Why does revit have this kind of artefacts?

[luka_kurdgelia]

[iainsavage]

More information required from you but to me this looks like a graphics display issue causing pixelation.

Might be a problem with your hardware.

[HVAC-Novice]

Create a PDF and see if that problem persists on PDF. if it doesn't, it won't matter. 

What hardware do you have and are drivers up to date? Hardware acceleration enabled? This looks like a GPU problem. 

[RSomppi]

Please indicate what you consider "artefacts".