Woodfibre insulation with an airgap

[stamas01]

Hi all,

I bought lots of wood fibre insulation to cover my walls from the inside. The initial plan was to straighten the walls using a send and lime putty mix. After finishing a single wall, I realized that the amount of lime putty required is insane, let alone the price. I now regret I did not go with an airgap and a pir insulation.

I put wooden battens to the wall and somehow put my existing wood-fibre insulation on it, maintaining the air gap. My initial idea is to fix OBS bords on the buttons and somehow glue the wood fibre on the OSB. If anyone has a better idea, please share it here cause I am struggling. Of course, I could just put a plasterboard over my wood fibre, but then it would not be breathable. Given that I am now maintaining an airgap, breathability is not essential, but at the end of the day, I purchased wood fibre, so I would like to have it breathable.

Any suggestion is welcome.

Thanks,

Tamas

 

[malcolm]

What kind of wall do you have? I guess rough stone inside. Lime and sand are fairly cheap and there is not normally a lot needed to get to a smooth surface. OSB is really expensive these days.

I can't think of any reason why woodfibre wouldn't work on batons with an air gap. Just screw it to the batons using the woodfibre washers. i don't like batons hidden inside walls unless I'm sure they won't get wet. Everywhere I've done that the void has been ventilated.

I think some on here have even screwed the woodfibre directly on an uneven wall and that might be easier even if you have to put a bit of plaster on in the mounting locations. Worth keeping it off the floor with a few bits of slate so it can't suck up any water from the ground.

 

[a twig]

Yep, just fix straight to the wall - as the fibreglass washers are so big you place the board, wang through both the board and into the wall with a masonry bit, then rawl plug in and then screw with washer.

No need to drill boards, offer up, mark, take done, drill holes, fit plugs and then offer up the board again and try and line it all up

 

[stamas01]

Yep, just fix straight to the wall - as the fibreglass washers are so big you place the board, wang through both the board and into the wall with a masonry bit, then rawl plug in and then screw with washer.

No need to drill boards, offer up, mark, take done, drill holes, fit plugs and then offer up the board again and try and line it all up

if I fix ot straight to the wall there will be air gaps between the wall and the insulation. I was told that ot can lead to problems. Is that not the case?

 

[stamas01]

What kind of wall do you have? I guess rough stone inside. Lime and sand are fairly cheap and there is not normally a lot needed to get to a smooth surface. OSB is really expensive these days.

I can't think of any reason why woodfibre wouldn't work on batons with an air gap. Just screw it to the batons using the woodfibre washers. i don't like batons hidden inside walls unless I'm sure they won't get wet. Everywhere I've done that the void has been ventilated.

I think some on here have even screwed the woodfibre directly on an uneven wall and that might be easier even if you have to put a bit of plaster on in the mounting locations. Worth keeping it off the floor with a few bits of slate so it can't suck up any water from the ground.

Hi, so you can buy hydraulic lime that is not or less breathable then lime putty. Sand is cheap but lime putty is not. 2 walls needed at least 600£ worth of lime putty.

 

[Lacan07]

if I fix ot straight to the wall there will be air gaps between the wall and the insulation. I was told that ot can lead to problems. Is that not the case?

Yeah, if its not ventilated there's a chance you'll start growing mushrooms behind your wood fibre wall.

Can you not 'dub out' the major hollows in the wall to create a more even surface? It doesn't have to be a completely plastered wall.

 

[Lacan07]

Hi, so you can buy hydraulic lime that is not or less breathable then lime putty. Sand is cheap but lime putty is not. 2 walls needed at least 600£ worth of lime putty.

You can by hydrated lime from builders merchants and add water to create lime putty.

NHL (non hydraulic lime) is considered inferior to lime putty but is often roughly the same cost

 

[stamas01]

You can by hydrated lime from builders merchants and add water to create lime putty.

NHL (non hydraulic lime) is considered inferior to lime putty but is often roughly the same cost

Can you help me out wit NHL? There is usually a number following it like NHL 3.5 or NHL 5. Will it still be breathable if I mix it with sand exclusively without adding portland cement? If so would you suggest me to go with the 3.5 or 5 or something else?

 

[malcolm]

The NHL lime is breathable enough for most purposes. You should never mix it with cement as that would ruin it's properties. The numbers increase with hardness and 5 is the hardest and tends to be for floors. Everyone uses 3.5 as that's all the builders merchants stock. That's what I use and I did have the opportunity to dig some out after a couple of years to fit electrics and it was still softer than the 100 year old lime plaster and still nice and dry. It takes time to carbonate but plaster doesn't need to be hard.

Hydrated lime is a whole lot cheaper than NHL and is also available at builders merchants. It's the same but without an initial chemical set. People mix it with water to make putty. I don't have a lot of plastering left to do but regret not testing using it straight out of the bag instead of NHL.

 

[Lacan07]

Can you help me out wit NHL? There is usually a number following it like NHL 3.5 or NHL 5. Will it still be breathable if I mix it with sand exclusively without adding portland cement? If so would you suggest me to go with the 3.5 or 5 or something else?

As Malcolm says above...

I'll just add the traditionalists don't like NHL for two reasons, they believe it not to be as breathable as putty and also some research suggests NHL gets stronger over time, so an NHL 3.5 may eventually become a 5. This probably has greater implications for lime mortar if you're repointing soft reds bricks, for example.

Its probably important to note that NHL lime is the most specified lime by architects, etc in the last 10 - 15 years during this 'renaissance' period of old buildings. I always thought the research into the effectiveness of NHL was still on going but a traditional lime putty plasterer will tell you its a done deal!

I wasn't aware you could readily find NHL lime at builders merchants (I'm probably wrong!). It usually comes in powdered form and you add water. The other reason traditionalists don't like it is the new manufacturers on the block like 'Lime Green' add cement (allegedly) to their NHL products. They may well also add accelerants which makes it trickier (for the amateur) to work with. Lime putty, however, certainly gives you a greater working time.

Again, traditionalists don't much like hydrated lime putty because of storage issues. It can easily go off. If you choose to create some putty with hydrated lime when you've mixed it up just form a little 'bricket' and put it to one side. If it dries and goes rock hard you know its good to go. Storage problems solved.