High Moisture Content Creates Cupped Oak Floor


I have a 2.25 oak floor that was laid about 40 years ago. It has a urethane clear finish about 5yrs.old. A 2×5 ft. section is cupping at this time in middle of room. Can you tell me what can be done to correct it?


Dear Al

That’s a strange place for boards to be cupping. It usually occurs on the side of the floor where water has seeped into the edge, from outside. If the warping is anywhere near the edge check the side if the building for water incursion (rain gutter overflows etc.), even if it happened a month ago. Grill (in a nice way) your household members to see if anyone has spilled water in that area. Or maybe while you were away some pipe has leaked and wetted the floor, or a hanging plant was watered and overflowed.

You see, the point is that the wood warped because of excess moisture exposure. So it is more important that you find the source of the moisture, so this doesn’t keep occurring. It may simply be a damp summer time basement. In that case you will need to install a dehumidifier in the basement all summer long.

But what you do now is nothing. Except of course check for all those moisture sources. The current winter heating season will dry out the floor, and it you are lucky the boards will flatten somewhat on their own.

If you want to buy some tools to be more precise about the whole issue, you can buy a moisture meter at http://www.leevalley.com. Order prod.#99N15.01. You shouldn’t do any repairs or sanding of the affected boards until they reach a moisture content of 6-9%. This last figure depends on the average MC of indoor wood in your region, check with local floormen, or wood workers.

Next, check the relative indoor humidity with a wet-dry bulb hygrometer at http://www.e-sci.com. Order prod. # 848N635. You should be keeping your relative indoor humidity within 40-60% all year round. Don’t let the floor experience extreme 30% or more humidity changes or cupping will result. It can take about a month for these effects to show up in the wood, and old floors with exposed seams are really subject to humidity changes.

Only after checking all these factors would I consider having that area sanded flat again, and touching up the finish. Consider having a professional do this. If you don’t address the moisture problem, and sand the boards flat now, they could very well warp again, leaving you with less floor to sand each time.