Ive built a brick and block cavity wall, plan is to foam-glue kingspan seconds to the inside for insulation.
But it has cracks and holes in some of the mortar, I want to stop any moisture and vapour getting through, so could plaster it or render it before glueing on the kingspan.
Maybe bonding plaster would be easiest? Or is there a reason to use sand and cement render?
advice please
George
Foil is the only thing that stops water vapour. Ties should keep the inner leaf stable, blockwork does tend to crack. Cavity fill is usually cheaper, easier.
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Any vapour barrier needs to be on the warm side of the insulation.
Richard
???
Kingspan has its own foil coating. Just use the foil tape to cover any gaps that are left that you filled with expanding foam....
If you are worried about damp from outside, that's what the cavity is for. |It does have 'airbricks' I hope?
Indeed. For an agricultural timber frame building I used *distance screws* to secure laths over the foam insulation for exterior boarding. You could then secure your plasterboard to the laths with conventional screws. The tricky bit would be drilling your brick/block for the screw plug through the lath and final assembly.
In an earlier discussion TNP suggested fixing treated timber to the wall to take the screws. Something more durable than timber might be needed for an exterior blockwork wall.
None o f this is actually necessary with kingspan as you can get it with plasterboard attached and use foam dot and dab to stick it to the brickwork. In the end that might be cheaper than using seconds.
With foam all you need to do is hold it in place and evenly mounted and use dots of foam and then it will end up with a small air and foam gap behind it, which is fine. The plasterboard then - if its separate - goes on with more dots and dabs of foam glue
Render it with 4:1 sand & cement Will fills holes & voids. As you are then adding foam sheet all you need do is rule it off with a straight edge.
If you want to help you can add waterproofer to the mix ... but inner leaf of a cavity wall should not get wet.
Waterproofer in the mix on the cold side of insulation is exactly where you don't want it. Any water that gets though to the brick/blockwork needs to then dissipate outwards gradually.
A wrote:> Waterproofer in the mix on the cold side of insulation is exactly where you don't want it. Any water that gets though to the brick/blockwork needs to then dissipate outwards gradually.
... But if i seal the top of the kingspan with EDPM, and its foiled on the warm inside, the only place water can get in is through holes in the blockwork, so if i smooth it over with mortar where there are small holes in the pointing then no water will get in. Better than leaving the small holes surely?
[g]
If you could put that in terms that aren't too vague to carry meaning we could get somewhere.
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