Mobilization is the front end of every construction project: setting up the field office trailer, installing temporary fencing and signage, bringing in dumpsters and portable toilets, connecting temporary utilities, marshaling key equipment, and getting first crews on site. It happens after notice to proceed and before any productive work. Mobilization costs are real and often substantial: trailer delivery and setup, fencing materials and labor, utility connections, signage, and several days of supervisor and labor time.
Most commercial contracts allow mobilization as a separate pay-application line item, often capped at 5 to 10% of contract value. Owners sometimes resist (fearing the contractor will mobilize, get paid, then walk), so the cap and the verification (photos, delivery tickets, COI updates) matter. Underbidding mobilization is a common small-shop estimating mistake; the cost is invisible until you actually have to build temporary roads, run a 200-foot temporary water line, and stand up a fenced compound.