There are two types of treated pine, have a look at this site for a quick explanation http://gtpine.com.au/other_information/cca_or_acq
Having a good supply here we’ve used heaps of both around the families properties. Mostly ACQ for anything that’s for the kids or sat on and CCA for pergolas, retaining walls etc. ACQ is more expensive for sure.
There is a bitumen based paint to put on any parts the are in ground, can’t be bothered going out in the cold to check the name
Our pergolas have been up about 18 years and no issues at all, same with the retaining wall. We did replace the balcony with structural treated pine as the oregon turned to crap within about seven years.
If you’re going to paint it then do it before you put it in place.
Edit:
Just saw Cuppa’s post. In Australia about thirty years ago we imported lots of Oregon from the forests damaged by the Mount Saint Helens volcano eruption in Washington. This was found to have issues and rotted quite quickly. Plenty of pergolas were built with it as it was cheap for a reason.
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