splatmap textures not applying in build

in the unity editor, my splatmaps work perfectly, however when i build my terrain is just plain black.

is there a setting that i may have missed when building that is required to make the splats work ?.

editor

build

i load them in using code with

 SplatPrototype[] terrainTexture = new SplatPrototype[4]; 
         terrainTexture[0] = new SplatPrototype(); 
         terrainTexture[0].texture = (Texture2D)Resources.Load("stone");
         terrainTexture[1] = new SplatPrototype(); 
         terrainTexture[1].texture = (Texture2D)Resources.Load("sand");
         terrainTexture[2] = new SplatPrototype(); 
         terrainTexture[2].texture = (Texture2D)Resources.Load("grass");
         terrainTexture[3] = new SplatPrototype(); 
         terrainTexture[3].texture = (Texture2D)Resources.Load("snow");
 

edit i attempted adding the textures to the code as variables draged in rather than using resource.load, also didnt work

edit i ended up finding another post to a workaround which works, unfortunate that i couldnt work out a proper solution though http://answers.unity3d.com/questions/171150/terrain-basemap-texture-through-code.html