What the customer can actually see
They cannot judge a joint, a weld or a membrane detail. They can judge whether the crew arrived on time, whether the site was left tidy, and whether anyone told them the job would run a day late.
Those observable things become their assessment of the whole job, including the parts they cannot see.
Silence is never neutral
A customer who has not heard from you assumes the worst available explanation. That assumption hardens over a few days and is difficult to correct afterwards.
A short update with nothing to report still resets the clock.
Delivering bad news
Delays and unexpected findings are normal. What determines the reaction is timing: the same delay reported on the day it becomes known is a professional update, and reported on the deadline it is a failure.
Early disclosure also gives the customer options, which is what they usually want most.