I do, thus my comment.

The key is to use this to your advantage.

It depends on the environment - many years ago I used to have temp job in the summer working on a large industrial plant that had a nice office building where the managers and admin staff were based. There were no signs saying "temp staff keep out" - and you did occasionally have to go in there but it was pretty clear to me that you couldn't go and hang out in there - particularly as the temps got all the muckiest, smelliest jobs in all weathers.

In my experience, it isn't necessarily classist horseshit that divides office and shop (or field) workers.

> They’d followed my oily bootprints down the hallway and begun to leer. Who is this diesel-stinking contractor?

That's probably the real reason. Being a welder is messy, stinky work and office workers don't want that in their space.