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Housing - New Build: Alternative to lime render (indoors) on strawbale

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      CommentAuthorjoe90
    • CommentTimeMay 16th 2009
     
    I am planning a new build, timber frame, with straw bale infill and I have been quoted £50 per square metre for lime rendering (3 coat). With regard the inside of the bale walls I am looking at reducing costs if possible as long as it does not compromise the building as a whole. I am thinking of inserting the face of the bales 20mm back from the timber frame,coating the bales with 20mm of clay (to fireproof etc) level with the timber frame then plasterboarding to frame and plaster coat. Also possible would be thin coat of plasterboard adhesive to glue boards to (dry) clay.

    I could save myself about £25 per square metre because more of this work could be done myself (will be retired with nothing better to do than build my own house) as this saving is in the region of £2000 it has got to be worth thinking about.

    My questions regarding this kind of construction would be will it interfere with the vapour permiability of the bale walls (they will be lime rendered outside or clay sealed and timber clad) and how will it affect the thermal mass of the walls.

    all comments greatfully recieved!
    • CommentAuthorbiffvernon
    • CommentTimeMay 16th 2009
     
    I'm doing a timber and straw bale build at the moment. We are plastering with earth. Will finish with limewash. Total cost for the 50 square metres = one bag of lime (+ labour).

    I suppose it depends on whether you want the boringly flat surface that a sheet of plasterboard delivers, or not.
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      CommentAuthorjoe90
    • CommentTimeMay 16th 2009
     
    I do like a flat finish but perhaps that is because that is what I have been programmed to accept???. My worry is DIY earth/clay/lime as I have not done this before and cant afford to get it wrong, Its the "mix" and "materials" that I have not worked with whereas I can fix plasterboard and my mate is a plasterer.

    Anymore comments please
    • CommentAuthorbiffvernon
    • CommentTimeMay 16th 2009
     
    You can afford to get it wrong because it doesn't cost anything. In fact it save you money because the work involved in mixing means you can cancel the gym subscription. If it goes wrong then you can scrape it off and start again. Start with a wheelbarrow full of subsoil taken from about 6 inches below the top of your garden. Add a bucketful of straw (I suppose you may have to pay your nearest farmer/horse owner a quid for a bale). Mix well, add water and mix much more till it's all a sticky gloopy mess. Then enjoy.
    • CommentAuthorCWatters
    • CommentTimeMay 16th 2009
     
    Joe90 - I'm no expert but do you need the 20mm of clay to fire proof it? Would say two layers of 15mm pink fire resistant plasterboard be sufficient?
    • CommentAuthorbiffvernon
    • CommentTimeMay 16th 2009
     
    Much better to have a layer of clay actually embedded in the straw rather than plasterboard next (ish) to the straw leaving an air gap.
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      CommentAuthorjoe90
    • CommentTimeMay 17th 2009
     
    Like biffvernon I think the clay embedded in the straw would be better (for fire resistance and thermal mass) and my mention of the plasterboard adhesive was also to link the plasterboard to the clay and straw so that there mass was linked. What I dont want to do is have a lightweight structure (plasterboard) not linked thermally to the rest of the wall. Also what is the permiability of plasterboard compared to lime?
    • CommentAuthorCWatters
    • CommentTimeMay 17th 2009 edited
     
    Posted By: joe90 What I dont want to do is have a lightweight structure (plasterboard) not linked thermally to the rest of the wall.


    Playing the devil for the moment..

    Why would you want it linked thermally? Insulation stops two objects being linked thermally. Why would you want the insulation reduced?
    • CommentAuthorCWatters
    • CommentTimeMay 17th 2009 edited
     
    Posted By: joe90Also what is the permiability of plasterboard compared to lime?


    Devils hat still on...

    I'd say foil backed plasterboard is likley to be a better vapour barrier and so more likely to stop moisture penetrating and condensing in the structure.

    Devils hat off...read this..

    http://www.cc-w.co.uk/Documents/Swearingham-moisture1.pdf
    • CommentAuthorcontadino
    • CommentTimeMay 17th 2009
     
    Lime rendering's not that difficult with a bit of practice and some advice from your plasterer mate, I'm sure you'd be able to DIY it. The cost of the materials doesn't have to be very expensive either, especially if you slake it yourself. I don't know what the costs are in the UK, but if you practiced on an unobtrusive bit of wall and it all had to come off for some reason, I'm guessing it would only be a couple of quid.
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      CommentAuthorjoe90
    • CommentTimeMay 17th 2009
     
    CWatters, re your comments above, during my reading on straw bale building it is generally accepted that fairly high vapour permiability of straw with lime rendering both sides is a good thing but it is encouraged that the permiability of the inside skin is slightly lower than that of the outside (this is so that any moisture/vapour within the bale is driven outward) and that the lime rendering on the inside adds to the mass. What I did not want to do by using plasterboard was detatch the inside skin from the bales to interfere with the wicking effect of the wall structure. Also during my reading any form of vapour barrier is frowned on. Thanks for the link above, really good comments on bale walls and their properties. I think I will contact amazon nails to see if I can book a lime plastering course for myself!!!

    biffvernon:- I have never been to a gym in my life, never had the time, always busy (like you no doubt???)

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