Is it possible to add custom textures to map editor?

I created a 256x256 TGA texture and placed it in "Steam\steamapps\common\DoorKickers\data\textures\editor\brushes\concrete\my_texture.tga". But it won't show up in the map editor.

Also the size of my texture is only about 3kB while official textures of similar image size take more space (up to 190kB). Did I forget to add something? I used GIMP for creating the texture file.