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Posted By: mikaelHowever after I started, I found that the PU foam shrinks when it cools and can cause significant damage to the masonry. BASF walltite seems a bit worse than other foams, which I also tried.
Posted By: delpradoAlthough my real dream is actually some sort of old looking house, maybe stone with a thatched roof, but passiv...
Posted By: djhPosted By: mikaelHowever after I started, I found that the PU foam shrinks when it cools and can cause significant damage to the masonry. BASF walltite seems a bit worse than other foams, which I also tried.
That seems like a fairly fundamental indictment of both the BASF product and the BBA quality assurance process. What do BASF have to say about your problem?
Posted By: gravelldOff the topic of wall ties but...
Walltite is advertised for use in hard to treat cavities though. Surely they would've had trouble before?
There's also Retrofoam and... icynene?
Posted By: mikaelI am looking into getting this to construct a roof by fully filling the voids between and through open web joists used as rafters.
Posted By: mikaelPosted By: djhPosted By: mikaelHowever after I started, I found that the PU foam shrinks when it cools and can cause significant damage to the masonry. BASF walltite seems a bit worse than other foams, which I also tried.
That seems like a fairly fundamental indictment of both the BASF product and the BBA quality assurance process. What do BASF have to say about your problem?
Good question. I took it up with BASF and Isothane (both have had issues). They either blame the installer not installing it right, or just bad luck. Isothane said that if you install it right you don't get any issues. However I believe BASF have had legal action taken against them in Ireland. BASF also visited my site and checked a foam sample coming from the installers equipment and they said it was good. I have also contacted the BBA and they don't seem to wish to discuss exactly what testing they did.
Posted By: djhHmmm... I think it depends on who the risk is shifted to. It seems to be ok for manufacturers to scream "caveat emptor", backed by testing regimes in which we continue to see issues.But I think 'caveat emptor' applies just as much to building techniques as it does to property purchase.
Posted By: tonythe vapour barrier on the cold side of the insulation and can only see this leading to problems
Posted By: TimSmallThanks for the interesting comments and photos mikael. I suppose with a 300mm cavity you'll have about 4x the total shrinkage (at least - more if thermal effects are greater due to the centre reaching higher temperatures) vs a 75mm retrofit cavity.
Was all the pouring done from the top? What height of foam did you fill in each foam "lift"? How long between the masonry being completed?
I think I'd be a bit cautious about using phenolic due to water absorption? Not that I know much about it - just that Kingspan Kooltherm acts like a sponge (as does the green foam that florists use to stick flower stems in - because it keeps the flowers well watered - which is also phenolic), but perhaps this can be overcome with different phenolic foam types or additives?
With a 300mm cavity, did you consider using rigid PIR boards instead of polythene sheet against the outer (or inner) face (e.g. 200mm PIR boards, and 100mm insitu foam)? Since the in-situ foam would then stop the thermal bypass which is the main drawback of PIR-in-cavity-wall.
Only makes sense if PIR board is cheaper per unit volume than the foam I suppose, but would get you a slightly higher U value for a given wall thickness ("mid life" λ value for a full sheet PIR 0.023 W/m²·K, and long term λ value of 0.026 vs. 0.029 W/m²·K for the insitu foam).
Graphite EPS, or even mineral wool would also be worth considering I suppose?
Posted By: TimSmallI think I'd put in something other than polythene on the outer face (e.g. EPS or mineral wool) as a vapour open debonding layer.
Posted By: TimSmallInteresting to hear that you've managed to get the in-situ foam cheaper per unit volume than PIR board. When I've had quotes for it in the past, it's always worked out more expensive per unit volume.
I would have thought that the in-situ foam would seal up any gaps between PIR boards?
I think I'd put in something other than polythene on the outer face (e.g. EPS or mineral wool) as a vapour open debonding layer.
Posted By: mikaelI am not too concerned about the polythene used as the debonding layer as the foam is pretty much impermeable anyway, so facing it with another impermeable layer should not cause a problem.
Posted By: TimSmallPosted By: mikaelI am not too concerned about the polythene used as the debonding layer as the foam is pretty much impermeable anyway, so facing it with another impermeable layer should not cause a problem.
I don't think that's right - the µ value (water vapour diffusion resistance) of polyurethane foams is around 30 to 200 depending on the composition (60 is often quoted).
The µ value of polythene DPC membranes are around 100000.
For comparison most timbers have a µ value of about 20 to 50.
I've seen fully saturated polyurethane foam insulation boards taken off an old "warm roof", and I've also seen wufi simulation results for green roofs where the polyurethane slowly fills up with water from the top down (over several years).
Water vapour diffuses more quickly at higher temperatures, and this can result in moisture "piling up" on the cold side if there is a high resistance layer on the outside.
Because absolute humidity is nearly always higher inside a home in the UK climate, it would be safer to use something which is relatively more vapour open on the cold side of the cavity.
e.g.
PIR foam µ = 60
EPS µ = 60
mineral wool µ = 1
Bricks and blocks have µ between about 10 and 150