i had the same problems in our old house and was told by an old timer to get a masonery? brick and start scrubbing. this is a pumice like brick on an easy to hold handle. i had to special order one from the hardware store, but it worked like a charm! i have wallpapered 3 rooms since (removal of old paper and smoothing very bumpy old plastered walls) and the brick still looks like new. well worth the $$$. good luck!