IWI wood-fibre onto solid brick masonry: application methods?

[ectoplasmosis]

I'm looking to apply 60mm internal wood-fibre insulation boards to two walls of a 10sqm bedroom in my Victorian semi. The walls are south-facing.

 

The walls are currently covered in plasterboard applied via dot & dab, so this will be coming off exposing the bare brick.

 

What would be the best method to apply the wood-fibre IWI, and which surface finish to use? As the bedroom is already small, I'd like to avoid building a timber cavity. Can I apply the boards directly to the exposed brick? I was thinking to then use Lime Green Solo One Coat lime plaster on top, no paint. Would I need to treat the boards with anything before applying the lime plaster finish?

 

I'm very new to all of this, so apologies in advance if I'm asking the obvious!

[Redbeard]

Do a 'parge-coat' (air-tightness layer) of lime plaster over the bricks first. Minimum 6mm thick, ideally. If you can, take up floorboards so that you can extend the parge coat down to the ceiling of the room below, for 'picking up' later when you do the rooms downstairs - however much later that may be. Leave to dry. 'Butter' the back of the boards with lime plaster as an 'adhesive' using a 6mm or 10mm toothed trowel (6mm if you vcan hold the trowel at 90 degrees to the wall - not the natural way - or 10mm if you tend to hold at a shallow angle, as you will be 'closing down' the furrows to 6mm or less anyway) and apply the boards, being careful to ensure that no plaster gets 'picked up' in the joints - plaster is not as good an insulator as WF!

 

Then apply lime plaster as recommended, with mesh reinforcement. I have never used Lime Green products, and certainly never plastered WF in 1 coat. Not to say it would not work, but the way I was taught, for the room-side, not for the adhesive layer (with Baumit products) was:

 

- Toothed trowel coat

- Glass-fibre mesh laid gently onto toothed coat. Allow to stiffen very slightly

- 'Wet-on-wet' coat of plaster to 'hide' the mesh as much as you can (IME you won't hide it completely)

- When 'dry' (1 day minimum) a further coat to hide any residual 'ghosting' of the mesh.

- Allow 4 days to dry (you may get away with 2 in really warm weather before coating with (in my case) Kalkin Glatt, a very thin finish plaster, which neither 'builds' much, nor hides much, so get the previous coat of base-coat nice and smooth.

 

This is not an advert for a particular product! I just find this brand easy to use and have seen no reason to chance in 9 years.

 

Would some pictures help?

 

Edited December 5, 2023 by Redbeard
typo

[ectoplasmosis]

That's a fantastic reply, thank you!

 

Some pictures would be great if you have any.

 

We are committed to the Solo One Coat lime plaster product for the final surface finish, as we're using it in many other areas of the house, so would be great to have a uniform appearance. More than up for using Baumit as the underlying adhesive etc.

Edited December 5, 2023 by ectoplasmosis

[Redbeard]

OK, pictures follow later, if only to prove that I am one of the world's worst photographers!!

 

I checked the data sheets for 'Solo one coat' and see that, as I was sure must be the case, they do require mesh:

Common Uses

• Woodfibre Insulation Boards: simply skim on Solo in 2 passes with mesh in between, around 10 mm thick.

So effectively they are suggesting the same as I do, which is that you 'split' the base-coat with mesh. As I described it layers 1 and 2 of plaster are in effect 2 halves of the same coat. The difference is that (a) they don't suggest another coat of base-coat (arguably not necessary unless you get mesh 'ghosting' through) and therefore (b) that you have to trowel up this 'split coat' as your top-coat.

 

 

[ProDave]

1 hour ago, ectoplasmosis said:

More than up for using Baumit as the underlying adhesive etc.

Search the site for my threads on external Baumit render problems and you might change your mind.  They were totally disinterested in helping to find out what the problem was.  I could not recommend a company that won't help at all when their product fails.

[Redbeard]

18 minutes ago, ProDave said:

Search the site for my threads on external Baumit render problems and you might change your mind.  They were totally disinterested in helping to find out what the problem was.  I could not recommend a company that won't help at all when their product fails.

 

In any case, @ectoplasmosis, if your are comfortable with using the Lime Green I see no reason in principle (I have not read their blurb) why you should not use the LG product for the parge coat.