Locking Brakes when wet

Basically the title says it all, I have a 95 s-10 blazer and when the rear brakes get wet they lock up, They release when you let off the peddle but cause braking to be very hard. Mainly does it if for example your out driving in the rain and you let the car sit for an hour or more. Any suggestions?

just on inital break after the sit or does it linger after the first stop or 2?

It does it in the first stop or so, till it's warm is what i would consider the timing to be when it stops.

ide say it is normal, mine does it, and ive seen several posts on it, its a fine layer of rust that builds up, if it does it more and more then you have a problem,b ut once or twice is fine

If in doubt just pull the drums and inspect them.
This'll also remove the dust, which might help

Take them apart an blast them with brake cleaner. Chances are you have a build up of brake dust gumming up the works and holding onto the moisture. Once they get hot the moisture dissapates and work fine.