I do a fair amount of concrete forms for sidewalk repairs, concrete pads, and even dabbled a bit in concrete counter tops. I try to stay away from the kerosene or diesel (don't like the flammable nature of it and what it tends to do to the surrounding area). I use plain-old mineral oil. As long as there is a good coating (slick to the touch but not dripping) it works great. I normally spray it on heavy with a spray bottle and then go back over it with a cheap paint brush to spread it around evenly and work it into the wood form and it seems to do the trick. Pros - nonflammable, doesn't kill grass, Cons - Wife hates it when I use up all the mineral oil which she uses to treat our butcher shop butcher block.