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    • CommentAuthorphil6000
    • CommentTime7 days ago
     
    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
    • CommentTime7 days ago
     
    vertical cedar cladding? or oak,
    •  
      CommentAuthordjh
    • CommentTime7 days ago
     
    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
    • CommentTime7 days ago
     
    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
    • CommentTime7 days ago
     
    • CommentAuthorCWatters
    • CommentTime5 days ago
     
    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
    • CommentTime4 days ago
     
    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
    • CommentTime3 days ago
     
    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
    • CommentTime3 days ago
     
    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
    • CommentTime1 day ago
     
    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
    • CommentTime1 day ago 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
    • CommentTime1 day ago
     
    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.
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