Originally Posted by mudmixer
Concrete is NOT acidic. It is an alkali material because of the materials.
Concrete is not as porous as the wood and does not absorb as much moisture.
Mechanical attachment is always best when you attach a temporary material(wood) to a more permanent material(concrete). Some sort of barrier is always good, but codes are just the minimums.
Dick -- I can cite sources that should prove my point about the acidity, particularly in new concrete that is still curing. I have them at my office, and will follow up on Monday, instead of researching this all over again.
Concrete is not as porous as wood, definitely not. But it will wick moisture that the wood does not normally have access to, and bring that to the wood substance, or really anything else, for that matter. Also, as a porous substance, it is liable to transfer moisture from elsewhere towards the wood, like any material that can sponge water would.
ETA -- Dick, I've done some quick research, and I'm clearly drastically misunderstanding whatever I was reading about this topic -- NASA agrees
with you on the pH numbers, as does the books I have on hand in my house. I'll come back Monday with a better explanation -- I KNOW I read something about the acidity level, and not the alkaline level, interfering with adhesion in new concrete. Until then, this is going to drive me nuts!