Ok, I know that this is going to sound stupid and many of you are going to think that I'm trolling. I promise that I'm not...
I need to make four wooden forms to produce concrete (actually quick setting mortar) building blocks to make garden beds. Two forms will be six feet long by eight inches wide by two inches high and the other two will be the same but three feet long each. A long form or two of the short ones will take exactly one bag of quick setting mortar. Each of the forms will be put together with stainless steel bolts, washers and inserts. You can see what I'm talking about in this YouTube video:
https://www.youtube.com/watch?v=x7jz96MDvyo
But I'm going to be making a bunch of these - perhaps fifteen or twenty sets. I want to use 6/4 poplar for the bottom and 3/4 poplar for the sides. The wooden parts need to protected from the mortar - which is vicious stuff if you've never mixed it yourself. The forms need to last until I finish them all. This will take two or three weeks at one set per day. What do you suggest for a finish? It's not for looks - even some kind of paint is acceptable.