Recently reported issues with wood fibre board IWI

[Brad Oleary LDPR]

I'm not sure, I think he's just a lime plasterer

Just a lime plasterer, I’ve got feelings you know

 

[fernicarry]

Interesting. Sounds like it’s a case of understanding how each building behaves and planning appropriately.

I’m west coast of Scotland so similar conditions. I’ve had part of the internal face of the front wall exposed for a couple of winters now and it’s always been bone dry so I’m happy to proceed with IWI.

 

[Brad Oleary LDPR]

Exactly, you can’t rush these things. Keep in touch

 

[malcolm]

I was going to say that surely people notice the interior plaster is soaking wet. Though my building regs insisted I insulate a wall that had a water line 4 feet up so maybe they don't. Impermeable materials were fine in his book. I fixed the wall instead by drying to the room and haven't insulated.

I did have some experience with a thick stone wall allowing rain to fall inside. But that was kind of noticeable.

Is it possible the failures are down to people insulating walls that are wet in the first place? Or is it that the existing wall or some part of the system was not sufficiently breathable. Cement mortars or some trade using waterproof glue or adding a bit of cement in the levelling plaster? Difficult to tell from photos but did you notice anything? I'm planning a little more woodfibre so would be good to have thoughts.

 

[Kearn]

Interesting. Sounds like it’s a case of understanding how each building behaves and planning appropriately.

I’m west coast of Scotland so similar conditions. I’ve had part of the internal face of the front wall exposed for a couple of winters now and it’s always been bone dry so I’m happy to proceed with IWI.

I thought it was one of the locations where it can be quite common to actually stand off the lath and plaster to leave an evaporation cavity on the inner stone face to allow constant driven rain to evaporate…?

 

[fernicarry]

common to actually stand off the lath and plaster to leave an evaporation cavity on the inner stone face to allow constant driven rain to evaporate

Yes. That’s how it’s currently done throughout the building. Normally I advocate keeping it clear to allow ventilation top to bottom. But it’s very tempting to fill it with insulation as that can be done without disturbing cornices and joinery. Have to try something to reduce the running costs of this place.

 

[Tuffa]

I saw this post shared on a lime related FB group. From memory I believe the post stated that the boards had been installed six months previously. I noticed that the boards didn’t appear to have been plastered. Plastering the boards is a required step that appears to be needed soon after installation. E.g. Lime Green WarmShell state render within 4 weeks. Steico specifies stringent conditions for maintaining minimal moisture in Steico Internal boards, wall and environment during storage, installation and plastering; it appears to recommend immediate plastering.

Doesn’t the plaster layer provide air tightness and so act to prevent warm moist air getting to the cold wall through the boards, and so prevent condensation…?

Would be good to confirm in this thread how long the boards had been installed, and to what extent they had been plastered!

That said, maybe wood fibre just wasn’t appropriate in this case, as pointed out by original poster. Lime Green appears to provide a method for evaluating a property. Its Warm Shell Internal ‘Site Assessment Checklist’ acknowledges that location plays a part in deciding if WF can be used, e.g it states that addresses in exposure zones 3 or 4 require that a WUFI calculation is performed. According to building regs doc C, almost all of Cumbria is in exposure zones 3 or 4…

 

[fernicarry]

WUFI calculation

Thing about WUFI is that I would have absolutely no idea how to model the existing shell of this building so it would be impossible to know how much faith to put in the output.

Aren't exposure zones for guidance on new buildings with thin blockwork skins? I'm in the most exposed zone which I'm sure was recognised when this house was built and is reflected in the thickness of the stone walls. Putting external defects aside it would take some amount of weather to saturate my 2' walls to the point that water was running down the inside. Drying it out again would be no picnic either.

You may be right about the exposed WF collecting moisture from warm internal air to some extent. My money is on the adhesive used to attach it being wrong in some way creating a barrier. Given that we have one example to look at its all pretty much just speculation.

 

[a twig]

Very much on the same side of the fence as you here @fernicarry - to me this all feels like a product that does work in the right situation when correctly installed being yeehaa’d into the wrong situation / incorrectly installed and this being labelled as “bad”.

I’ve tried insulating lime plasters and for me they aren’t worth the effort for the limited return, even wood wool boards in my experience perform better than hemp plasters, and are cheaper, faster and give a better finish.

If you have thin walls and driving rain then the traditional approach is hanging tiles or slates on the walls externally - not hoping that a lime plaster will allow all the moisture to come out on the internal side and then trying to manage it internally (either through an expensive MVHR install or using traditional ventilation methods and thus somewhat defeating the point of the insulation in the first place).

Grump over

 

[fernicarry]

I've been wondering if the affected buildings were originally build for habitation or perhaps they were agricultural buildings that were built with thinner walls? Anyway we've probably picked over the bones of this one about as much as possible.

 

[Lacan07]

What would you like to know?

Apologies just catching up with all this, I've been away over the Christmas period.

So would you say this is partly an issue with locality? The properties you work on would seem to be more exposed to wetter weathers than some of us located down South. If memory serves there seemed to be a suggestion in the comments that the interface between different materials - mineral brick to organic wood fibre - may have caused the issue. I've been chatting privately with Simon T on the FB group and he favours Multipor as an alternative solution. Its certainly worth looking at, although I'm kind of gearing up toward wood fibre in the Spring.

Mineral Insulation Board – Xella Multipor - Back to Earth

Multipor mineral insulation boards are:-

www.backtoearth.co.uk

 

[Lacan07]

I don't have any experience of stone walls or excessive rain. Wet woodfibre doesn't sound like it will work or stay on the wall for long. Would that be the glue and plaster backing not being breathable enough or the stone wall not breathable enough or leaking water in.

Mine is screwed on a brick wall with lime plaster levelling. Outside is lime pointed with lowered hrpund levels. Building regs made me do it and there are no visible issues after only 10 years. East of England though and sheltered by eaves.

I've never been that happy with the idea of those NHL adhesives securing the wood fibre boards. I'm aiming to get my float coat perfectly flat, and the 40 - 60mm boards have a bit of 'give' in them anyway.

Good to hear your installation is holding up well. I'm not sure my BC would be too pleased if I decided to abandon any insulation at all.

 

[Lacan07]

Here are some recent papers evaluating the condensation risks associated with Wood fibre boards, in case anyone is coming to subject for the first time and interested.

https://historicengland.org.uk/cont...itoring-thermally-upgraded-victorian-terrace/

https://assets.publishing.service.g...082ac9c18f/6.03_DEEP_Moisture_Risk_Report.pdf

 

[Lacan07]

Thing about WUFI is that I would have absolutely no idea how to model the existing shell of this building so it would be impossible to know how much faith to put in the output.

Aren't exposure zones for guidance on new buildings with thin blockwork skins? I'm in the most exposed zone which I'm sure was recognised when this house was built and is reflected in the thickness of the stone walls. Putting external defects aside it would take some amount of weather to saturate my 2' walls to the point that water was running down the inside. Drying it out again would be no picnic either.

You may be right about the exposed WF collecting moisture from warm internal air to some extent. My money is on the adhesive used to attach it being wrong in some way creating a barrier. Given that we have one example to look at its all pretty much just speculation.

I'm also wondering from which side the moisture is penetrating - outer or inner?

 

[Loop_26]

This is a really interesting thread to read as someone at the planning stages of an internal insulation journey. Thanks for sharing!

I have just about talked myself back from wood fibre due to a couple of reasons and I am now considering just using 40mm of insulating plaster. If the calculations I see online as correct, this will already make a big difference to the amount of heat lost through my walls.

Thanks again for this thread. Very helpful!

 

[Lacan07]

And I forgot to say, Happy New Year to all the PP regulars!

 

[Brad Oleary LDPR]

Apologies just catching up with all this, I've been away over the Christmas period.

So would you say this is partly an issue with locality? The properties you work on would seem to be more exposed to wetter weathers than some of us located down South. If memory serves there seemed to be a suggestion in the comments that the interface between different materials - mineral brick to organic wood fibre - may have caused the issue. I've been chatting privately with Simon T on the FB group and he favours Multipor as an alternative solution. Its certainly worth looking at, although I'm kind of gearing up toward wood fibre in the Spring.

Mineral Insulation Board – Xella Multipor - Back to Earth

Multipor mineral insulation boards are:-

www.backtoearth.co.uk

With 200 wet days a year, it’s definitely a different climate to the south and one that needs careful consideration.

 

[Tuffa]

Hello @Brad Oleary LDPR

I think saw your post shared on a lime related FB group. From memory I believe it stated that the boards had been installed six months earlier. I noticed that the boards in the photo's appeared to not be plastered.
Can you confirm whether I've remembered that correctly? I ask because I suspect plastering reasonably quickly after installation is a required step in order to prevent warm moist air getting to the cold surface of the wall. This could be the cause, or have contributed to the problem.

I'm keen to know because like Lacan07, I am considering WF for IWI...

Regards,
Chris

 

[stuart45]

There's a big difference between a lot of rain and a lot of driving rain on a wall as well. As a lot of the moisture gets in through the mortar joints, the size of the joints also makes a difference. With a lot of random rubble walls the larger joints are more likely to have shrinkage cracks.
With solid brick walls, although in theory all the joints are full, many of them contain half filled joints which allow a passage through to the interior plaster.

 

[Kearn]

There's a big difference between a lot of rain and a lot of driving rain on a wall as well. As a lot of the moisture gets in through the mortar joints, the size of the joints also makes a difference. With a lot of random rubble walls the larger joints are more likely to have shrinkage cracks.
With solid brick walls, although in theory all the joints are full, many of them contain half filled joints which allow a passage through to the interior plaster.

Absolutely, and it’s not just oop north… the rear gables of our place get hit by all the rain and weather. While we were back to brick, with a decent amount of wind driven rain, the inside face of the 9” brick was wet in various places. This was likely down to the mismatch of poor pointing, which is on the list, but the patch locations didn't equate to obvious external weaknesses, to illustrate how far water can track inside the fabric of the building. These are also very very thirsty bricks…!