Direct Answer
No — you should never perform fabrication work based on verbal instructions without written confirmation. Verbal instructions are not contractually binding, cannot be traced in a dispute, and may be misremembered or denied. Ask for written confirmation (email is sufficient) before acting on any instruction that changes what you fabricate.
Full Explanation
On fast-track projects, verbal instructions are common — but they create legal risk. The engineer might verbally approve a field modification; the GC's project manager might verbally authorize a connection upgrade. These are often made in good faith, but when the project is over and costs are being scrutinized, verbal instructions become 'I don't recall saying that.' Even a quick email — 'Per your verbal direction today to add a stiffener at gridline D-5, please confirm in writing' — creates a paper trail.
What This Means for Your Shop
Establish a culture on your team of 'if it's not written, it didn't happen.' This protects you, not just legally, but operationally — verbal instructions also get misunderstood and passed down incorrectly through your own organization.
Common Mistakes
Acting on a verbal instruction from a field inspector without confirming with the GC. Field inspectors often do not have authority to authorize changes.
Recommended Process
Respond to verbal instructions with: 'I understand — I'll send a quick email to confirm so we both have a record.' If the person resists written confirmation, that is a red flag worth noting.