The “mix" is a wood treatment made of 75% Mineral Spirits , and 25% Polyurethane varnish (cheaper the better) , It’s applied prior to priming and painting and helps seal all the pores in the wood to prevent water intrusion = ROT !!!
You can even apply it at this building stage because it won’t interact with foam or TB2 . The ideal is to slobber on several coats till the wood won’t take anymore (gets shiny) , let that then dry and prime/paint and it’ll be good for a long time ...
Untreated wood is susceptible to the first leak that comes along , or even our infamous humidity ...
If I forget to treat wood here , I end up regretting it ...
Funny , this is how this all got started ... with “the mix” .