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    • CommentAuthorgoodevans
    • CommentTimeMar 6th 2017 edited
    Decisions start off sounding easy but then when you look into the details...

    So single skin blockwork wall + EWI has been decided. - easy.

    I understand 190mm thick external blockwork is required as a minimum. - regs - easy

    To avoid unnecessary delays/costs the following choices present themselves:

    go for a 390x190x190 block - if they can be found
    go for a 440 x 215 x 190 block
    go for 440 x 215 x 215 block which appears to be more common and easier to purchase (as are lintels for this thickness).

    Is it better to go for Dense Concrete, light aggrgate or aircrete - dense gives me thermal mass, aircrete gives insulation value. I also understand that a wet plaster on aircrete is not the preferred combination for plasterers.

    A full size dense block is 35+ Kg - is this an efficient block to lay in terms of manpower? If not - is it any better to lay blocks on their side?

    Should I consider thin joint - it's a relatively small project - there may be no pre-existing experience available to me here - at present I suspect the benefits of thin joint would not overcome the dis-benefits.

    If I know the block system I can set the openings to coordinate and save on block cutting and general faffing about. I want to make the building fit the materials - it seems sensible to do this but only if the materials I will need when the time comes will be readily available at a sensible price.

    Words of wisdom/experience would be appreciated.
    • CommentAuthorbarney
    • CommentTimeMar 6th 2017
    Well, your structural engineer will have determined the wall thickness etc , however

    You can buy 7kn blocks at 440 x 190 x 215 but they are bloody heavy - 35kg plus (when dry)

    At risk of loosing a bit of space, I'd use 440 x 100 x 215 which gives you a bit of flexibility in terms of "block on flat" or 2 on edge (probably with full bed reinforcement every few rows)

    Cutting 100mm blocks is easy with a sharp bolster and a good lump hammer - matter of a few seconds

    You need to be more sensitive to dims when using facing bricks (many buildings would be set out for "brick dims" including the window and door openings

    For EWI, I wouldn't worry about thin or thick joint

    Plasterers hate rendering on Celcon or similar - and it will always crack


    look at fibolite 190mm or 140mm ( ive done single storey work with 140mm)
    good key, not to heavy
    some where between a medium dense and an aerated.
    also these in order of preference are worth a look ,
    Fenlite (some recycled aggregates)
    • CommentAuthortony
    • CommentTimeMar 6th 2017
    Aircrete blocks tend to crack too easily in my book, avoid them at all costs.
    • CommentAuthorMarkyP
    • CommentTimeMar 7th 2017
    aerated are to be avoided, as others say. plastering them is hard work, they need a really good sealing primer which adds time, and then 6 months later the blocks will crack along with your plaster. This is why the volume house builders always dot and dab - it's cheap, fast and hides all the cracks in the blockwork.

    I've used medium density aggregate blocks on my extension. There are loads of choices, from memory I think the medium density stuff is typically in the range of 1350 - 1550 kg/m3. Consider also the additional thermal mass of medium density blocks, in most cases I think this would be desirable, especially with EWI. Your brickies will thank you for going with a standard format block 440 x 215 x 100, these are on the heavy side but perfectly manageable. Also your local builder's merchant will likely hold stock which can be a factor on a big job as you can get deliveries quickly, you dont want to get held up waiting for a follow on delivery of exotic sized blocks.

    lastly, have a chat with your brickie and ask what he would use. My brickie was much happier when I told him it was medium density and not the aerated on the architect's drawings. I think aerated are a pest to lay in warm weather as they suck all the moisture out of the mortar.
    • CommentAuthorgoodevans
    • CommentTimeMar 7th 2017
    Would you really make up a 225 thick wall with 100mm blocks MarkyP - if so how often would you lay a block on it's side for bond?
    • CommentAuthortony
    • CommentTimeMar 8th 2017
    If I did it like that it would be four courses normal, wall ties on the second course, then two blocks laid flat, four more and then one laid flat under joists
    • CommentAuthorMarkyP
    • CommentTimeMar 8th 2017
    must be all sorts of combinations, like Tony says. Your brickie will likely do it in a combination that suits other details like lintels, joists, openings and so on.

    We have an internal structural wall which is three blocks wide (mediume density aggregate) - made up of a course of 440 x 215 x 100 on side, then a course on edge, tied into the course on side. It's a monster of a wall and should provide some very useful buffering thermal mass as the it seperates a kitchen and sitting room with a good deal of south facing glass.
    • CommentAuthorgoodevans
    • CommentTimeApr 17th 2017
    Sorry to resurrect this thread during the Easter break - but what disadvantage would a 215mm wall built entirely with blocks on their side with a stretcher bond have over Tony's method above. My thinking is that a simple stretcher bond wall would be easy to inspect and difficult to get wrong.

    Would you have the mortar pointed flush on the eps/ewi side and on the wet plaster side? presumably flush pointing would remove some of the convection paths behind the eps.

    I have walls that are 11.5m long and 15m long - I believe these will need expansion joints. My architect has suggested placing these up one side of the doors on each of the walls. Although they would be less obvious here is there any advantage in placing the expansion joint mid panel - perhaps where an internal wall is located. Is it rare to have some sort of expansion beading in the wet plaster on the inside of the building - I don't recall ever having seen one?
    • CommentAuthortony
    • CommentTimeApr 17th 2017
    Above one side of the door for me with a slip lintel and slip ties up the join.

    I hate blocks laid flat, my engineer would not allow them. It is not at all easy to get full proper mortar bed joints with laid flat blocks.
    • CommentAuthorgoodevans
    • CommentTimeApr 17th 2017
    Thanks Tony I see - more important to get the bed joints correct than the vertical joint between the two 'skins' - In fact should I be concerned if the brickies left mini cavity's, 4 blocks high, 10mm thick with your scheme (provided they used ties).
    • CommentAuthortony
    • CommentTimeApr 17th 2017
    I see no problem with that.
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