Silkspan for modeling tarpaper roofs

In the June 2004 Model Railroad, Lionel Strang constructed a simple brick garage in the "Workin' on the Railroad" column (well, finished - it was a 2 part column). He used silkspan to represent tar paper roofing, and wrote simply that he cut the silkspan into 3ft wide strips (standard tar paper roll width), and "painted" the silkspan onto the roof with Polly Scale Tarnished Black paint.
OK, since my current methods of representing tar paper roofing (which is very common for flat roofs of most small businesses in the North East) using masking tape or painted tissue paper leave much to be desired, who here has tried this and what are the results (I only bring it up, because scanning the web indicates that most Airplane modellers using silkspan first coat their surfaces with nitrate dope first - he obviously didn't).

I still like the masking tape method... except modify it: go to an art story and get BLACK gaffer's tape... it's super-tacky, and it already looks like tarpaper.

Another method I use: 400 or 600 grit sandpaper... tear the edge of it, and it looks like torn tarpaper. I would use black oil paints applied with a toothpick or needletip to simulate the tar over the lap joints.

-otto-