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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorShevek
    • CommentTimeMar 9th 2013
     
    Generally EWI systems utilise a bead at corners, giving a nice straight 90ΒΊ corner (at building corners and around window openings).

    Is it possible to round these edges in some way instead? Not necessarily big round organic curves, rather just taking the sharpness out of it all.
    • CommentAuthorMike George
    • CommentTimeMar 9th 2013 edited
     
    Not really no. At least not easily. The way we used to form corners years ago was with timber 'rules'

    You would apply the first coat of render all over. Then nail a timber rule to the face of the wall around each window or at a corner. The reveals (or a side) would be rendered using the rule as a guide and allowed to harden.

    The rule was then removed and the main rendering applied on the wall face (or other side) The hard reveal acting as a guide. In this way a thickness of wet render is applied at the corner and this was then formed free hand with a plasterers float. Depending on the thickness this could be 'rounded' to some degree.

    In later years corner tools have become available though they are more appropriate for plaster finishes where the corner is already formed by backing render or plasterboard. I've never thought much of these though as the corner is weak compared to a bead.

    All of this applies to sand/cement/lime render. I haven't used much of the acrylics so don't know whether they *behave* in the same way.
  1.  
    example on one of the EWI thread last year of rounded corner
    • CommentAuthorShevek
    • CommentTimeMar 9th 2013
     
    Hmm, okay.

    So how small of a radius could we go to before we needed a bead do you think?

    Are you talking about this thread James?
    http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=9734
    • CommentAuthorShevek
    • CommentTimeMar 9th 2013
     
    Do you think we could get away with a 25 mm radius as shown in the jamb in this detail, by forming the radii in the insulation first?
  2.  
    A skilled plasterer could form such a corner freehand in sand/cement. I'm just not familiar enough with acrylics to say though sorry.
    • CommentAuthorTriassic
    • CommentTimeMar 9th 2013
     
    How about doing a test piece?

    What I was thinking, is why not use some hardboard pinned to the insulation as a base along which to run a router with a 25 mm radius cutter. I was thinking the hardboard should stop the router base digging into the insulation as you pass over it. Worth a try??
    •  
      CommentAuthorfostertom
    • CommentTimeMar 9th 2013 edited
     
    I should think very tricky because the thickness of the (thin) acrylic coat seems to be determined by the size of (some of) the aggregate, under the float - in other words there are relatively large lumps in there. Trying to freehand would, I should think, simply push the lumps off the corner - nightmare.
    • CommentAuthorNoodle
    • CommentTimeMar 14th 2013
     
    Does anyone know how "mikerummey" formed that very rounded corner in the thread that was linked to?

    Could you not cut a chamfer (say 45 degree angle) at the corner using a saw and then smooth out with render? Does anyone know how easy that would be with wood fibre board as opposed to others?
  3.  
    I'd prefer to make the profile on the insulant first, then render. Easy on phenolic, but a nightmare on wood-fibre, I would guess. It's hard enough to saw. I doubt it would take to rasping.
    • CommentAuthorShevek
    • CommentTimeMar 17th 2013
     
    • CommentAuthorShevek
    • CommentTimeSep 24th 2013 edited
     
    Baumit does "The Baumit KantenSchutz Flexibel is suitable for forming curved edges such as arches, rounded corners or similar."
    http://www.baumit.co.uk/dbfs.php?file=dbfs:/Prospekty/EWI_Accessories_Folder_engl.pdf

    Anyone used these?
    • CommentAuthorMikeRumney
    • CommentTimeSep 27th 2013 edited
     
    This is how I formed the bottom bead for the corners:
    1) Proprietory metal tray with section cut out and anti rodent mesh infill added (Pic from pre fixing of insulation)
    Renderer wanted more depth so ...
    2) Ditto plastic bead with alternate sections cut out to allow wrapping around
    (Last pic is scratch coat)
    • CommentAuthorShevek
    • CommentTimeJun 1st 2014
     
    Has anyone used Baumit's Flexbel corner bead? Could it be used to form a radius?

    Or could we simply run mesh continuously around corners?

    I also found the likes of these, a trowel for forming a radius corner:
    http://marshalltowntools.co.uk/5-x-3-1-2-bullnose-os-corner-trowel-durasoft-handle.html
    • CommentAuthorowlman
    • CommentTimeJun 1st 2014
     
    It's possible to get bullnose plastic corner beads for interior drywalling. Don't know how they'd fare for exterior use though.
    • CommentAuthordaserra
    • CommentTimeJun 2nd 2014 edited
     
    Posted By: MikeRumneyThis is how I formed the bottom bead for the corners:
    1) Proprietory metal tray with section cut out and anti rodent mesh infill added (Pic from pre fixing of insulation)
    Renderer wanted more depth so ...
    2) Ditto plastic bead with alternate sections cut out to allow wrapping around
    (Last pic is scratch coat)


    Lovely workmanship !
    • CommentAuthorShevek
    • CommentTimeJul 17th 2014 edited
     
    You know, Parex told me rounded corners (of the 25 mm park) shouldn't be a problem for a good applicator. Form the radius and simply run the mesh around.

    They did say to not to use a saw to form the curve as this could cut too much away; use a hot wire instead. But I would have thought a rasp would be the best way. Haven't had a good experience with hot knifing at least.

    Edit: just thought of a hitch though, for some reason I ordered the sills a bit shorter than the windows so although we have the insulation overlapping the windows by 25 mm the sills don't extend 25 mm into the insulation, so we'd end up with a strange little detail where the radius jambs meets the sill flashing. I can't for the life of me figure out why I ordered the sills slightly shorter than the windows.
    • CommentAuthorShevek
    • CommentTimeJul 18th 2014 edited
     
    Posted By: ShevekThey did say to not to use a saw to form the curve as this could cut too much away; use a hot wire instead. But I would have thought a rasp would be the best way. Haven't had a good experience with hot knifing at least.

    To get a nice radius we've found best way is to cut a number of facets with a snap-off knife and then sand it to get a smooth rounded corner.
    • CommentAuthorShevek
    • CommentTimeAug 22nd 2014
     
    Turned out okay, here's example of the base coat. It wasn't simple but it wasn't extremely difficult either. We wrapped the mash around the corners and used a 25 mm radius Marshalltown internal corner trowel. The main thing was getting the timing right; the render had to be dry enough to hold the mesh but wet enough to get a smooth finish without sticking to the trowel. When it came to the top coat I would oscillate around the corner in a circular kind of motion with the plastic trowel. (one mistake we made was doing the window jambs first in one spot; you really want to be doing it all continuously so you don't get a joint between dry and wet right on your radius).

    I''ll post a photo with the top coat when I get a chance.
    • CommentAuthorRobL
    • CommentTimeJan 7th 2019
     
    Hi Shevek - any chance of a piccy ?
    I do like the idea of rounded corners, it just seems "hard".
    • CommentAuthorowlman
    • CommentTimeJan 8th 2019
     
    Radius corner beads are available in plastic. They are generally used for drylining interiors I have no idea how you could adapt them for EWI
  4.  
    We have curved reveals and corners everywhere. In lime and clay. Both give you a lot of time, which helps. The underlying material is hempcrete or wood fibre or stainless steel mesh. It's quite easy to do the curves freehand. One trick is to use a straight trowel, kept perpendicular to the curve, but moved across the curve in a diagonal movement.
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