NHL v Air lime

[RenoAl]

Morning all. We were planning on doing a woodfibre retrofit to our solid wall church conversion. We had a package set up with Mike Wye to provide all the materials for this following their IWI system as follows:

1. SecilTek Reabilita Cal RB
2. SecilTek Isovit Lime
3. STEICO Internal / Therm Wet
4. H3 Insulated Masonry Fixings
5. STEICO Therm Wet Reveal Boards
6. PVC Corner Bead (mesh wing)
7. PVC Window Frameseal Beads
8. Fibre Glass Render Mesh
9. SecilTek Reabilita Cal AC Fino

We recently had a historic building consultant come to look at the property and he vehemently told us to stay away from woodfibre as it's not working long term and falling apart inside walls/turning to mush and he is seeing this constantly so we should stick to a natural method such as insulated plaster. Apparently historic England is aware of the wood fibre failings and is now changing its recommendations for good practice however I can not see evidence of this. Further to this use of NHL based materials for this is incorrect and we should be using hot lime mixes/air lime mixes only to ensure breathability and ensure the strength of the limes aren't going to keep on increasing. This chap was SPAB affiliated so I assume he knows what he is talking about, however this seems contrary to what everyone else is saying and that the system above is workable.

Thoughts?

 

[fernicarry]

Insulating plaster is less effective than wood fibre, roughly half, so your build up will be twice as thick for the same performance. Potentially a lot more labour required to get it up there.

I wonder if as a consultant he looks at more cases of failure than success and is suffering from "survivor bias"? Does he say what's causing the failures?

Not gonna' touch the NHL question...

 

[RenoAl]

Does he say what's causing the failures?

NHL mixes curing with increasing strength over time which has reduced the permeability, as such moisture increases in the WF and between layers of the IWI causing it to disintegrate essentially. I spoke to Mike Wye and they have never come across this and have instead said it is commonly install error when they have people come back to them and have never come across this reasoning before. So I understand your survivor bias take!

Not gonna' touch the NHL question...

Too controversial, or am I just barking up the wrong tree...

 

[fernicarry]

Too controversial, or am I just barking up the wrong tree

You'll get strong opinions both ways on here...

For my building I don't think NHL is inappropriate. Very hard stone, heavy weather load and not really suffering from any damp problems. For other situations it may not be so suitable. Ask me in 30 years if I regret it...

 

[RenoAl]

You'll get strong opinions both ways on here...

For my building I don't think NHL is inappropriate. Very hard stone, heavy weather load and not really suffering from any damp problems. For other situations it may not be so suitable. Ask me in 30 years if I regret it...

Thanks for the response. It seems it is opinion everywhere and a lack of consensus. Albeit I am happy with lots of opinions to make an informed decision of at the least!

 

[a twig]

Same camp as @fernicarry - previous house built of white lias with a high iron ore content so hard as anything - needed an SDS just put a shelf up. Used NHL2 or NHL3.5 for everything.

Here where we have soft reds I use NHL2 or lime putty based mortars depending on application

 

[Kearn]

There are a few plasterers who have lately been posting the results of fairly recent (less than a year or so) failures of woodfibre boards, on the inside of stone/brick walls. The challenge being, the change in material, density and ability to move wet moisture. This would be in the case of wet areas, high capillary original structure that gets wet and needs to dry inside and out, and this moisture gets to the interface with the woodfibre and cannot go anywhere quickly enough and sits within the middle of the new wall thickness, whereas previously would have evaporated from the inner surface. The boards disintegrate.

It has its place, I don’t believe sticking it to the inner face of a solid wall is it.
I’ve used it as the outer plaster surface for timber infill panels. That said, it has alleged rain resistance which is an immediate red flag (not all variants do). Caveat - I maybe regret this…

It’s key to note, the difference in wood fibre boards and batts. The boards are bonded differently and should be used with caution. The batts I’ve used in place of proper sheepswool for insulation fill in some of my infill sandwiches, and I’ve had first hand experience of it getting soaked and then drying out very quickly and completely. The boards, not so much.

I’ll be honest, the list of products in your post would make me run a mile. Too many unknowns and experiments that just haven’t been proven, but are starting to show issues. Also all very costly.

I’d listen to the person who is giving experienced advice, not selling product.

A solid wall needs to be dry first and foremost, then it insulates. Make it wet, it conducts.

If you want to use Mike, ask about their thoughts on other internal insulating approaches, perlite mixes etc

I would get something non nhl plus chemicals in a bag, and build a nice thick layer up with some insulative inclusions.

If you want an alternative conversation and viewpoint, speak with Tim or Karl at Eden HotLime.

 

[RenoAl]

There are a few plasterers who have lately been posting the results of fairly recent (less than a year or so) failures of woodfibre boards, on the inside of stone/brick walls. The challenge being, the change in material, density and ability to move wet moisture. This would be in the case of wet areas, high capillary original structure that gets wet and needs to dry inside and out, and this moisture gets to the interface with the woodfibre and cannot go anywhere quickly enough and sits within the middle of the new wall thickness, whereas previously would have evaporated from the inner surface. The boards disintegrate.

It has its place, I don’t believe sticking it to the inner face of a solid wall is it.
I’ve used it as the outer plaster surface for timber infill panels. That said, it has alleged rain resistance which is an immediate red flag (not all variants do). Caveat - I maybe regret this…

It’s key to note, the difference in wood fibre boards and batts. The boards are bonded differently and should be used with caution. The batts I’ve used in place of proper sheepswool for insulation fill in some of my infill sandwiches, and I’ve had first hand experience of it getting soaked and then drying out very quickly and completely. The boards, not so much.

I’ll be honest, the list of products in your post would make me run a mile. Too many unknowns and experiments that just haven’t been proven, but are starting to show issues. Also all very costly.

I’d listen to the person who is giving experienced advice, not selling product.

A solid wall needs to be dry first and foremost, then it insulates. Make it wet, it conducts.

If you want to use Mike, ask about their thoughts on other internal insulating approaches, perlite mixes etc

I would get something non nhl plus chemicals in a bag, and build a nice thick layer up with some insulative inclusions.

If you want an alternative conversation and viewpoint, speak with Tim or Karl at Eden HotLime.

@Kearn thank you very much for your input. That marries up nicely with what the chap said but it's the first I have seen written on here of such failings.

Agree it is very very costly and given the lack of long term appraisals I am reticent to go for it having heard the consultants experience and a few others now. My only concern with insulated plasters are you do struggle to reduce the U-Value as significantly; that being said, I have lived in old houses my entire life and not one has had wall insulation so I do not know why I am getting wrapped around the axel on that!

I have seen Eden HotLime as they are fairly local to me in North Yorks. Will definitely have to get in comms with them.

 

[Kearn]

Too many people getting hung up on theoretical U values, and then looking at them in isolation from the rest of the building… a dry wall is the baseline target.
Adding insulation which may actually make it damp, completely negates the theoretical u value attainable, possibly making it worse than just the previously dry solid wall alone. With solid walls, you want to try to maintain the similar thermal properties of the existing material with any additions, having big step changes isn’t ideal.

Some of this is the emperors new clothes I fear, and a costly exercise upfront and then potentially again further down the line.

There just isn’t the data yet or longevity to say either way.

But issues do seem to be showing up.

Not having issues doesn’t make it right, I’ve had gypsum plastered walls and concrete floors that haven’t caused issues in their situations, doesn’t mean I would choose to do that.

Certainly do some ringing around and talking through, both with suppliers and plasterers. It’s a big effort, big cost and massively important bit of the work to get right.

 

[Lacan07]

@Kearn @RenoAl





Its rather a coincidence that this post has come up as I stumbled upon the same topic on a Facebook group the other day and intend to open a new thread here on PP to discuss further. Its a bit of drag that these grumblings about wood fibre have started to surface now as ever since I purchased my property I had intended to utilise the boards for my IWI, and having started work downstairs I'm now prepping the walls to mount the boards in the Spring.

I thinks its time to have a serious discussion about Wood fibre board and its alternatives and I intend to do some serious digging.

 

[Itchinfilth]

For those on Instagram an account called 'Lake district property renovator & heritage builder' has done some recent videos with issues encountered on woodfibre boards for IWI on solid walls. Not a pretty picture.