Ian,
I have no experience of plastic chairs on wooden sleepers outdoors - the layouts I have worked on had whitemetal chairs pinned on traditional coarse scale sleepers themselves pinned to battens, copperclad soldered, and Peco. Indoors, they’re fine, afaik. I hope.
if I were going outdoors now I would use Peco, as its long term reliability is established. All you have to do is clean it.
The pins needed re-inserting with tedious regularity, and after a time the copper dissolved, evaporated or oxidised, possibly all three, as what was left would not hold the rails to gauge, and can’t be soldered to, not matter how much flux you use. To be fair, the copperclad pointwork gave good service for twenty years, and was within a couple of hundred metres of the sea, but was recently replaced with Peco.
I’d be concerned about the UV stability of the plastic used for the chairs, the general stability of the wooden longitudinals, and the expected lifetime of the glued joint between them. I guess the loads are not high if the rails are straight and they can move lengthways in the chairs as they expand & contract relative to the timber and the steel. That suggests that maybe greasing the rail with something like silicone when building it might help. Don’t get the silicone on the models!
I guess some mechanically fixed cast brass chairs, interspersed amongst the plastic ones might be a reliable solution?
hth
Simon
