structural engineer instructions we have created a sizeable cavity of 200-300mm. 

The layers are as follows:

- Brick wall (or cob wall is some areas)

- Cavity space of 200-300mm (of which there is a ply and fibre resined box gutter sat on top of - I'm mentioning in case it makes a difference to temps inside the cavity space)

- 2x4 structural timber with 100mm PIR insulation in between studs

- 9-12mm ply (or OSB now instead)

- 20-25mm PIR insulation (to stop any cold bridging)

- 19-25mm batten (for services)

- 12.5mm plasterboard

 

There is little to no ventilation for the cavity space.

 

Do I need a membrane layer or is the cavity big enough to stop any mould coming through?

Do I use OSB or ply?

Do I even need a OSB or play layer?

[Radian]

We built our house back in 1996-7 and used exterior grade plywood for soffits dormers and lining porch ceilings. I kept all the surplus and decent offcuts at the back of the garage and have been feeding off them for the past 25 years. Numerous Garden projects have also come out of them and all the painted and unpainted surfaces I can see today are still perfectly fine.

 

So for our recent extension works, I had no qualms about using plywood for soffits. Soon after the sheets were delivered I noticed some mildew developing so I cleaned down with dilute bleach and applied Zinsser 123 to seal all sides. Now its all fitted and finished in Zinsser satin topcoat I'm seeing the damned black spots reappearing six months on.

 

Second Middle School? WTF China???

[SimonD]

12 hours ago, ashthekid said:

There is little to no ventilation for the cavity space.

 

First thing I would question is the lack of ventilation in the cavity between existing wall and new timber frame. Who has designed this and what is their justification for this?

 

You're going to have to be very careful about detailing the inner wall and any floor/wall/ceiling junctions correctly for airtightness/vapour control.

 

12 hours ago, ashthekid said:

Do I need a membrane layer or is the cavity big enough to stop any mould coming through?

Do I use OSB or ply?

Do I even need a OSB or play layer?

 

If the cavity has no ventilation there is risk that moisture levels reach undesirable levels, which could result in mould growth. Ventilation is your friend here.

 

I don't think it matters whether you use osb or ply. It can be easy to assume from this thread that all ply is the same. It isn't. A decent quality sheathing plywood will be fine for the life of the building. The problem is that there is some real rubbish out there supplied from builders merchants that don't have a clue about the timber they're selling and people want cheap, cheap, cheap. Any timber product, including osb will deteriorated if moisture levels are too high. My suspicion re the mould in the OP is that there has been condensation on the plywood due to natural humidity fluctuations and this has fed natural sugars in the timber, plus there have been some spores from old furniture that have added to the problem. Once the moisture levels in the building settle down and the sugars in the wood have been consumed there will be no more growth.

 

If your SE has designed the TF with sheathing, then yes. But basically all timber frames need some form of racking resistance. This is supplied using either diagonal studs at required intervals within the frame, or you use plywood/osb.

 

 

 

[saveasteading]

7 hours ago, SimonD said:

there is some real rubbish out there supplied from builders merchants that don't have a clue about the timber they're selling and people want cheap, cheap, cheap

There's a thought.... a lot of our timber, and not usually the best,  comes from Russia. Not any longer!

 

I worked with a few timber merchants (building for them) and heard some bad stories about bundles of timber with rubbish and barked lengths hidden in the middle, coming from Russia and deliberately packed to conceal illegal bits.

[Onoff]

20 hours ago, Radian said:

Second Middle School? WTF China???

 

All part of the Chinese long game. Our houses made from their cheap crap wood will fall apart. We'll have to spend more on them buying tools and materials made in China! 

[SimonD]

1 hour ago, saveasteading said:

There's a thought.... a lot of our timber, and not usually the best,  comes from Russia. Not any longer!

 

I worked with a few timber merchants (building for them) and heard some bad stories about bundles of timber with rubbish and barked lengths hidden in the middle, coming from Russia and deliberately packed to conceal illegal bits.

 

I've had some cheap Chinese hardwood ply that was full of voids. Possibly okay for basic sheathing purposes, but not nice to work with. I was also at a merchants recently to buy a particular grade of ply. When I checked, the product they wanted to sell me only had 6 plys and obvious voids whereas the product I was asking for had 7 plys and much less visible voids. They even had another pallet of the 7 ply stuff but refused to open it for me and refused to accept it was a different product. So off I went and spent my money elsewhere...