If you’ve determined the crack is cosmetic, you can fix it yourself in an afternoon. Here is the standard method for hairline to medium-sized cracks.
If a window frame isn't securely anchored, everyday movements like closing the window can stress the surrounding plaster. When to Worry: Diagnostic Patterns
: In regions with extreme temperature swings, different materials (like wood frames vs. masonry) expand and contract at varying rates, causing the plaster to tear.
: Water seeping through failed window seals or cracked brickwork weakens the plaster bond, causing it to crumble or "blow" away from the wall. How to Repair Wall Plaster Like a Pro - Helpful Home DIY
