Stacking spell durations?

[Smaugnolia]

A while back I was reading on some forum (It was either for pathfinder or 3.5, I forget which) and on this forum there was a build described that could get effectively hundreds of hours of mage armor a day by rules exploits. However, part of the build involved seemed to involve the assumption that if one casts mage armor (or any spell it seems) multiple times, that their durations all stack, and one does not begin to run down until the previous one is exhausted. Nobody in the forum seemed to disagree with this logic, but I can't find any mention of anything like this in rules for pathfinder or 3.5. Is this an obscure rule? A common house rule? just plain wrong?

[David knott 242]

I would go with just plain wrong. Spell durations usually begin elapsing as soon as you cast them, so they can't be "on hold" unless there is some specific effect to cause that. As a result, the durations of two Mage Armor spells on the same target would overlap and not stack.

[Bob Bob Bob]

Just wrong. Durations overlap, not stack. Casting mage armor 10 times at the start of the day just means it lasts a minute longer than usual from the first casting (because you cast the last mage armor a minute after the first). I haven't seen it as a houserule but it's entirely possible someone does that. The only benefit to multiple castings of a spell is some protection from dispelling (by requiring them to dispel more spells).