Re: Sand paper clogging with thick brown substance
it looks like shellac to me, that was a common product years ago for sealing floors. shellac is wax based and thats where the problem lies it gums up the drums on the sander.
im surprised the rental shop didnt tell you to wash down the floors a few times with T.S.P. it will help break down the dirt and grim along with some of the wax so that the sanding drums will last longer.
just as an example, well i sanded my floors 2 years ago, washed em down with tsp 3 times. once finished i spent about $310 for the rental, sanding drums, discs and polyeurathane. a buddy did his place the same month and went straight to sanding, he spent over $1000 in supplies and rental. mind you i get rental gear much cheaper do to pro rate but that only would have made a difference of $100. he just kept burning through drums like crazy
fire up the saw and make some dust