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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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    We are looking at EWI using polystyrene/silicone render on a wall, which the kids want to hit tennis balls and play footie against, it's the only one without windows.

    Question: how resiliant is eps/render to having tennis balls served at it?
    • CommentTimeJun 9th 2019
    My guess would be it'll be fine, as long as there's some fibre or mesh in the mix, but I don't know. Why not ask the supplier/manufacturer?
    • CommentAuthortony
    • CommentTimeJun 9th 2019
    No, a tennis ball or a football will be ok for a while unless hit very hard but repetition will cause the render to turn to powder and fall off. Once this happens the polystyrene will start to loose one bead at a time

    • CommentAuthortychwarel
    • CommentTimeJun 10th 2019
    This has always worried me, especially where you see render EWI on terraced houses right on the pavement, how long before the drunk yobs kick holes in it, or it gets hit by prams, pushchairs cars being parked on pavements etc.
    In my opinion in that situation you have to have a hard rigid outer skin (blockwork or brick)
    • CommentAuthorjamesingram
    • CommentTimeJun 10th 2019 edited
    my kids do so far no problems yet.
    I experimented on some about a decade ago , hitting it with a hammer , it damaged the grit pattern in the finish but didnt break the mesh or greatly misform it.
    unfortunately I cant say the same for my tin shed!
    • CommentAuthorgravelld
    • CommentTimeJun 10th 2019
    Always been a concern of mine. Take a look at:


    guide 2.

    Nothing conclusive as such, but maybe gives something of a framework to build your further research off.
    A couple of years back we had hail stones the size of tennis balls - no really - in places there were holes knocked in the thin film render where the top coat was knocked off exposing the mesh. But the same hail storm destroyed several asbestos/cement tiled roofs broke windscreens and dented car roofs and bonnets. Oh and the local shepherd was put into hospital after being struck on the head.

    The conclusion I have come to is that there is a bit of give and bounce to the EWI but repeated abuse will damage it. I wouldn't let the kids use it as a squash court!
    • CommentAuthorgyrogear
    • CommentTimeJun 10th 2019
    Posted By: jamesingramI experimented on some about a decade ago , hitting it with a hammer , it damaged the grit pattern in the finish but did [? NOT ?] break the mesh or greatly misform it.
    Thanks all,
    The BBA certs for several of the mesh/render systems certify them as "Category II' which is suitable for locations high enough up walls to 'limit the size of the impact' from 'throw or kicked objects'

    To be suitable for general public areas, they would have needed to be Category I.

    I am keen that the house is as much a workable home for the kids as it is for me, and that they get out and kick balls about like I did at that age, instead of festering inside posting on internet forums like I do now... If a wall construction cannot stand up to a game of wall tennis, then it's not fit for purpose AFAICS.

    On the plus side there must now be many EWI houses around Europe, lived in by many teenagers, and I haven't yet found actual reports of real damage from balls, thanks James and Peter.
    • CommentAuthorRobL
    • CommentTimeJun 11th 2019
    EWI suppliers can use different glass reinforcement meshes - typically there is extra mesh around windows & doors, and sometimes an extra layer of mesh at lower level where more impacts may happen. I think unless you specify extra mesh, just one layer will be used all over (except for diagonally at the corners of windows & doors to prevent movement cracks).

    I've heard of "Panzer" mesh, which is an example of coarse weave heavier duty mesh, I think used under the regular glass mesh for the heaviest impact area. When an EWI system is rated, there's talk of how many Joules impact the system can cope with. I'm not sure how that relates to regular tennis playing, other than a higher number being better. I've heard of 2Joules up to 50Joules - 50 from memory being demonstrated by a man hitting the EWI with a rubber mallet as hard as he could.
    Here's an example of the heavier duty mesh:

    Nb: I'm in the process of learning about all this for our house, but don't mistake me for an expert, I'm just a DIY-er.
    • CommentTimeJun 11th 2019 edited
    A tennis ball apparently is 57 g, call it 0.06 kg. The world record for a serve is apparently 263.4 kph, call it 75 m/s. So the kinetic energy is 0.5 x 0.06 x 75 x 75 = 168.75 Joule, call it 170 J.

    So don't invite Samuel Groth to play against your wall ! :bigsmile:

    edit: though as long as the ball bounces off with some speed, that presumably reduces the energy transmitted into the wall. Not sure about the impulse (is that the right term?).
    Er no, the damage is also related to the impact area which depends on the size and elasticity of the ball, not just the kinetic energy. Imagine a tennis ball, a golf ball and a 10mm steel bolt, all similar mass and struck at similar speed to give the same kinetic energy. We'd expect different damage! My kids will probably try all these...

    The energy levels RobL mentioned are related to tests with standard sizes of steel ball, defined in the ISO standard ISO7892 (see gravelld's link above). There are other tests using a standard size bag of glass marbles, swung with 100s of Joules. Unfortunately these results can't be directly related to tennis/foot/basketballs or neds with a hammer.

    Impulse is a vector showing a change of momentum m.deltaV = integral(-F.dt), so isnt related to energy which is a scalar (0.5m.v^2), different units and meaning, etc

    Groth is an Aussie, not sure if they have EWI down under.
    • CommentAuthorgyrogear
    • CommentTimeJun 11th 2019
    Sam Groth contra EWI wall
    anagrams to
    Oh Wow! Clatters Alarming

    Superb !!!
    • CommentAuthorborpin
    • CommentTimeJun 11th 2019
    Just hope they don't take up cricket.
    Archery is probably also off limits, as are darts and airgun target practice.

    But seriously, I did all these things against a brick wall as a kid, I'd be hypocritical to stop my kids! It must be possible to have an insulated equivalent that stands up to some rough treatment!
    • CommentTimeJun 12th 2019
    Posted By: WillInAberdeenIt must be possible to have an insulated equivalent that stands up to some rough treatment!

    Just build your insulated wall and add a suitable balanced, ventilated rainscreen.

    3' of reinforced concrete perhaps?
    Or maybe some corten steel?
    Or 10' of rubber?
    • CommentAuthorgravelld
    • CommentTimeJun 12th 2019
    You could always build a separate brick wall to kick a ball against?
    • CommentAuthorbhommels
    • CommentTimeJun 12th 2019
    9mm brick slips instead of thin render? The weatherby system with a metal mesh behind the slips looks fairly robust....
    • CommentAuthordathi
    • CommentTimeJun 12th 2019
    either buy them a tennis rebounder net or attach 8x4 sheet of plywood painted same color as wall to the wall. it only for few years till they grow out of it here in Ireland we have hurling the ball is 100 g with solid core so external insulation has no chance.
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