Hello Zero3,
This effect may be due to the fact that 2 solids intersect.
Take for instance where two thick walls meet at a corner.
Each wall is in effect a tall rectangle meeting at right angles.
At the corner you will get this ragged or bleeding effect for the extent of the width of the walls.
This is where, mathematically, you have two faces occupying the same space.
From what I understand it may be better to have these two walls as two separate entities for rendering purposes.
However, to get round this bleedin' problem what you do is chamfer the meeting corners of each wall at 45 degrees, like a picture frame.
What happens with other shapes..I dunno.
What sort of shapes are you working with....dare I ask!!
Does this help?
Best of luck.
regards
Stephen