to decorate my house.

there are 2 ways to do this

1 paint the whole brick your desired mortar color. then use BRICK stencil to paint the tiny brick pattern on top of that.
2 only paint the tiny mortar lines with a MORTAR stencil. then your tiny brick pattern is made of unpainted original brick.
3 if you mess up just repaint the brick & try again.

because of my 140x140mm printer build space, each stencil is 2 pcs (L&R) dovetail joined together. there are 5 different 2 pc stencils. large, medium, & small BRICK stencils. large & small MORTAR stencils. the original small stencils were sized for MY bricks (195.5mm x 56.5mm). there is also a one piece mortar stencil.

join 2 dovetail sections. tape stencil halves together.
use blue painter’s tape to tape off the surrounding area you don’t want to paint.
if using BRICK stencil, paint entire brick your desired mortar color. let it dry.
carefully align stencil & tape it in place. paint tiny bricks a nice bricky color.
if using MORTAR stencil, carefully align stencil & tape it in place.
paint tiny mortar lines on unpainted brick.

because bricks are irregular surfaces you may need to press down on the stencil in some places while you spray paint to avoid underspray leakage under the stencil edges. bamboo skewers work good for this, or your fingers (in a latex glove).
don’t spray too much at once. 2 or 3 light coats with a little drying time between to avoid drips & runs.

the 4 bricks on the corner were first done using method #1. that didn't turn out very good so i used #3 & then #2.

.3mm layers
100% infill
no support

post a make if you use this to paint your house

also check out my Flag Brick stencils https://www.thingiverse.com/thing:3979924

NOTE
if you use these on a very flat surface you may not get the best results.
these were made to paint the rough uneven bricks on my house.
some underspray under the stencil edges was unavoidable for me so i adjusted the stencils to allow for that.