GBEzine

1. • 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
   or
   go for a 440 x 215 x 190 block
   or
   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.
2. • 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
   
   Regards
   
   Barney
3. • CommentAuthorjamesingram
   • CommentTimeMar 6th 2017

    
   look at fibolite 190mm or 140mm ( ive done single storey work with 140mm)
   https://www.plasmor.co.uk/products/fibolite-fl
   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)
   Hemelite
4. • CommentAuthortony
   • CommentTimeMar 6th 2017

    
   Aircrete blocks tend to crack too easily in my book, avoid them at all costs.
5. • 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.
6. • 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?
7. • 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
8. • 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.
9. • 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?
10. • 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.
11. • 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).
12. • CommentAuthortony
    • CommentTimeApr 17th 2017

     
    I see no problem with that.
13. • CommentAuthorgoodevans
    • CommentTime5 days ago

     
    I've Just had some good news - I've chatted with an structural engineer and he said he can design all my structural walls with a 140mm solid block-work wall with a standard stretcher bond (however one wall may need a wind post).
    
    Unfortunately he has confirmed piles, ring beam and beam and block floor as being the most cost effective solution for us.
    
    As we have a simple rectangular building he suggests supporting the b&b beams on a steel angle bolted to the inside of the walls to save on cutting blocks between the beams. It means the blocks can be laid to screed level in one lift, then the steel angles then B&B, polystyrene, dpc, uvf and screed.
    
    Instead of movement joints in the long walls he suggested bed joint reinforcement every two courses of block to control cracks for the plasterwork and the render.
    
    As I intend using medium density blocks for the internal partition walls - is there any problem building them on top of the screed (B&B design permitting) - or do they need to penetrate the floor insulation and be directly supported by the B&B?
    
    any other comments welcome.
14. • CommentAuthorbarney
    • CommentTime5 days ago

     
    Sounds a bit mad - I'd not be opting for shelf angles when you have a perfectly good 140mm bearing surface on which to bed the beams
    
    Have you not looked at closure blocks at the beam ends - or even a bit of shuttering and cast closures in situ
    
    Unless you've designed the screed for it, again, I'd not build off it - usually you double up the beams to carry any masonry internal walls
    
    Again, matter of taste, but I'd put the insulation under the beam and block (fill the void from the over-site right to the underside of the beam
    
    You've not really described what you are doing so the above comments might be nonsense, but I'd be going with "build in" not "bolt in"
    
    Regards
    
    Barney
15. •  
      CommentAuthordjh
    • CommentTime5 days ago edited

     

    Posted By: barneyAgain, matter of taste, but I'd put the insulation under the beam and block (fill the void from the over-site right to the underside of the beam

    
    I don't think it's really a matter of taste. The only way to seriously reduce the thermal bridge is insulation both under and above the floor as I understand it. It also depends on why a beam and block floor is specified, of course. If it's because of risk of heave then there's no way I know of to fill the void. If it's radon risk then you wouldn't want to fill it.
16. • CommentAuthortony
    • CommentTime5 days ago

     
    I hate it, a LOT of weight on the bolts, I wouldn't do it.
17. • CommentAuthorgoodevans
    • CommentTime4 days ago

     
    OK - I will look again at the steel angle support of the B&B floor.
    
    A suspended floor is required because of heave.
    
    I am assuming that insulation systems that sit below the B&B are expensive compared to above the B&B - in addition finding them with 200mm or more of platinum eps below is even more difficult.
    
    I presume that stud partitions usually sit on top of the insulation and screed and was hoping to do the same with my thermal mass blockwork - but if this is not the done thing I will have too look at using stud walls instead and forgo the thermal mass.
18. •  
      CommentAuthordjh
    • CommentTime4 days ago

     

    Posted By: goodevansI am assuming that insulation systems that sit below the B&B are expensive compared to above the B&B - in addition finding them with 200mm or more of platinum eps below is even more difficult.

    
    There are some insulated B&B systems that use preformed EPS blocks resulting in some insulation beneath the beams. e.g. Beamshield. And others that use insulated blocks above the beams. e.g Tetris. I don't know much about their relative merits because a passive slab seemed much simpler in my situation.
19. • CommentAuthorbarney
    • CommentTime4 days ago

     
    Isn't it an EWI system - so the whole lot inside FT's "tea cosy"
    
    The only cold bridge is the long path through the wall to the founds ? - which exists in any case
    
    If the B&B combats heave then loose fill the void with EPS beads and have the B&B mass inside the thermal envelope
    
    You can still have masonry internal walls - just design the B&B for it
    
    As I said, I'd not be hanging a B&B floor off bolted shelf angles
    
    Regards
    
    Barney
20. •  
      CommentAuthordjh
    • CommentTime4 days ago

     

    Posted By: barneyIf the B&B combats heave then loose fill the void with EPS beads and have the B&B mass inside the thermal envelope

    
    I'm not having a go, just trying to make sure we're all on the same page. You're sure that loose-fill EPS beads will work as a fill against heave? It won't transmit force up to the floor? So it behaves like Cellcore etc. You'll put your PI insurance on the line and sign off the structure? And guarantee it remains effective as insulation?
    
    The insulation location is to do with humidity and mould growth, I believe.
21. • CommentAuthorgoodevans
    • CommentTime4 days ago

     
    BCO will insist on no material in the void (other than air). In any case EPS beads would exert a significant up force on the slab if the clay heaves, and if the clay shrinks the beads will not be against the B&B and as ventilation will be required ...
    
    If I insulate below the B&B it would have to be something like beamshield - I'll give them a call tomorrow to get prices but I don't expect they will compete with EPS over B&B.
    
    Cellcore plus is also an option and I believe does not require ventilation. but again will be expensive.
    
    There will be compromise - all I can do is make the best of it.
22. • CommentAuthorbarney
    • CommentTime3 days ago

     
    I'm not signing anything - I'm not offering advice in any contractual capacity :-)
    
    I was simply suggesting that it's credible the unventilated void can be filled with loose insulation (to combat heave) and retain the B&B within the thermal envelope - acting , as you suggest like cellcore would in a "heave" situation
    
    The construction will be EWI outside single skin, so the beam ends rest on the structure and remain warm, rather than on a proposed shelf angle - again, strongly suggesting an unventilated void is not a problem - discuss with BC
    
    Personally, I'd have no issues with that approach as a workable concept - particularly as the OP is wishing a lot of thermal mass in walls - so why isolate the greater mass of the floor ?
    
    As an observation I would have thought the installed cost of shelf angles would outstrip moving from EPS to a verifiable Cordek product
    
    As we don't know the heave potential, I would still examine EPS beads in an unventilated void, personally
    
    Regards
    
    Barney
23. •  
      CommentAuthordjh
    • CommentTime3 days ago

     

    Posted By: barneyI was simply suggesting that it's credible the unventilated void can be filled with loose insulation (to combat heave) and retain the B&B within the thermal envelope - acting , as you suggest like cellcore would in a "heave" situation

    
    Loose is not the same as compressible. Cellcore is an air-filled honeycomb and permanently deforms when heave forces crush it. Thus leaving a permanent air space if the ground subsequently drops. (some seasonal rainfall or tree removal/regrowth scenarios can cause repeated heave movements). Unless you can suggest the name of an engineer who will sign it off, it's a non-starter, IMHO.
24. • CommentAuthorbarney
    • CommentTime3 days ago

     
    Yes, I know what cellcore is - curiously enough I'm working on a project at the moment where it's failed spectacularly under a ground floor slab onto beams and piles
    
    There is evidence that it's already collapsed whilst the floor slab was being poured (although the slab is about 750mm thick for various reasons so an awful lot of weight imposed on the cellcore)
    
    I agree that loose is not compressible but as the void former doesn't play any part in supporting the B&B, I was simply postulating that a fill of EPS would give you a lot of insulation under the B&B even if it's not exactly fully filled - provided there is no ventilation - and why would there be ventilation
    
    I've no idea what the expected heave is - it may well be marginal anyway
    
    Didn't someone on here recently fill the void with EPS using a jetfloor B&B system ?
    
    Regards
    
    Barney
25. • CommentAuthorgoodevans
    • CommentTime3 days ago edited

     

    Posted By: barneyI'm working on a project at the moment where it's failed spectacularly under a ground floor slab onto beams and piles
    
    There is evidence that it's already collapsed whilst the floor slab was being poured (although the slab is about 750mm thick for various reasons so an awful lot of weight imposed on the cellcore)

    
    Cellcore comes in several different grades - the grade should be chosen to fail at a load just above the dead weight of the slab - what grade of Cellcore was used under the 750mm slab? It should have been the blue colour coded Cellcore - safe to support 24KN/m2 will fail at 32KN/m2
26. • CommentAuthorgoodevans
    • CommentTime3 days ago

     
    At best my clay will be a minimum of medium shrinkage clay but probably High shrinkage clay - so an equivalent void of either 100mm or 150mm will be required. I shall probably just opt for a worst case with a few mm of extra excavation and a if Cellcore is used a fraction longer cellcore downstands.
27. •  
      CommentAuthorfostertom
    • CommentTime3 days ago edited

     
    Just reading this important thread properly, having prefered to minimise blockwork for many years, so not up to date.
    
    

    Posted By: jamesingramlook at fibolite 190mm or 140mm ( ive done single storey work with 140mm)
    https://www.plasmor.co.uk/products/fibolite-fl" rel="nofollow" >https://www.plasmor.co.uk/products/fibolite-fl
    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)
    Hemelite

    New to me - I thought Leca blockwork was extinct. Their page
    https://www.plasmor.co.uk/products-services/techniclay-aggregate/focus-on-expanded-clay
    also a revelation - after years of banging on about Leca, had no idea there's a UK producer. The page is a model of good information. Plus other interesting, aware-looking services on
    https://www.plasmor.co.uk/technical-services.
    
    However, no tech info on the site at all - "coming soon" - are they a new or recently re-booted co?
    
    Fenlite 'includes' blast furnace slag in 3.6N/mm2 but looks like much less of that, more of 'natural' aggregate, in 7.3N/mm2 'structural', such as goodevans will be using.
    Blast furnace slag must be in ever-shorter UK supply, just like the power station ash discussed by Plasmor.
    (The other hope, bottom ash from waste burning, has not taken off because toxic - has become a disposal problem rather than an asset).
    
    Not clear what Hemelite is made of these days.
28. • CommentAuthorgoodevans
    • CommentTime3 days ago

     
    Thanks tom (but your link faulty)
    
    yep - at the moment that's my preference (price and supplies being reasonable when its required). With a reasonable density for thermal mass. A good all rounder.
29. •  
      CommentAuthorfostertom
    • CommentTime3 days ago edited

     
    Funny - the link Quoted direct from James' post, where it does work.
    
    Note, I've edited in a bit more discussion into my post.
    
    Medium density for thermal mass - could just be that rare 'sweet spot' occupied by Hemcrete?
30. •  
      CommentAuthorfostertom
    • CommentTime3 days ago

     

    Posted By: goodevansmortar 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

    good point. Nothing wrong with air voids that don't extend far - but these could zigzag a v long way.