Home  5  Books  5  GBEzine  5  News  5  HelpDesk  5  Register  5  GreenBuilding.co.uk
Not signed in (Sign In)

Categories



Green Building
"The most popular book on green building in the UK today."
New fourth edition in two volumes!

Order both books now for the combined price of just £9.95
and free delivery!

(free delivery applies to UK addresses only).

Or get both books for just £7.90 if purchased at the same time as a subscription to Green Building magazine





Vanilla 1.0.3 is a product of Lussumo. More Information: Documentation, Community Support.

Welcome to new Forum Visitors
Join the forum now and benefit from discussions with thousands of other green building fans and discounts on Green Building Press publications: Apply now.




  1.  
    I was planning on using a wood wool carrier board for lime plaster on my internal walls. However, it's quite expensive. Also, I've just spoken to a supplier who says that they had problems with cracking with lime plaster and suggested that we use wood fibre instead. This needs to be thicker, or used in conjunction with a backing board. It is all getting quite complicated. Had anybody used any of these systems, and do they have any advice please?
    •  
      CommentAuthordjh
    • CommentTimeJul 14th 2017
     
    Posted By: ComeOnPilgrimI was planning on using a wood wool carrier board four lime plaster on my internal walls. However, it's quite expensive. Also, I've just spoken to a supplier who says that they had problems with cracking with lime plaster and suggested that we use wood fibre instead. This needs to be thicker, or used in conjunction with a backing board. It is all getting quite complicated. Had anybody used any of these systems, and do they have any advice please?

    We used woodwool boards everwhere we needed to render that wasn't directly over straw bales. That includes using woodwool boards over woodfibre, to get a better key surface for the lime.

    We haven't seen much cracking, just a few bits from the corners of windows and in the corners of the building.

    Cracking in lime is all to do with the exact mix, application and drying, IMHO. In other words all to do with the skill of the plasterer. Which supplier advised you? (whisper if you wish)
    • CommentAuthorjfb
    • CommentTimeJul 14th 2017
     
    I've used wood fibre boards on a farmhouse renovation. I will be using them again on other buildings. There is quite a difference in price between different boards. Do you have stone walls? Are they back to stone/brick or is there any render/plaster on walls?
  2.  
    Posted By: djh
    Cracking in lime is all to do with the exact mix, application and drying, IMHO. In other words all to do with the skill of the plasterer. Which supplier advised you? (whisper if you wish)

    The supplier was one based here in Oxfordshire. It may be no coincidence that they are owned by one of the main suppliers of wood fibre boards!

    However, I can see how a board that is mainly made of cement is going to be more rigid than a wood fibre board, and hence more prone to cracking. As a wood fibre board is quite flexible, it could move with the lime plaster.
  3.  
    Posted By: jfbI've used wood fibre boards on a farmhouse renovation. I will be using them again on other buildings. There is quite a difference in price between different boards. Do you have stone walls? Are they back to stone/brick or is there any render/plaster on walls?

    We have hempcrete external walls which are fine to lime plaster straight onto. The issue that has been bugging me is what we do with the internal walls (it's a new build). We haven't built them yet, but we will do imminently, so I'm casting round for some ideas.
    •  
      CommentAuthordjh
    • CommentTimeJul 14th 2017
     
    Hmm, woodwool boards are £6.80/m² whilst UdiSPEED are £16.49/m² and you think woodwool boards are expensive?
  4.  
    I think it's possible to get wood fibre boards more cheaply than that, but even so, that does not make the woodwool boards cheaper. I'm sure there's a better solution!
  5.  
    600 x 1350 x 40mm thick wood-fibre board £5.98 + carr + VAT from a purveyor of natural insulations. Whisper me if you want exact details.
  6.  
    Price wise, I can get a 2400 x 600 x 15 mm wood wool for £7 a board, 25 mm for £9 a board.

    I'm still not sure which is best though. Wood fibre at 40 mm adds quite a lot of depth to the walls and ceiling.
    •  
      CommentAuthordjh
    • CommentTime7 days ago
     
    That's a good price. 15 mm is fine for internal use and the lighter weight makes it easier to handle; 25 mm is for external use.
  7.  
    You could probably use 20mm WF, at £3/bd (+ carr and VAT) if the stud spacings are OK. I sugg'd 40 as you had expressed concern about needing a backing board.
  8.  
    Thanks @Nick. What spacings would you suggest to be suitable for a thinner wood fibre board? Also, I have some rigid insulation in the roof that I was planning on putting a carrier board over to plaster. Here space is at a real premium, so the thinner carrier the better. It is supported, but the board will be hanging vertically, so perhaps there will be some bowing if I used a thin board?
  9.  
    We've used 15mm wood wool boards for the internal stud walls and 25mm boards for ceilings (as advised by manufacturer). We've seen no cracking in the lime plaster and it's been up for a number of years.
  10.  
    Here is the response from a manufacturer of wool boards:
    'I’m really surprised at that statement since that is the main use of these boards in the UK. It’s also not a sensible reason as I’ll explain below.



    Whether cracking between render boards happens or not is determined by the sub-structure not the boards. If the timber frame is expanding and contracting significantly, whatever boards you have on the structure are going to be pulled and moved so the board type is totally irrelevant to that issue. Cracking happens because of movement in the frame pulling the boards apart and is usually the frame which causes this to happen – factors such as whether the timber is cut parallel or perpendicular to the grain of the wood even have an influence.



    X basic boards are 600 x 2000mm which is half the size of the traditional render boards which are 1200 x 2400mm so if there is excessive movement in the sub-structure and the boards to get pulled apart, smaller boards have twice as many joints so that could be what this person is getting at. Poor installation highlighted by having twice as many joints? Nevertheless, if the structure is well made, the rendering is done properly with a layer of mesh and the timber used to make the frame has a low coefficient of linear expansion, the board type has absolutely no bearing on this problem whatsoever.

    ……..actually, that’s not entirely true….. if you were to use a board susceptible to significant expansion/contraction (or to be more precise, with a linear thermal expansion coefficient greater than that of the timber frame) the board could have quite a negative effect. Such materials however are not suitable for external use such as wood fibre board or even woodwool board bonded with magnesite rather than cement swell when they absorb water. An X cement-bound woodwool board will not swell due to water absorption. An X cement-bound woodwool board will exhibit some thermal expansion and contraction but less than you would find in hardwood timber. Remember, unlike say wood fibre boards, although they are still wood based, X boards are cement-bound boards and therefore not subject to the same problems you would get with pure wooden boards.



    Nevertheless although this is a tried and trusted construction method neither us (or I suspect, our successor) , nor the render company nor the supplier of the mesh or the timber are likely to give you any guarantees that there will be no cracking – there are just too many factors – mainly installation to consider. But as I say, this problem has nothing to do with the boards so you could get this with any board you could think of. In the last five years of being X's agent in the UK I can honestly say that we have never once had a single phone call from any customers saying that they experienced cracking on X boards with lime render.
  11.  
    Another option we have is to use clay plaster on the walls. Presumably this is slightly easier to fix than lime plaster if there are any cracks?
    •  
      CommentAuthordjh
    • CommentTime4 days ago
     
    Posted By: ComeOnPilgrimAnother option we have is to use clay plaster on the walls. Presumably this is slightly easier to fix than lime plaster if there are any cracks?

    You seem to be looking for any possible way to avoid using a tried and tested solution!

    Clay plaster has the advantage (or is it a disadvantage?) that it doesn't cure but just dries, so you can add water and turn it back to mud. But the techniques for patching lime plaster have been improving for thousands of years, so they're well established and work well. Certainly around here it's a lot easier to find a skilled lime plasterer than a skilled clay plasterer.
  12.  
    @djh, fair enough! I just wanted to investigate all options as a board that is relatively expensive and might be prone to cracking is worrying me somewhat.
    •  
      CommentAuthordjh
    • CommentTime4 days ago
     
    To be fair I just watched our local news programme, which had an article about a lady that has restored her old cottage by learning wattle and daub techniques. So apparently clay plaster is 6000 years old! A bit older than lime, which I suppose isn't too much of a surprise.

    I'm still not clear why you want lime and/or clay on your internal walls rather than gypsum? I've been assuming that the internal walls are those that aren't the inside of external walls. For the inside of external walls, I do understand the need for lime or clay with certain wall constructions. But for walls that are truly internal, I'm not sure what the concern is?
  13.  
    I was thinking that we'd need consistency between the internal and external walls, so whatever was used on the external hempcrete walls, we'd use on the internal walls. I was thinking it might look a bit odd to have lime / clay on some walls, and then gypsum on others in the same room.
    • CommentAuthorjfb
    • CommentTime3 days ago
     
    i would second the relevance of the difference in appearance of lime render to gypsum finish - they can look very different.
    •  
      CommentAuthordjh
    • CommentTime3 days ago
     
    The internal side of my external walls is covered in lime plaster (my airtighness barrier). My truly internal walls and ceilings are conventional studwork, plasterboard and gypsum skim. They are all painted with the same clay paint, which is what you see. I haven't had any visitor that has even noticed the difference, let alone make any comment.

    Now the internal lime plaster does look considerably different to the external lime render, because internally it's been smoothed pretty flat whilst externally there's some grit visible on the surface, and the lumps and bumps are also somewhat more obvious. But how lime looks depends on what product/mixture is used and how it is applied.
  14.  
    edit quote
    I had another conversation with the technical person from a wood wool manufacturer. He said that the company that sells wood fibre board have never sold wood wool board. It may well have been a bit of marketing patter (to put it politely!) that I fell for.
Add your comments

    Username Password
  • Format comments as
 
   
The Ecobuilding Buzz
Site Map    |   Home    |   View Cart    |   Pressroom   |   Business   |   Links   
Logout    

© Green Building Press