Impact of losp treated timber on polystyrene claddings
Impact of LOSP Treated Timber on Polystyrene Claddings
Background With the increased use of LOSP treated framing, questions have been raised about the effect of fixing polystyrene claddings onto treated framing. This trial was set up by Osmose to determine whether there were any adverse effects from fixing polystyrene claddings onto LOSP treated framing. Trial Outline Samples of 90 x 45 KD rougher headed radiata pine were treated in the LOSP plant at Ahead Lumber, Pokeno. The wood samples were placed on top of commercially treated packets of timber. One set of samples was treated using the orange-dyed, H1 PLUS formulation (containing IPBC, permethrin and water repellents in Exxon Mobil Pegasol 3035 solvent) and the other was treated with green dyed H3 export fluid (containing permethrin, tributyl tin naphthenate and water repellents in the same solvent). Within 24 hours, one set of treated wood samples were placed on top of the polystyrene cladding supplied by James Hardie. Samples of building wrap (Gib FrameGuard and JH Protek) were placed such that they separated some of the wood samples from the cladding. After a further 5 days, a second set of wood samples was placed onto building wrap and the cladding. This delay was to simulate a normal, minimal amount of drying prior to a building being clad. The samples were maintained in an air-conditioned building at approximately 20ºC for this trial. Observations There was significant attack of the polystyrene where it was in contact with the 24 hour-old H1 PLUS samples. This consisted of a col apse of the expanded polystyrene between 6 and 11 mm in depth. There was also significant transfer of the orange dye to the polystyrene and wrap. (see figure 1).
Figure 1: Polystyrene in contact with 24-hour old H1 PLUS LOSP
There was only very minor pitting where the 24 hour-old H3 LOSP treated timber was in contact, and little or no dye transfer (Figure 2).
Figure 2: Polystyrene in contact with 24-hour old H3 LOSP timber
For the samples that had been allowed to dry for 5 days, there was no effect on the surface of the polystyrene (figure 3).
Figure 3: Polystyrene in contact with 5-day old H1 PLUS timber
The presence or absence of the building wrap made no difference to the observed effects. Likewise the treated wood had no effect on the building wrap although there was some dye discolouration from the 24-hour old samples, especially the H1 PLUS. Discussion As expected, when very freshly treated LOSP treated framing is placed into intimate contact with polystyrene, some col apse of the cladding can occur. The significant difference between the H1 PLUS and H3 samples was surprising; both chemicals contain the same solvent, and under commercial conditions the fluid uptake of H3 in timber is higher than H1 PLUS (35 vs. 20 litres/m³). The active ingredients are not expected to play any part in the breakdown of polystyrene. The interpretation from this trial is that the actual uptake of fluid in the H1 PLUS samples used was unusually high, and higher
than the H3 samples. This is confirmed to an extent by the intensity of the orange dye, which appears to be significantly stronger than normal. Thus it would seem that the apparent difference has more to do with the fluid uptake of individual pieces than the type or preservative involved. The building wrap played no part in the movement of solvent which is understandable given the vapour permeable nature of the wraps and the vapour phase movement of solvent. Where a reasonable amount of drying can take place before the contact, the treated framing had no effect on the cladding. Under normal construction conditions, treated framing would have adequate time between treatment, pre-nailing, delivery and erection for the solvent levels to fall to levels that have no effect on the cladding. Where it occurred, the collapse of the polystyrene took place immediately, and then no further collapse occurred. This is consistent with the rate of loss of solvent from wood, which fol ows a typical decay-rate curve. Thus there are not expected to be any long-term, on-going effects from solvent emissions. Conclusions Placing polystyrene claddings into contact with very freshly LOSP treated framing can lead to the collapse of the surface of the cladding. The presence or absence of building wraps has no effect on this. Allowing the timber to dry for five days fol owing treatment has prevented any damage to the cladding from occurring. Under normal commercial conditions, more than five days drying would occur before cladding was fixed to framing. It is therefore expected that LOSP treated framing would be unlikely to have any adverse effects on polystyrene claddings under normal conditions of use. Terry Smith Osmose NZ
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