When I decided I will make Earth build for Engineer, I definitely did not expect it will end up this strong. Sadly, new Earth skills from legendary weapon didnt really fit well in here. Instead, we are using first weapon to have free Fragility source (artifact power). On top of that we have free shattered source from Engineer passive tree (Shattered on Hit). Unfortunately the build is a little RNG dependant, there are few rare passives that can boost our damage by quite a lot (for example Apptitude to Prowess passive) but even unlucky run can reah O13.  
  
Skills:  
Rolling Boulder  - Our main damage dealer. The more AoE we have (our character, not the skill) the higher damage multiplier on it. First Earth Skill  
Earth Bolt - Source of Collosal which gives us a lot of extra AoE (meaning higher DMG multiplier for Boulder). Also great to trigger other support skills with Skill Chains. Second Earth Skill for Skill Chains and Group Passives  
Ammo Box - Constantly provides us with Ammunition, which gives us huge damage boost. First Blast skill  
Weakening Shot - Source of Exposed to increase our Damage further. Second Blast skill for Group Passives (no Skill Chains, Ammo Box has too high CD)  
Explosive Trap - Source of Disoriented to incrase our Crit Damage  
Burst of Lead - Source of Dazed to incrase our Crit Chance. Also generates Apptitude to increase our Crit Damage (with few Earth to Projectile Chains we are able to reach soft cap of 800 Apptitude)  
  
Skill Passives: Our main damage dealer of this build is Rolling Boulder, so passives to it take priority(AoE passives for it do not increase its damage so take them only when there is nothing better available). Attack Speed to Earth Bolt is also important, try to reach 0.2s CD on it to generate as much Collosal as possible. +Quantity to Ammo Box is also very important, take it every time. For the rest of the skills focus on Cast Frequency/Multicast, ignore DMG and AoE for them.  
  
Stats passives:  
Offense: Priority above everything else is AoE, to increase Damage Multiplier on Boulder.  
After that priority is Cast Frequency, Multicast, Crit Chance, Crit Damage and Damage  
Defense - Prioritize HP untill you reach 500 to unlock full boost from rune. After that take Armor/Block/HP whenever there is nothing better available  
  
Other passives:  
Grab all Skill Chains whenever they appear (Earth to Projectile being most important)  
Take Slow and Disarray on Cirt once, ignore them after  
For Ascension we only take white tier passive  
  
Synergies:  
Take Slow to Disarray synergy once, ignore it after. Ignore Disarray to Bleed synergy. Take Apptitude to Prowess synergy if you find it, its huge boost to our damage.  
  
Banish list:  
Prioritze EXP early on, banish it once you reach 200% extra  
Banish Leviathan  
Banish Slow on Hit after you take both white and green tier (they count separately for the synergy)  
Banish Disarray on Hit after taking green tier once (its enough to reach soft cap)  
Banish Bleed on Hit  
Banish Crit to Non Earth Skills  
Banish Damage to Non Earth Skills  
Banish Damage to Frontal Skills  
Banish Damage to Lasting Skills  
Banish Damage to Physical Skills (this one is quite rare, you can banish AoE to Lasting Skills instead)  
  
List of Curses:  
So why 40 Curse Intensity instead 64? Because going past that gives no extra reward, just extra challenge. So to maximize reward, pick Scorching Valley map and those curses:  
Level I: Lifeless Void, Reckless Goblins, Captains of the Void, Revenge of the Void  
Level II: Reckless Goblins, Clone Army, Unholy Reinforcements  
Level III: Clone Army, Unholy Reinforcements, House of Lords, Council of Lords  
Level IV: Clone Army, House of Lords, Council of Lords  
Level V: Clone Army, Unholy Reinforcements, House of Lords, Council of Lords  
Level VI: Lifeless Void, Unholy Reinforcement, Revenge of the Void, Void Presence  
Level VII: Clone Army, Unholy Reinforcements, Ethereal Lords  
  
Runes:  
Minor - Pick two of the following, depending what you want to farm (Material Harvest - materials, Efficient Extraction - Void Essences (boss parts), Ardous Training - Prestige). For 3rd rune pick Endless Refill  
Major - Fateful Strike, Vulnerable Exploit, Savage Strike, Frozen Blood  
  
Only mandatory rune in here is Frozen Blood to give us Slow passives (which lead to Disarray). Other runes are just whatever biggest damage multiplier is available.  
Since Apptitude to Prowess synergy can be huge damage boost (and as shown in the video, you can be unlucky and not find it even once) you can replace Vulnerable Exploit with Synergetic. If you do that, you also need to change your banish list a little (because you will have increased chance to find useless passives)  
Banish Slow to Disarray after taking it once (replaces EXP banish)  
Banish Disarray on Hit w/o taking it at all, dont take Disarray on Crit either (to not unlock Disarray to Bleed synergy)  
Banish Apptitude to Prowess synergy after you reach 800 Prowess soft cap (replace Damage to Physical banish)

Material Farmer - Engineer Void Fields Guide