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    • CommentAuthorphil6000
    • CommentTimeJun 16th 2017
     
    A couple of years ago we built an extension with an oak frame. Most panels were glazed but a few were 'filled in' as we wanted a bit more privacy in bedrooms and a bit less glass. The panels were made of 25mm Malaysian marine ply to EN636-3 and painted with textured masonry paint to match the render that is next to the oak frame.

    The ply has not weathered well and has hairline cracks and some small splits and is worst on the panels that face south-west. The suppliers said it was my fault for painting them-not sure if this is true.

    I'm now looking for a way to protect the panels from further sun and rain damage, but without causing other problems. I was told that there are cement based cladding boards that would work but after ringing various manufacturers technical depts none will say their product is suitable, even though I suspect some are. I think the issue is breathability. Can anyone suggest a product, ideally no thicker than 8mm and paintable, or another solution?

    Most panels are about 2.4m x 0.65m, and there are battens secured to the back to take the internal plasterboard, with insulation and a vapour barrier in between. The boards are clamped to the oak frame by the coverboards and gaskets, just like the glazing units. The option of ripping them out and starting again is not one I want to contemplate at the moment.

    Any help and advice will be greatly appreciated. Thanks.

    Phil
    • CommentAuthortony
    • CommentTimeJun 16th 2017
     
    vertical cedar cladding? or oak,
    •  
      CommentAuthordjh
    • CommentTimeJun 16th 2017
     
    Posted By: phil6000after ringing various manufacturers technical depts none will say their product is suitable, even though I suspect some are. I think the issue is breathability.

    That's a bit vague. Have you tried writing to them to ask? What exactly were you proposing anyway?
    • CommentAuthorphil6000
    • CommentTimeJun 17th 2017
     
    I have been told sheet materials such as Cemberit Viroc or Sunflex,Marley Eternit, Rockpanel Ply and others could be attached to the front of the existing marine ply, within the rebate formed by the oak coverboards. This would keep the sun and rain off the plywood and could hopefully be painted to match the render on the rest of the extension.

    The issues seemed to be whether the edges should be sealed to prevent damp getting behind it (and onto the existing plywood) and whether moisture coming from inside could escape. The sheet could be attached (screwed or glued?)with or without a thin air gap and I don't know enough to predict what the implications of the various options-and this is where 'technical' won't comment.

    Hope this helps to explain the issue.
    • CommentAuthorowlman
    • CommentTimeJun 17th 2017
     
    • CommentAuthorCWatters
    • CommentTimeJun 18th 2017
     
    WBP plywood varies enormously. Near the end of my job I ran and got a few sheets from a different source. That looked identical but delaminated before I could get it covered up. Don't know how they had the nerve to call it waterproof.

    If you fit something over the existing board will it be possible to stop water getting to the original board?
    • CommentAuthorgoodevans
    • CommentTimeJun 19th 2017
     
    All the standard cladding will want ventilation behind so you will exceed your 12mm limit. I'm sorry I don't have a solution - but just fixing something flush to the existing surface may not behave well.
    • CommentAuthorphil6000
    • CommentTimeJun 20th 2017
     
    Thanks for the replies so far. In response;-

    owlman-thanks for that. In fact looking more closely I can accommodate a 12mm thick product-but see below

    CWatters-I can seal all around the edges of a board which will presumably prevent rainwater reaching the surface of the plywood beneath-but does the plywood need to 'breathe'-in which case should I leave an air gap somewhere (at the bottom, for instance)

    goodevans-as I've said to owlman I now realise I can put a 12 mm sheet in the space, and even a small air gap too. I had looked at boards as thin as 6mm and I guess from a weight point of view, the thinner the better. Could you explain what you mean by 'not behave well' please as this is, I think, at the heart of the problem.
    • CommentAuthorgoodevans
    • CommentTimeJun 21st 2017
     
    The difficulty I think is that you have to assume that rain or other liquid water will somtimes get past the rain screen - with a ventilation space behind the water can run/evaporate away allowing the cladding and the surface behind to dry in a reasonable time. Even if cladding is 'breathable' it won't breath enough for any liquid water ingress to dry. Even though you won't plan for water to get past the rain screen it will occasionally or at some time in the future.

    In short: design to keep the water out, but in case it gets in, design to allow it to get out.
    • CommentAuthorphil6000
    • CommentTimeJun 22nd 2017
     
    Thank you goodevans. I think I am now getting somewhere!

    I understand what you are saying but can I ask about a couple of practicalities ie how deep should the air gap between the two surfaces be and how do i achieve it ie what sort of spacer material?

    As the new surface sheeting will be in a rebate on all four sides is it sensible to seal the top and sides with silicon and leave a few mm gap at the bottom to allow any moisture to drain/evaporate?

    What qualities should I look for in the new cladding and does painting it prevent it from breathing?

    Should the proposed plan prevent the plywood from deteriorating further and is there something I should do to it before I cover it up?

    Sorry to be a pain but as I was blamed for causing the present problem (even though I'm not fully convinced I was guilty) I am anxious not to repeat my alleged mistakes.
    • CommentAuthorgoodevans
    • CommentTimeJun 22nd 2017 edited
     
    I'm out of my depth here - but I would say leave a gap top and bottom as a minimum and allow the air behind to be drawn up. Alternatively leaving a 25mm even gap all around the cladding may look good - think shadow gap like velfac windows (but the creepy crawlies can live there - eaves mesh may limit their movement).

    The larger the air gap behind the better the ventilation - but any gap will work particularly if the sun heats up the cladding - drawing cold air at the bottom and releasing it warm at the top. You'll get no guarantees however.

    Any rain or other moisture that gets through the gaps will evaporate away. Make good the surface behind - it would still be your 'waterproof' layer - but it would be protected from the sun and rain by the cladding.

    You have little to loose here - the only other solution is to remove the panels - so think of this as a final attempt to have a good looking rain-guard protecting the less than ideal structure behind.
    •  
      CommentAuthordjh
    • CommentTimeJun 22nd 2017
     
    Posted By: phil6000I understand what you are saying but can I ask about a couple of practicalities ie how deep should the air gap between the two surfaces be and how do i achieve it ie what sort of spacer material?

    As the new surface sheeting will be in a rebate on all four sides is it sensible to seal the top and sides with silicon and leave a few mm gap at the bottom to allow any moisture to drain/evaporate?

    It's usual to allow an airgap of 1" or so; a so-called ventilated space. Vertical battens are usual, commonly made of treated timber. Drainage just requires a gap at the bottom and doesn't require any significant gap, two adjacent membranes would suffice. Evaporation however is strongly encouraged by air flow so requires a significant gap and openings both at the bottom and at the top. The gap at the top will preferably have a cover to deflect rain.

    What qualities should I look for in the new cladding and does painting it prevent it from breathing?

    The new cladding should not be susceptible to rot (i.e. mineral rather than organic). Some types of paint stop the passage of water vapour whilst others allow it so it is very important to choose one of the correct type.


    Should the proposed plan prevent the plywood from deteriorating further and is there something I should do to it before I cover it up?

    Depends on exactly what it has been painted with and exactly how it is covered up.
    • CommentAuthorphil6000
    • CommentTimeJun 25th 2017
     
    Many thanks to goodevans and djh for your replies. I've attached a photo which I hope show the arrangement that I am trying to work round. I don't have the option of a deep ventilation space behind the board, and a big gap round either the sides or the top will, I think, allow more rain in than than let moist air out (particularly at the top where I think the rain will drip down the oak coverboard and blow in behind unless I can fit a rain deflector as djh suggests).

    I could probably put a 10-12mm gap behind a 6-8mm board without it looking too different to the glass panels-do you think that will allow for the evaporation needed, without it being perfect? I just want to try and protect the plywood underneath from further moisture or sun damage.

    djh-I note what you say about the new board being mineral based. I painted the plywood with masonry paint, which was presumably not breathable. I could try to sand most of it off and put something else on before I cover it with the new boards if it would be worthwhile in terms of long term preservation? There are 10 panels (9 on the first floor or in the gable above) to protect so it would be quite a big job and may damage further the top surface which is cracking in places.

    Any advice would be appreciated.

    Thanks

    Phil
      IMG_3328 (Medium).JPG
  1.  
    Posted By: phil6000A couple of years ago we built an extension with an oak frame. Most panels were glazed but a few were 'filled in' as we wanted a bit more privacy in bedrooms and a bit less glass

    A bit late to this party but for my tuppence worth - presumably the panels that were glazed were/are successful. Can you replace the troublesome ply panels with glass and then paint the glass internally. If painted black first then any colour of your choice you should get no light through, if you paint with a light colour only then some light will show.
    •  
      CommentAuthordjh
    • CommentTimeJun 26th 2017
     
    Posted By: phil6000I painted the plywood with masonry paint, which was presumably not breathable.

    Some are, some aren't, so it depends exactly what product you used.

    The ply has not weathered well and has hairline cracks and some small splits and is worst on the panels that face south-west. The suppliers said it was my fault for painting them-not sure if this is true.

    A photo showing the damage would be very helpful.

    I'm wondering if an alternative strategy is worth considering. Presumably the panels are fairly dry now with it being summer, so maybe it would work to get a thin mineral board and glue it on the front and then paint that. Hopefully that would slow down the damage enough to make the whole thing last for a good while until it finally needed more serious repair.
    • CommentAuthorphil6000
    • CommentTimeJun 28th 2017
     
    To Peter in Hungary-Yes the glazed panels are successful and if all else fails I could replace the wood panels with glass and then look at how to limit the light through it. I gather there is now fancy glass that will darken automatically -but to replace all the panels with glass will have many implications that I'd rather not consider right now.

    To djh-the masonry paint I used was Leyland Trugard fine textured masonry, and I can remember checking that it was suitable for wood and maybe that meant that it was breathable but I can't see whether it is now on Leyland's website and either way it seems to have failed.

    I've put up a picture showing the worst panel, taken today after the rain. I'd be quite happy to do as you suggest if it will work. As I've said before I just want to protect the existing damaged surface and don't know whether the existing panels need to stay breathable and therefore need a ventilation gap (does the house 'breathe' through those panels or does the fact that there is a membrane next to the plasterboard on the inside mean no moisture passes out from the house through the panels?)

    I'll also put up a photo showing the whole SW elevation on my next post.

    Thanks for your ongoing interest and help.
      IMG_3336 (Medium).JPG
    • CommentAuthorphil6000
    • CommentTimeJun 28th 2017
     
    Here is the South West side of the extension showing 5 of the panels.
      IMG_3325 (Medium).JPG
    • CommentAuthorowlman
    • CommentTimeJun 28th 2017
     
    For specialist paints this company have a good range. Speak to the right guy and you'll get good advice.
    I have no connection with them except I've used them in the past.

    http://holmanpaints.co.uk/49-paints-coatings-for-exterior-walls
    • CommentAuthorTimber
    • CommentTimeJul 1st 2017
     
    Looking at the pictures, I can almost guarantee you that wasn't marine plywood. My reason for saying that is that the ripples look like a thin decorative surface veneer that has started to delaminate from the rest of ply. BS1088 which is the marine plywood standard does not permit the use of thin surface veneers.

    Also if it was Marine to BS EN 636-3 (as you stated in the OP) then that is not the marine plywood standard. BS 1088 is.

    Good quality marine plywood painted with a breathable paint would probably fair OK. Its not a great design to be honest with you, but I think the problems you show are more to do with poor quality plywood.

    Not sure what to suggest in order to keep the existing panels, is removal and replacement a viable option? If so then proper actual BS1088 marine or even something like Tricoya would probably work OK, although a vented space between the cladding panel and whatever is behind would be best practice to help allow the plywood to dry quickly and evenly after wetting.
    • CommentAuthorphil6000
    • CommentTimeJul 2nd 2017
     
    Hi Timber. Thanks for your information. Maybe my description of 'marine ply' is wrong but it was definitely plywood to EN 636-3 which I believed was the best grade of plywood for exterior conditions (now I'm not so sure but when I complained to the suppliers I was told I had caused the problem by painting it)

    If I remove the panels I have to remove the oak coverboards, the fascia and soffits, the insulation, the vapour barrier and plasterboard on the inside. All this for ten panels right up to the apex of the roof-so I am very keen not to remove but to find a solution that leaves the boards in place and protects them from further damage.

    You mention a vented space behind a cladding panel and this seems to be the main issue, and one that I am still trying to get an answer to, ie how deep, how to create, how to prevent water from getting behind from above or the sides. Can you help?
  2.  
    About 3 years ago (I think) I painted, if that is the right word, some OSB with some leftover thin film acrylic render as used with EWI. The place faces north and has no overhang protection but to date there is no degeneration in the finish. The thin film acrylic render is flexible and breathable so it might be worth considering as a fix, and of course lots of colour choice.
    • CommentAuthorphil6000
    • CommentTimeJul 4th 2017
     
    Thanks, Peter in Hungary, for your comments. I know nothing about thin film acrylic render and a quick google for an Atlas product (Polish?) did not mention wood as a substrate, and applying it with a trowel. I like the idea of 'painting' on a product that will preserve the ply as that should be a whole lot easier than a sheet material on top-but I'm wary of applying a product I know nothing about to something that is already failing. Does anyone else have any experience of this product, or any other ideas?

    I'd also still appreciate some guidance on ventilation gaps if I go with some sort of thin mineral board on top of the plywood panels. Please.....!
  3.  
    You are right, the thin film acrylic render does not mention wood as a substrate, it designed for EWI systems. But it is flexible and breathable and over here the builders use the buckets that it comes in as cheap available buckets but you have to wash them out immediately they are empty otherwise they can not be cleaned - I say this as an indication of how well the stuff sticks!

    What I would do in your position is to wire brush the loose paint off (e.g. a wire brush on an angle grinder) and then paint or trowel on the render. If it did fail some years down the line then you are no worse off than you are today and as I said what I put up some time back on to OSB and it shows no sign of deterioration.
    • CommentAuthorgoodevans
    • CommentTimeJul 5th 2017 edited
     
    Peter, is acrylic render breathable - this link suggests not

    http://ewistore.co.uk/acrylic-render-vs-mineral-render-vs-silicone-silicate-render/

    If this is the case then the silicon render will do the job (but breathability may not be necessary if a waterproof coating will do the job) It's so difficult to visualise what water and/or water vapour will do.
  4.  
    The acrylic render over here is sold as breathable.
    • CommentAuthorphil6000
    • CommentTimeJul 16th 2017
     
    Thanks Peter in Hungary and goodevans for your comments. I have since been looking at acrylic renders, and spoken to a supplier of EWI products (as they are completely new to me). They confirm that the acrylic render is not breathable or flexible and recommended silicon render, but it cannot be painted on as it needs to be about 5mm thick. He said the only paint-on product they sold was silicon paint, which he said would give a 'level of protection'.
    It got me thinking whether there were any other, better, paintable products as they seem to get round the issue of ventilation gaps that seem to prevent me from finding a workable solution-presumably provided that they were breathable/flexible?

    I still don't know how important 'breathability' is. If there is a vapour barrier behind the plasterboard on the inner skin of these panels am I right in thinking that the only thing that needs to breathe is the plywood and anything I put on top of it? And if the top surface (whether paint or another panel) is waterproof does the plywood underneath still need to be able to breathe?
  5.  
    I may be talking out of turn here, but are there any techniques you can borrow from old timber framing?

    Lime render, which would be breathable?
    • CommentAuthorgoodevans
    • CommentTimeJul 17th 2017
     
    Phil - The silicone paint should be flexible to prevent re-cracking and waterproof and breathable - it would probably do what is needed and would be an ideal candidate for the job - and would not make things worse.

    The question would be can the existing surface me made flat enough (or is the paint thick enough) to create a good surface finish and would a smooth mat surface match the property. You've not much to loose if it does not work.

    I stress again I'm not an expert - and I have no experience - as you have small individual panels I'd have a crack of trying a thin coat render applied directly to that base - you'll get no guarantees - but as long as it sticks to the existing the finish is up to the skill of the person applying (practice on another board perhaps). It will only be 1-3mm thick.
  6.  
    Phil6000, I think the product that the EWI suppliers were talking about is not the same as that which I have been using.

    The product I have been using is Ceresit CT 60. From the manufactures web site

    CT 60 Acrylic plaster, structure like stone with grain 1.5 mm, 2.0 mm or 2.5 mm
    Properties

    Resistant to weather conditions with low absorbability and high elasticity
    Vapour permeable and resistant to damage
    BioProtect formula – resistant to the development of fungus, algae and mould
    Possibility of the machine application*
    Available in full palette of Ceresit Colours of Nature®

    And

    Ceresit CT 60 is used for making thin-layer plasters on concrete substrates, traditional plasters, gypsum substrates and chipboards, gypsum cardboards, etc

    It also says to apply at the thickness of the grain, hence the usefulness of using a float to apply and for the one I was using this gives a thickness of 1.5mm.
    • CommentAuthorphil6000
    • CommentTimeJul 21st 2017
     
    Thanks again Peter in Hungary and goodevans.I now feel I am getting somewhere and am happy to abandon the idea of another board on top of my plywood boards. I've started to look at Ceresit and it looks promising.

    Peter did you say it was the CT60 that you applied by painting rather than by float? What sort of finish did you get? I originally wanted a masonry effect finish which was why I used textured paint, so if the CT60 when applied by brush looks similar that will be good. Also you suggested I remove the existing paint finish-was that just the loose stuff or all of it. It is actually adhered quite well and it is more the top surface of the ply that seems damaged in places (and really pretty good on the East side of the house) so I'm wondering if it should be removed or if the render will just go on and seal/cover the lot?

    Thanks in anticipation.
   
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