Wouldn’t recommend unless you’re desperate. - If it’s just a tiny crack, I’d patch for now—but if you see mold or feel cold air, replacement’s probably the way to go.
That “looked solid for a year... then winter hit, and boom, back to square one” line—yeah, that’s exactly what I see over and over. Patching fiberglass frames always *seems* like a good idea at first, especially if you’re watching the budget. But honestly, how many patches actually last more than a season or two? There’s just too much movement with temperature swings.
I get wanting to avoid the cost, but if you’re already noticing “musty smell creeping in,” or any draftiness, it’s probably not just about looks anymore. Mold behind the frame is a pain to deal with and can get expensive fast… sometimes more than just biting the bullet on new windows.
Duct tape—I’ve seen people try it too. Never ends well. If it’s a hairline crack and you’re in a mild climate, maybe patching buys you time. But if you live anywhere that gets real winters? Replacement’s usually worth the upfront pain.
Not saying patching never works, but I wouldn’t bet on it long-term. Peace of mind counts for something.