My only suggestion

is use blue painters tape pushed down slightly and dry brush lines so paint won’t creep under paint.

PVA Primer or Drywall Primer

Some sort of Drywall PVA Primer from Home Depot.  Paint does not stick to dusty surfaces like Drywall,  if you can wipe your hand on it and it makes your hand dusty, paint will not stick.

Rust-Oleum Corporation 01501 Drywall Primer, 1-Gallon, White - https://amzn.to/3qGLDT8

Cut your tape

Cut your tape in as narrow a strip as you can that will stick to the road surface. When you peel it off the surface any lifting of paint should be minor enough to leave as is or pretty easy to touch up with a tiny brush.

 By the way, are you using any dark coloring agent in the drywall mud? That would make the paint lifting issue look like natural wear instead of a bunch of white spots.

The other way is to use decals on blacktop.

Rick's got the

right idea regarding narrow width tape.  I press it against my tee shirt first to contaminate the adhesive with some fuzz.  This reduces the stickiness somewhat.  If you are concerned about paint running under the tape, first apply a very thin coat of the road color and let it run under, if it wants to.  When that's dry go back with the yellow.  Remove the tape immediately by pulling it back horizontally along the road.  This creates the thinnest point of separation insuring no peeling. Never ever pull straight up !  If you have trouble keeping the two pieces of tape parallel you can bolt two #11 blades together, through that small slot, with a washer in between.  Use a straight edge and score one piece of tape right down the center.

white lines?

anyone had any success doing road markings with  stencils and an airbrush? .....DaveB 

DaveB

I've tried...Lord knows I've tried! Admittedly at that stage of my current layout the roads were smoothed drywall mud but the various small changes in the surface just didn't lend itself to template use. Maybe with a more even surface like fully painted EVA foam it might be possible......it certainly was a frustrating experience at the time.

Dry Transfer

I tried some Woodland Scenics white dry transfer lines.  This was on a surface of EVA foam, ala Rick Sutton.  I was a bit apprehensive that the dry transfers wouldn't stick well, so I brush painted a coat of clear flat acrylic paint over the lines.  The dried acrylic disappeared, and the lines were sealed to the road.

Not sure how that would work over drywall mud, etc., although maybe if sealed per Az's suggestion, it might work.

Al Carter, Mount Vernon, WA

Paint Pens

As an alternative, consider using paint pens such as those made by Craft Smart. The last couple of years I have been using them on my roads. I use a straight edge as a guide for both the centre lines and the edge lines. For the curves I use a Flexi curve. They are cheap enough and easy to find in North America at craft stores such as Michaels and Hobby Lobby. Originally my roads were made of dry wall mud sprayed with Rust-oleum grey primer and weathered with artists acrylics applied with sponges. But, after seeing the great results of Kathy Millatt and Rick Sutton's roads, the last 12 months, I have been building them from EVA foam.

Frog Tape

Frog Tape has a product designed for delicate surfaces although the regular frog tape may work fine.  There is also stick on traffic lines available which is what I used for my road.

Checkout my how-to video on making roads with foam sheets.  It may give you some useful tips including the brand and installation of my traffic lines.

Joe