Concentration Damage% Bonus

Does the Concentration's (water powder's armor special) +damage% bonus add with each other?, like if I cast meteor (2 mana with 129 intelligence points) twice am I going to do 120% of my damage (100%[my standard damage]+5%[1 mana]+5%[1 mana]+5%[1 mana]+5%[1 mana])?

Also, what's the limit to the damage% bonus?

 

The Concentration powder special should stack, but it doesn't, as it's bugged right now.