Sorry Adrene of course most of this post, refers to painting Drop cloths & not tabs or Travelers!

 The more I think about this! Why not just use a Scrim Tab/ Traveller?
This will give the extra option of being able to transpose it with lighting, as well as to Tab it Out & In!
Any see through Scrim Net material will work.
With the scrim on a tab track, run it from one side to the other side of the stage, rather than as a 2 piece tab curtain, as this will give better sight lines & uninterrupted vision, when transposing the lighting.
The wall can be painted on to the scrim. Then when the lighting is put on upstage & reduced down stage, the wall disappears. Reversing the lighting the wall will appear again!
The paint won?t crack & it will fold easier, because the fabric is net.
Use Rosco Saturated paint, which can be diluted up to 15:1 before any appreciable colour loss.
Using a heavily diluted paint, you can spray the block colour on. Either using a domestic vacuum cleaner spray gun or one of those plastic garden spray bottles, with the adjustable spray flow nozzles.
You can do this while the scrim is hung on the tab & after it is dry. Take it down & lay into on the stage to add the brick work.
As suggested by Joan keep it on the square, with the mortar lines.
Use the chalk line for the horizontal lines & an exact brick size.