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Green Building Bible, Fourth Edition
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    • CommentAuthorMarkyP
    • CommentTimeMar 9th 2016
    I'm in the depths of planning my extension and renovation. I've got EWI specified over both the existing (badly insulated) cavtiy walls and over the new walls on the extension. I'm going to be self-managing the work and likely fixing the graphite EPS EWI myself and then having a contractor apply a lime render finish. I'm thinking about the possibility that I end up taking a while to do the EWI (leaving some exposed while finishing the remainder) or there's a gap between it being fixed and the render being applied. I've read that EPS doesn't like UV, would a period of exposure to sunlight (a lot of wall facing SW in full sun) cause any issues? Just factoring in what I would need to do if the exposure period ran beyond days into weeks.

    A possible solution I thought of would be to use a roofing membrane or polythene sheeting and temporarily batten fix that over the EWI and then remove prior to rendering. Or am I worrying about nothing?
    • CommentTimeMar 9th 2016
    Especially the black EPS, before rendering, can easily get too hot in odd places, under strong sun, and it starts collapsing into itself. The greenhouse next door focussed enough sun to completely destroy a couple of sq ft! Polythene wrapped packs are susceptible. Prob not same risk with more reflective white EPS.

    But that's not UV degradation.
    • CommentAuthorMarkyP
    • CommentTimeMar 9th 2016
    it's not UV degradation but it's another worry for the list!
    • CommentTimeMar 9th 2016
    I've had some left over graphite EPS in the garden for a year or so now. The main degradation that I can see is green colouration due to stuff growing on it. Apart from knocked off corners etc mainly sustained when the sheets made a bid for freedom during one of the gales. Some of it was exposed the whole time, and some was still in the white polythene-wrapped packs for most of the time.

    I haven't seen any visible damage caused by thermal effects or by UV, but maybe there are invisible effects? The only time I saw shrinkage was when I tried burning a piece, but it really doesn't want to burn although it can be made to.

    MarkyP, what's your structure for the new walls? Will it cope with moisture?
    • CommentAuthorbxman
    • CommentTimeMar 9th 2016
    I do not think it wants to be un covered for any longer than necessary.

    and not sure lime render would have the strength to bind the fiberglass mesh

    or have you had expert advise to say it is feasible ?
    • CommentAuthorMarkyP
    • CommentTimeMar 9th 2016
    <blockquote><cite>Posted By: djh</cite>

    MarkyP, what's your structure for the new walls? Will it cope with moisture?</blockquote>

    aggregate blockwork.
    • CommentAuthorMarkyP
    • CommentTimeMar 9th 2016
    <blockquote><cite>Posted By: bxman</cite>I do not think it wants to be un covered for any longer than necessary.

    and not sure lime render would have the strength to bind the fiberglass mesh

    or have you had expert advise to say it is feasible ?</blockquote>

    I think I'll probably play it safe and cover it if it's going to be exposed for more than a few days. Especially if there's a chance of full sun. I would imagine I could get the S and SW face covered with some sheeting in half a day. I could probably even just tack something to the eaves and weight it down at ground level to provide a screen.

    render - not 100% sure yet. Lime Green have a BBA for their lime render backing and top coats over EPS. http://www.bbacerts.co.uk/CertificateFiles/51/5173ps1i1.pdf
    I've left some exposed for about 6 months and surface degraded a bit and went dusty
    Some installers suggest rasping it prior to render coat to improve key , which i did in this case
    and it removed surface problems
    As to direct sun, ive had boards melt up a little just sitting outside on a hot day on top of the pile as Tom mentioned
    • CommentTimeMar 9th 2016
    Looks like I was lucky with my pieces!

    Posted By: MarkyPLime Green have a BBA for their lime render backing and top coats over EPS

    That's interesting to see. I note that it stresses the system must only be applied by people who have been on their training course. I'm not sure if that would affect any warranties or whatever? I'm also a bit surprised that the maintenance instructions don't say anything about painting the lime, but I suppose the finish coats must deal with that.
    • CommentAuthorMarkyP
    • CommentTimeMar 10th 2016
    I'll have to forego the warranty, certainly. But reckon if I source and fit the EPS and get one of the local renderers/ plasterers who work with lime (we have about few doing conservation work) then I reckon it should come in a great deal cheaper than a trained specialist firm fitting it all as system with warranty. I don’t see too much risk with lack of warranty provided ofcourse I use the right materials and methods and find a decent renderer. I used to do a bit of plastering myself, if I had more time I'd probably have a go at the rendering. I did consider making a test wall by fixing a sheet or two of ply on some fence posts and then the EPS and mesh and see what the LG mix is like to work with. Realistically I just don’t have the time for that which is shame.
    • CommentTimeMar 10th 2016
    Why lime exactly, in this case? Once accepting to use EPS rather than idealogical wood fibre, what's wrong with the ordinary acrylic patent render, thin-coat, little enough of it?
    • CommentAuthorMarkyP
    • CommentTimeMar 10th 2016
    a few reasons. An expectation that it will be less likely to go green. Prospects of finding a contractor - there are plenty of one man bands doing conservation lime work in my area. Not had so much luck finding someone who'd do the same with acrylic or silicone other than specialist outfits that want to sell and install a full system. I like the lime finish over some of the acrylic renders I've seen locally, and prospects for limewash to colour change later if the fancy took.
    • CommentAuthorbxman
    • CommentTimeMar 11th 2016
    I think you will find that the plasterers doing most of the EWI work are not employees of the Companies doing the jobs .

    If you were to find any work being done and approached individuals doing the plasterwork they would be willing to do yours I suspect by the same token anyone with the skill to do line would not find any problems using the other materials .

    you can but ask or have you already done so ?
    • CommentTimeMar 11th 2016
    Any plasterer can tackle EWI acrylic render - it's not that different from other kinds of patent render, widespread.
    • CommentAuthorMarkyP
    • CommentTimeMar 11th 2016
    the few plasterers I know havent used it (acrylic). Should think the only thing to swing me toward acrylic/silicone would be budget (looks a chunk cheaper material cost per metre). Will start with lime and see as its preferred for reasons above.
    The stuff I have used smells like emulsion paint on heat. It strips the hairs out of your nostrils! I would much rather use lime, for all its corrosive characteristics - It don't smell bad!
    • CommentAuthorjamesingram
    • CommentTimeMar 13th 2016 edited
    If you've capable of doing a bit of plastering youd be fine. I cant plaster but happily do ewi mesh rendering. ( though I'm not fast) its considerably more forgiving. Render for the unskilled I call it.
    Not sure of your location but there's a guy on ebay doing all-in materials 100mm for 16m2, for silicon
    he can get thicker stuff ..I got some 150mm of him recently. Check southern insulations supplies or pm me
    It you want a quick 'how to' guide let me know and I post one up.

    That would be really useful for me - I have to do a couple of bits of EPS EWI later in the year. Details on how you treated (or insulated over) the dpc would also be appreciated. I am minded to simply insulate over, as discussed on several threads previously.

    Can you whisper me supplier details too, please?


    • CommentAuthorMarkyP
    • CommentTimeMar 14th 2016
    If you wouldn't mind please PM me that supplier. I had a look but not sure I've found the right place. I'm in the south east.

    I had a look on youtube, found a video from weatherby building systems showing their system of two base coats and silicone over EPS. Seems straight forward enough. MY place is a bunglow and so each hit is a fairly manageable size, you might have persuaded me to to give it a try.
    • CommentAuthorjamesingram
    • CommentTimeMar 15th 2016 edited
    prep wall , remove all loose etc
    fixing boards:
    Good flat wall (adhesive/mesh coat render)
    cover board 50% with wettish mix 25mm deep in 100mm strip
    use deep notched trowel to spread board
    spread wall the deep notched trowel ( for good external airtightness layer)
    Press board onto wall, tap and bed in level with bit of flat 2/3 and shunt up to others much like wall tiling
    2 fixings per board or part board
    Uneven wall/ rough cast
    foam up board in strips and round edge ( to stop air movement behind boards)
    push on wall
    2 fixings per board
    once dry, rasp up any protruding areas and foam gaps and joints
    Mesh coat
    tight trowel a coat to wall , trowel in mesh in horizantal stips as long as possible
    the mesh flattens it up and pretty much does most the work for you as you work it in
    I use a long tapping knife to float mesh in. sometime this is enough , dont worry if a little mesh appear to be
    showing behind render as top coat will cover this. the trick is not to put too much on.
    If you do and or its going a bit pear shaped leave it to dry a bit till its skinned up a bit and harder
    then wet sponge it in circle motions, like up would sand cement render.
    Let dry then primer , get a got coverage otherwise grey may grin through.
    Top coat
    dont do it if its likely to rain or below 5 deg or in direct hot sun light , best is a cloudy mild day.
    mask up , use window reveal trims, small drip bead and corner mesh beads , lay a clean plastic sheet below work area (you lose a bit of gear off your hawk as it a bit wet so this lets you recover some)
    again trowel on tight as possible, with hawk and trowel, it very temperature sensitive and you need to finish float it whilst still wet, so do a small 3m2 then finish float, keep a wet edge , if you can get 2 guys one can trowel the other float then switch occasionally , no tea breaks mid elevation, you need to do full elevation each hit.
    finish float get a special plastic trowel/float and just run over in quick flat circular motions to remove trowel lines.
    the grit in it gives you the thickness and can also fill the odd hole in the mesh coat. again keep it thin.
    brush in tight details, do reveals after but keep corner wet it possible
    Do NOT touch finish once drying or go back over area.

    Below dpc i normally just run EPS down to ground or below but put a drip bead in at dpc for looks then paint below with black. french drain with pea shingle is advisable if going up against it.

    pm'd info chaps
    Many thanks James. Much appreciated.
    • CommentAuthorMarkyP
    • CommentTimeMar 16th 2016
    thanks for the PM and the method write up.
    • CommentAuthorSilky
    • CommentTimeJul 1st 2020
    "Below dpc i normally just run EPS down to ground or below but put a drip bead in at dpc for looks then paint below with black. " - can anyone tell me what the 'black' is? Bitumen coating?
    System providers sell a black (or black-ish) version of the 'gritty finish' for under-dpc/underground use. Often called 'mosaic finish'.

    It goes on top of either standard or 'special underground' base coat - depends on your supplier.

    https://ewistore.co.uk/shop/ewi-050-acrylic-mosaic-render-25kg/. Sit down before you look at the price. (It obviously comes in many more colours than I remember).
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