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Can seasonal frame movement crack the caulk at a fiberglass window?
Fiberglass is often described as dimensionally stable, but I’m curious how much seasonal temperature change can still affect the frame where it meets siding or trim. How does that movement compare with vinyl or wood, especially where the window gets strong sun?
If a caulk bead or nearby finish develops a hairline crack, which locations or changes over the seasons would help distinguish ordinary joint movement from something that deserves a closer look? I wouldn’t assume a visible gap means the frame is defective or was installed incorrectly. What joint details would you want an installer to inspect?
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- Since a hairline crack alone doesn’t establish the cause, I’d have the installer check the joint’s width and depth and whether the sealant bonds to just the two opposing faces. A bead that’s too narrow or bonded on three sides can be strained as the joint moves. If the geometry is the issue, simply applying new caulk may not hold; the joint may need to be corrected first.