Build I am using for Dungeons and Veterans (Minus what I am missing because of Elder Gems)
Breakdown:
Base - Must have for any Eng Tank, any time you are above 70 volatility hit this.
T8 - Another must have, you will be spamming this, a lot, basic threat builder.
T4 - Primary volatility builder due to lack of flack cannon, try and use on every CD
Useful to replenish shields for yourself and group. T4 as soon as you have extra ability points
Excellent addition to your shield mitigation.
T4 - Also a must have here as a volatility builder, usually use on every CD
I run zap in 5 mans because as the tank I am almost always in range to stun.
Base - Love having a second taunt since hyperwave is in the rotation its usually on CD when you need it most, also useful to help prevent AoE damage and build threat.