Cupping in middle of room after hardwood installation

Q: I had an old 50+ year wood floor that was upstairs in my house that I took out and reinstalled during a remodel. The floor went down well and looked fine for about 2 weeks. I had someone come and sand, stain, and seal. Sanding was fine, but after staining and poly, something like 5 rows appears to be cupping, only 1 day after poly (rest of the floor is not cupping).

No water issues and not installed over crawl space or anything. Could this be because of the stain and poly in the specific area?

A: Well, wood cups away from the ‘wet’ side toward the dry side. You have raised edges or cupping indicating the underside has a moisture imbalance. If excess water was applied to the top surface the boards would curl the other way, downward on the edges called crowning. This is very isolated to a small area. Is it possible someone spilled something on the underfloor in that area? Or if you had the old flooring stacked before reinstallation, one bunch of boards had something spilled on them? Is this in front of a window or radiator with a possible leak and water seeping under the floor? Has anyone put a moisture meter on the floor to take a reading?

Follow-up Q: Not near a window and no radiator. No water issues that I know of. Only thing I know the person staining it used water popping and maybe it seeped under the floor before it was stained and sealed. Also sealing took place quickly. Like two coats in one day.

A: Water popping only wets the surface of the floor to open the wood grain. It is not flooding the floor. If they applied two coats in a day it is probably water based finish. I would not expect that to cause an issue at all. In fact, this issue is confined to a small section, not the whole floor. If it was any of what you describe, why is the problem not everywhere?

Follow-up Q: I am wondering if they spilled water on it while doing the water popping, since it is just in one area where it is cupping. It is very strange. The rest of the floor looks fine. I know it had to have happened after they did the finish, because 1) it looked fine before they came 2) the floor is more than acclimatized to the area (it has been in the house well over 5 decades) 3) no professional would have sanded a floor that was cupped 4) the floor is cupped and not crowned, meaning even if they had sanded a cupped floor, when it when back to normal it would be crowned 5) it is isolated to a small area and I know for a fact because the whole floor was remodeled, that there is no water line under the floor, and not on an exterior wall where it is happening.

The only thing that makes sense to me is since it is a fairly central area where the problem is happening is that it may be where they set up a bucket or something when doing the water popping and spilled water on the floor which then was subsequently sealed, thus preventing the wood from drying out, and now it is cupped.

Does this sound reasonable?

A: I can only make guesses at this. You are correct in your assessments. The floor is more than acclimated to the house. If there was a moisture issue before sanding, causing the wood to cup and then it was sanded before the wood stabilized, you are correct. It would have then crowned. It is just in one area. 2 coats in a day, I have to assume it was a water based coating used. The recommended procedure is to take a number of reading of the floor with a moisture meter and work out an average. After applying the finish and it is dry to walk on those readings are to be repeated until the floor has returned to the average moisture reading they first recorded. Then it is ready to coat again. I think there is a possibility they may have spilled the finish or left a puddle sit too long and that area just got too wet. If the previous coat had not yet returned to the initial moisture reading of the floor it is also possible all the water had not yet evaporated from the first coat and got locked into the coating.

Follow-up: So I have an update for you. Cut out some sections of the floor yesterday and followed the water. Boards, plywood, and paper were all soaked and still wet about a week after sanded and sealed.

Even though no one has still not owned up to the mistake, it is blatantly obvious that someone spilled a large amount of water in this section of the floor. After a back and forth with the contractor and them trying to tell me how it was my roof leaking from an ice dam, etc, etc., it turns out the water is isolated to just a small area in the middle of the floor and it is not anything wrong with my roof (thankfully) or anything else. They are replacing the sections of floor impacted by this mistake and hopefully we can move on quickly after this.

Wood Flooring Guy – Thanks for your comments! It was nice to bounce ideas around with you and appreciate your speedy replies.

A: Thanks for the update. If someone had put a moisture meter on that area it would have been off the chart. It would have taken a very long time for that water to dry without removing the boards. Pretty hard to explain how it could be a roof leak when it is in the middle of the room. No evidence of water leaking through the ceiling or down the walls. No paint blistering or peeling off etc. I hope they let the sub floor completely dry before they proceed or the new boards will cup again. The plywood should not have moisture readings more than 4% above the reading on your hardwood.

Leave a Comment