Gutex Thermoroom v Steico Internal Woodfibre Insulation Board

[RobertG]

Hi,

 

I was wondering if anyone could throw some light on the comparison between these products. I've had the Gutex specified for my job but the Steico seems to be considerably cheaper. I'm assuming there's a good reason for this but I just don't really know the products. 

 

It's for internal insulation on a solid stone and rubble wall dubbed out with lime mortar and then a Diathonite insulating plaster. 

 

Thanks 

 

Robert

[RobertG]

Bumping this up👊

 

[torre]

We used either Steico or Schneider internally, not heard of Gutex but they look interchangeable to me.

[jfb]

I went with the basic Steico and it has worked well.

non tongue and groove but foam filled any gaps

 

why diathonite plaster? Can’t you just use slightly thicker wood fibre? Cheaper for same result.

i just used nhl lime and sand for the internal render.

Edited November 17 by jfb

[RobertG]

8 hours ago, jfb said:

I went with the basic Steico and it has worked well.

non tongue and groove but foam filled any gaps

 

why diathonite plaster? Can’t you just use slightly thicker wood fibre? Cheaper for same result.

i just used nhl lime and sand for the internal render.

Hi JFB, 

 

Thanks for the reply. I get your point re the diathonite - I must look into this and see if it's an option. The architect has spec'd this for the the external walls: Listed from the final coat to the outside of the wall. 

 

1. 25mm Diathonite Insulating Plaster 2. 80mm Gutex Thermoroom Wood Fibre 3. 15mm Diathonite Insulating Plaster 4. 500mm Granite 5. 19mm Lime Plaster (SPAB value).

 

There's a lot of insulating plaster which will be very expensive but these products have been approved by Building Control so there'll have to be an alternative that meets these u values. I'll have to investigate further. 

[Lears]

I’m looking at the same thing right now. Wood fibre IWI and after looking around, Mike Wye and Steico seem the best bang for buck. I can’t see any difference in performance of wood fibre in all honesty once you confirm it’s the same dimensions and thermal properties…

 

Similarly, eco building’s eco wall suggest 30cm diathonite but it really does bump the cost up per sqm. I’m leaning towards just using a stickier lime mix with some additives to increase thermals a bit as the adhesive layer and leveller in one but still researching - there might be a good reason that’s not recommended…

[jfb]

19 hours ago, RobertG said:

There's a lot of insulating plaster which will be very expensive but these products have been approved by Building Control so there'll have to be an alternative that meets these u values. I'll have to investigate further. 

I think you have to be careful with old solid walls that you don’t risk interstitial condensation if you use too much insulation. I generally just used 80mm boards with normal lime render for the finish and levelling coats. Didn’t have any problems with building control but then I was going over building control specs for roof and under floor insulation as well.

 

[RobertG]

On 17/11/2025 at 21:56, Lears said:

I’m looking at the same thing right now. Wood fibre IWI and after looking around, Mike Wye and Steico seem the best bang for buck. I can’t see any difference in performance of wood fibre in all honesty once you confirm it’s the same dimensions and thermal properties…

 

Similarly, eco building’s eco wall suggest 30cm diathonite but it really does bump the cost up per sqm. I’m leaning towards just using a stickier lime mix with some additives to increase thermals a bit as the adhesive layer and leveller in one but still researching - there might be a good reason that’s not recommended…

I've seen mixes of quicklime, hemp and vermiculite used as a good alternative to Diathonite and can offer a substantial saving but whether BC would accept this is unknown to me. I'll keep looking.