Concrete Taxiway

Tarmac, taxiways and flightlines don't have standard grids. I would just "score" the squares on the sandpapers. I would paint different shades on some of the squares. Modern tarmac are usually clean of oil stains. However you can see tire marks. You can also add some "black rubber seal" between grids and cracks to simulate concrete repair.

To get an idea of tarmac grid sizes use Google maps and zoom in on an airport and you can roughly measure the size of the concrete squares  right off the screen using the scale on the bottom.

 I have duplicated runway using plaster, scoring with a No. 11 blade and used dark grey card for the expansion material. I used acrylic artist paints for the markings and weathered them by pulling bits off with masking tape.

I would doubt they are that small that you'd need to make a checkerboard. What I would do is make your base however and just add one seam on the base. Or even a cross. Like the bird happens to be sitting where 4 "slabs" all meet.

Shep Paine showed a way to make the black tar "beads" between these slabs. He used black artist oil paint in a syringe. Just squirt it out along the seam line like you were calking a window or such.

If you are wanting the oil stains I'd say thin some black way way way doin and drip it on in a few small spots. build up till you have the effect you want. Be sure to vary the thinned paint some cuz oilstains aren't straight black. use a little dark brown thinned way down too.

All the time I spent on the flight line at Oceana and I never could remember how big the squares where. I would say 10x15 and modern ramp/tarmac where very dirty with stains. different airfield would have different dimensions, depends one when they were made, what size aircraft it was designed to support, etc.

Our parking spaces for our Tomcats were almost black from stains. I would think the Air Force keeps their parking areas a little cleaner but there will be stains. I would recommend thinning down some black, brown and dark grey and "dripping" them onto your tarmac to simulate stains then using a dry brush, wipe it in different directions. HTH

Reddog