Get 1/2"X 15" X ??" styrofoam (length is your choice). Lay masking tape to sim centerlines which are white. Scale centerlines ought to be scales to 18", taxiways 12". For taxiway or ramp markings spray some yellow on the centerline then lay masking tape over it. Apply spray cans of black for new blacktop or gray for concrete. You can even mask out runway numbers, hold short lines, parking T’s.
A 100’ wide runway is is about 24" in 1/48. 15" in 1/72.
For my photo backdrops, I always include some of the ramp or taxiways in bottom of shot.
Then, I select the taxiway portion, copy, and paste to a new image. Now, the resulting strip will be far too narrow to represent a taxiway. I resize the photo, first unchecking the box that holds the aspect ratio the same as original. I then greatly increase the height of the image while leaving the width the same as original. I do this resizing by trial and error until I get the taxiway or ramp the dimensions I want. The color of the tarmac is retained, as are tar seams and cracks.
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It’s just a sheet of sand paper, with various shades of grey sprayed at it. There are various shades of grey sand papers already, so there’s a good start point.
I used a straight edge and penciled in the lines, then a fine brush with black paint for the rubber crack filler in the expansion joints.
I used contact cement to glue it down. That works fine for a smaller sized base, but not so good for big stuff. I’d recommend a better adhesive.
This one is for 1/32. You can clearly see that the sand paper is peeling up along the edges, there’s also some “bubbling”. I will not be using contact cement for this sort of thing, ever again!
The oil drips/stains are thinner with just a dab of black paint mixed in. I did the brush, then flick the handle, splattering the drips. Bigger spills/drips/stains are done by just touching the brush to the area.