Ok. You mention about mesh edges. The gray pattern in your image is result of z-fighting, like you expected. Do you mean that it's resulting from the mes edges?
I would like you to check if there are two objects or two faces of the same object (which should not be possible in real world object) are on the same place. You can check this easily by first selecting the object from the place of z-fighting, then press backspace, that hides the selected object.
If you now see another object there, then that's the reason for z-fighting.
If there is only one object, is it possible for you to get such part of that model exported separately, that you could send that to me?
What software is used to create that ifc file?
Best regards,
Marko Myllymaa