Inside Interior Doors - This Old House

Shopping for a paint-ready interior door can be confusing, since you can’t see what’s underneath the primer. If a traditional wood door (generally pine or poplar) is what you’re after, you’ll have to special-order it—and expect it to expand and contract with changes in humidity. Here’s how other interior doors are built today.

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Inside Interior Doors - This Old House

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Earth's inner core - Wikipedia

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