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The Boston Globe


Handyman on Call

Why is his hardwood floor cupping?

Q. The hardwood flooring closest to an outside wall in a bedroom is cupping downward. It does this mostly in the winter: Center bowing up, edges down. The floor is always dry but cold in winter. PETER, in Hotton’s chat room

A. Cupping usually occurs when the wood takes on moisture and expands, which is unlikely to happen when the wood is dry. But you say the wood is cold in winter, which leads me to believe that water vapor under the boards condenses on the cool boards and enters the unfinished part (bottom) of the board, causing the cupping. Cupping also may occur when the boards get moist and expand, but have no place to expand to except up. I think the cupping will go down in summer, when the water vapor under the boards is less likely to condense.

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