Absolutely!! yes it is VERY common with most if not all of our structural and misc steel projects.
Your lucky it's only 10% retainage, it's not uncommon that they'll only pay 75%, then that last 25% they owe you, they'll cut in in half and half again so it takes 2 yrs to get the last 5% that usually is only about $5000 on what started out as a 1 million project.
Also yes you have to nag them it's just how its done, don't think they;ll just send a check cause its made the date it was supposed to, call them and remind, threaten whatever it takes to get the money, it's just business, at least in the Northeast that's how it is.