Which concrete board? I'll guess you meant to say which side faces out. It does matter with most, not the end of the world if you get it wrong with a few exceptions. So, which brand, thickness and what cha doing with it?
TILE GUY - retired- TROY, MI - Consulting by phone/internet - PAYPAL
DITRA Installs - KERDI Watertight-Mold-Free Showers. I have NEVER made a mistake, I thought I did ONCE, but, I was WRONG!A+ BBB rating - est. 1987 - over 50 yrs. exp.