I am using Treebark for rock castings. How long and at what temperature should I heat them in the oven to kill microorganisms?
thanks, Rob
That depends. If you are going to use rubbery material to make a mold from the tree bark to make future castings then you wouldn't really be introducing the tree bark into the home long enough to need to kill the wee beasties living in it. You'd be throwing the bark away once the mold is made.
If you intend to use the tree bark to actually be the model of a rock face as suggested in the August 2014 MR article, then rather than follow that author's advice about putting the bark in the freezer (below zero cold does not kill the organisms as those of us who live in the north can see each spring) but instead follow the advice in Nathan Kimmel's corrective letter published in the October issue: baking for 2 to 4 hours at 250. He wrote that thinner pieces need less time; thicker pieces might need more. I would only add that baking tree bark won't smell like tasty food so warn the other inhabitants of the house -- especially She Who Must Be Obeyed -- what you are doing.
Dave Nelson
I always bake soil before using it on the layout. I just put it in foil pans and put it on the grill for an hour or two, works great and no grief from the smell. I would do the same for your bark.