So when rendered it looks good. Now all bricks are exact same size. 100 objects? Piece of cake.

But from side view, texture looks stretched.

That’s because we were using planar projection (default one). Change it to TriPlanar (box)

Now it looks better.

Now, I’m going to show you how to create decal on one of the walls. First create layeredTexture.

Grab projection1 using MMB to color attribute of the layeredTexture. Also you can set blend mode to none. It doesn’t matter since this layer is the bottom layer.

Create another file texture, as projection. Find some grayscale decal texture.

Move placement to the second wall.

Then in layeredTexture node click left to blue rectangle. This will create another layer. Remember right is down here. Set blend mode to multiply (like in Photoshop) and MMB drag projection2 to the color of that layer. So now wall texture is multiplied by decal texture. This is simple case. If you want you could use texture with alpha mask to define how layer looks. Then just grab mask to swatch right to alpha attribute. Then you would use over (it like normal in Photoshop).