Bowed flooring in front of refrigerator

Q: We have lived in our home for one year. When we moved in we had our red oak hardwood floors refinished. We also had our crawlspace treated so that it is clean and dry. Now, over the past 3 months of summer, an irregularly shaped area of flooring has become bowed, starting with a couple of feet and spreading to become about 20 sq ft. The area is in front of the refrigerator and extends into our pantry, which is beside the refrigerator, separated by a small drywall. We have had the appliance repairman out (fridge works fine), the crawl space guy out (no evidence of moisture anywhere), the plumber (no evidence of leak), the foundation expert (nothing). All meter readings say floors read at 8% and crawl space humidity is very low and dry. Floor guy ripped up boards in pantry. We found evidence of staining on subfloor! However the color of the floorboards is yellow, not black or dark as would be expected from water. We are assuming (?) there has been some previous spill, oil-related (?) that seeped into subfloor. Either way we are having floors replaced in the area, but I’m asking: do you agree with this assessment, and is there anything we should do to prep the subfloor before laying new floor over it? It appears dry now.

A: Cupping is caused by excessive moisture imbalance on the underside of the floor. As soon as I saw the sentence ‘in front of the refrigerator’ I thought ‘oh no. his ice maker is leaking’. Or the pan under the appliance that catches defrost water has over flowed.

The only advice I can offer at this point is that ‘appear dry’ isn’t enough. The sub floor and new floor need to be checked with a moisture meter and not be more than 4% difference between the 2, with 7-9% generally considered normal for hardwood such as oak. Have the new flooring in the room for a week before installing.

Will floor cupping go away on it’s own?

Q: We have cupping from a recent leak. We had our red oak floors refinished a few months ago. Unfortunately, we recently had a water heater leak on to our floors and several boards now have cupping. The floors had water on them for an hour or two and we dried them with towels and fans. Below the floor is a conditioned crawl (temp is about 64 degrees and humidity around 55%). It has only been about a week since this happened. Will hardwood floor cupping go away on it’s own? Is there anything we can do to help the process along?

A: It is possible the cupping will go away on it’s own. You just need to give it time and wait to see how it reacts. I have seen floors flatten out totally.

I’m facing a similar situation. Water was dripping into the basement from the tub which is next to a bedroom with oak strip I have just completed staining and finishing. Now I will have to wait and see it anything happens to my own floor. Fans, dehumidifiers are about the best way to reduce the moisture.

Related Q: I just installed 3/4 x 5 oak. I acclimated it for 2 weeks. It is cupping slightly. Will this lay back down on it’s own in time?

A: It might lie down but you have to find out why it is cupping. Clearly there is a moisture source and because it is cupping, not crowning that source is likely from beneath. I don’t mean to say you don’t have a leak in your roof, but the moisture, if that is the case is running down the walls and under the floor. Is your floor over a crawl space?

Similar Q: Our small capacity hw heater broke and spilled water, which found it’s way down under a plywood laminate floor in our small hall. It had just been glued to old concrete. Can I remove the wood base around hall to dry it at that point and cut openings in the floor to be later infilled?

A: Given that the floor is glued down, hopefully a water proof polyurethane adhesive was used. Given that it is glued, there really isn’t any room under the floor to allow for much water to sit. I would have a dehumidifier running and wait and see if any movement starts happening in the floor. No sense getting radical if you don’t have to. You could remove the base but I wouldn’t start boring holes in the new floor just yet.

Isn’t this some version of Murphy’s law at work? You just install the floor and this happens?

Follow-up: Thank you very much. I believe you are right. Floor remains very level. I just removed a wood baseboard at the point where the water entered and wood was already dry to touch at that spot. I’ll wait and see..

Can cupping be caused by too small an expansion gap?

Q: I have a wood floor that has been cupping since installation. The installer argues that we have moisture issues and we do show high moisture ratings. However, when we take up the baseboards the wood floors have been installed up to or within 1/8 inch of the drywall. I know wood needs space to expand but I am unsure as to what size expansion gap for hardwood flooring is appropriate. Most significantly, can wood expand in width and in length? If it can expand in both directions then would it expand uniformal across rooms? (This is a first floor install over a crawl space.)

A: Wood expands across it’s width, the wider the board, the greater the expansion can be. There are formulas for calculating this, but I don’t have a chart I’m afraid. If this is 2 1/4 wide in a small room, only a 1/2′ gap may be required. Larger room, wider boards, 3/4″. You really need to correct the moisture issue though. Boards cut tight to the side walls will be part of the cause of a floor buckling. Cupping is all about too much moisture.

Cupping caused by off/on air conditioner?

Q: We installed a hardwood floor with professional installers (sanded and finished) over a large span of time, the first of May. The wood was in the house for five weeks before being installed. The customer called the second week of August to say the floor was cupping. Upon inspection the centre of the area is cupping but perimeter is not. The top surface had a reading of 12%, while the underside read 8%. I surmise they used water to clean floor, but customer denies they used water. Is there any other explanation?

A: This is not an easy job, is it? Maybe when floor guys get their heads together a problem can be figured out. Floormasters is another good source. I think, given the amount of time the wood was in the house and the amount of time before the floor cupped (3 months) really means this problem is something you caused. I have seen jobs near large bodies of water for example, where the floor was not acclimated. It was taken in, installed, sanded and finished. Within a few weeks it cupped. This job is 3 months. I am not so sure cupping indicates excessive water use in cleaning. You would more likely find crowning, where the surface is wet and the underside of the board is more dry, so it crowns with the centre of the board raising, and the edges lower. Is it possible there is a leak from above, running down a wall and under the floor? Yes, I know the underside is normal reading, but how long have they waited to call you since the cupping started? There can be only one explanation for cupping and crowning:excessive moisture. Finding the source is the tough part. Did the installers check the sub floor and the hardwood before installing to make sure it was within limits? That is 4%? If the sub floor in the centre of the room had gotten wet for some reason and they put the floor down on top of that, the result would be what you see. There has to be a reason why the middle is cupping and the edges aren’t. Still, if the sub floor was wet it would not have taken 3 months for the cupping to happen. Just thinking out loud.

Follow-up Q: If the customer turned off the air conditioning during the day and turned it on when they returned, would that cause cupping wood floors? The outer perimeter, a water closet and small hall, have no cupping. Could it be caused by not running the air conditioner and the moisture builds up and falls to floor when air conditioner is then turned on? I also read that a new home contains about 500 gallons of water from all the new materials to construct the home.

The wood sat in the home for at least 4 weeks prior to installation, the last two weeks with heat on since it was cold.

A: I think it could easily be cupped because of high humidity in the home. If it was installed at say 40% relative humidity, and that is what it was acclimated to and then the count goes up to say 84% that would be more than double the amount of airborne moisture and the floor certainly absorbs and releases this. It would be interesting to leave a hygrometer on the floor in the cupped area and see what the readings are, especially during the day when the air is turned off. I would put this down to an environmental issue.

Oak wood floor is lifting

Q: I have recently laid a oak floor in my living room and dining room. The floor has started to lift. Is hardwood floor lifting up common and does it settle down after a while?

A: No, this is not common. Did you do moisture readings of the floor and sub floor first to make sure it was safe to install the floor? Did you acclimate the floor to your home by bringing it in for 5 days or more prior to installing? Did you leave an expansion gap along end walls?

Cupping from humidity

Q: We put in a hard wood floor this February, 2008. Our room is 24 x 27. It has been really humid this past week and we have two places that are cupping. How can we fix this without tearing out the floor and starting over? We do not have air in our house.

A: Buy a dehumidifier with a digital read out. One of these units that will handle about 3000 sq. ft. and you can set it to the RH you want the house to remain at. $300 Or so, it’s good insurance for your investment.

Seams rising, creating a wavy effect

Q: I had hardwood floors installed last spring. We noticed within a few weeks that the seams were rising, creating a wavy effect. Our flooring contractor advise us that this fall when we begin to use the heat it will correct itself. It has not. What do you think?

A: Wavy hardwood floors? It sounds like your boards are cupping, leaving raised edges. This only happens in abnormally high moisture situations. The installer should have checked that the sub floor was within 4% moisture content of the flooring, and ideally the floor itself should have had a reading of 7-9%. It is particularly important also to leave an expansion gap along the side walls in case the floor expands from too high humidity or an actual water leak which would cause the floor to swell and press against the walls. I think your contractor should first come and put a moisture meter on the floor to see how it reads now. If it is within normal range but hasn’t flattened out it may need to be sanded flat. However, sanding such a floor while it still has high readings will likely cause the floor to crown, and then the middle will bow and be higher than the edges.

After having the dehumidifier running non-stop in the crawl space

Q: You were kind enough to give your opinion on our floors last fall. Now we’ve given it several months, with a dehumidifier running non-stop in the crawl space. The floors have gone down some, but there is still a noticeable cup. Apparently the wood floor installer said that it is relatively dry beneath. Although we’ve had a weird winter, it has been very dry due to heat for at least 2 months.

We’re thinking have them come back in now and resand. We tend to have very rainy wet springs/early summers (although it could also be a drought!) Does this sound reasonable to you?

A: Put all the meters on the floor and check for moisture. If it is ready to go, then give it a go. I wish I could say something more.

Severe cupping

Q: We are building a new home. It is pier and beam construction. Our cherry floors were installed in Nov. and then covered with cardboard to protect them until finishing them, last month. Uncovering revealed severe cupping and the wood was above 10% moisture and could not be finished. The flooring company suggested running heaters, which was done for 2 weeks with little result. When the contractor got the central heat running the floors began to dry out but then actually increased in moisture again. There is no water in the house or under the house. We had a lot of rain and cold in Dec. and Jan. and they are telling us this is a normal thing and the floors will be fine once dry and finished. What do you think?

A: When the floors were first installed, did anyone check the sub floor first to make sure it was within 4% of the cherry floor? If the plywood was wet, installing a floor over top would cup the floor and delay considerably the length of time it takes for the moisture to transfer through the cherry. Have you checked the RH in the home? A hygrometer and moisture meter are important tools at this point. If you have no moisture issues under the house, and no leaks from the roof or windows (this would probably cause a more localized issue) then I have to wonder about the sub floor itself.

Cupping and dehumidifier not changing things

Q: Our solid oak floors (installed in March 2006) are cupping. We were told to run a dehumidifier which we are doing, but we can’t see or feel any difference.

A: I would purchase a hygrometer from a local electronics store which can tell you what the relative humidity is in the room, or even at floor level. Moisture is the only cause of your problem. Identifying the source can be more difficult. A crawl space under the floor? A leak in the roof or a water pipe? Excess humidity? Wet mopping a floor during cleaning?

Likelihood of cupping?

Q: If we install 3/4″ x 8″ t&g solid wood, wormy red oak (finished in place) floors in the non-conventional, non-recommended fashion of fully adhering the boards over a structural concrete slab, using Sika’s T55 adhesive… and if we have no moisture drive problems from the slab and also have a well functioning humidity control system in place in the home, how likely is it that we will still experience cupping of the wood floors?

A: Cupping occurs when wood absorbs moisture faster than it can release it. The subsequent side pressure against the other boards or structure assists in pressing on the board edges and cupping results. You must be very confident in the concrete slab, your humidity control and the milling of the boards to even think of doing this. Unless the boards are all arrow straight, how are you going to pull them tight and keep them that way during the installation? This might work, but I wouldn’t bet the farm on it. I think I would install appropriate sub flooring and nail it down, and mix another width in the mix. I would also glue the end joints of the wider boards.

Cupping in kitchen and foyer

Q: We bought a home that is 12 yr. old this past February. The dining room, living room, and family room already had red oak hardwood flooring (solid). The kitchen and foyer had tile. Before we moved in we had the tile taken out and hardwood installed to match existing (hardwood sat in the house for awhile before installation). We also put it in the upstairs hallway. The newly installed hardwood is now cupping while the existing is flat. This makes me think it is not a humidity issue or else it would all be cupping – right? I live in VA which is pretty humid and would appreciate any insight you could give.

A: you mentioned that the new floor was in the house for some time before installation. So, the new wood was acclimated to the house. That is one thing we can remove from the equation. What is under the area where the new floor was installed? A crawl space perhaps?

The 2 areas for the new installation would happen to be 2 areas in the house that might be subject to the most moisture: a kitchen with lots of cooking and steam and spills, and a foyer, with wet feet. So, yes, I could see that those areas might do something funky while the older floors in the living room and dining room might not.

Wavy appearance / waves on hardwood floor

Q: My hickory 4-inch-board floors were installed in December 2005 in a brand new home. The boards are not laying completely flat. They have a wavy-like appearance and you can feel the waves with your hands. I noticed the waves on hardwood floor probably a month or so after installation. I have been waiting, thinking they might flatten out in time. Also, I hear loud “cracking sounds” coming from the flooring from time to time. Could you tell me what caused this and if there is anything that can be done about it?

A: It sounds to me that you are describing “cupping” where the edges of the boards curl or raise. This is an indication of a moisture issue. The boards are expanding from excess moisture and pressure. Is this floor installed over a crawl space? I would do 2 things at this point. Go to your nearest electronics store and purchase a little device called a hygrometer, which gives you the temperature and relative humidity of the room. Place it on the floor for an hour or so to get a reading. Run a dehumidifier. If you had a moisture meter, I bet the reading of the floor would be over 9%.

Follow-up Q: The floor was installed over a poured concrete basement. The floor was installed in December, though, and it was not very humid then. Will it ever flatten out or will I just have to live with it? I doubt that the installer would do anything about it or maybe he couldn’t. I had been running the heat and air, however I live in Atlanta, Georgia area and it does get hot and humid here. I will buy a hygrometer and see what it registers. Will the dehumidifier make the boards lie flat again? I have a dehumidifier in the basement, but not the main floor of house where wood is.

A: One never knows for sure if a floor will flatten out. But the sooner you get on it and remove or expedite the transfer of moisture, the better are the odds.

Historic floods and hardwood floors

Q: We have a new wood floor installed in a new addition, over a newly built crawl space. The floor was installed during a very wet period of the summer (historic floods took place near that time). The floor was flat after finishing. We covered it with drop cloths for a few weeks while trim work was done. When we removed the drop cloths, the floors had cupped. There had also been a problem with drainage that the builder had fixed, but not before it flooded the new crawl space. Now we are stumped – the job is done, we are about to have it inspected, and the builder is saying to wait until winter for the floor to flatten out with the heat. What if it doesn’t? What if it still needs to be resanded and refinished? Whose responsibility is this? We are reluctant to move into the space before this issue is resolved, but how long can/should we wait?

A: It seems obvious that the water source is not in question. I don’t think covering the floors with drop cloths for a few weeks was a very good idea since it would not only slow down the curing of the finish, but may impede the normal transfer of moisture that does occur with wood.

It may well have cupped in any case, given a substantial amount of water under the crawl space. I think efforts should have been made to ventilate and dry that area as soon as possible.

At this point, it really is important to allow sufficient time for the wood to adjust and it is possible that it will flatten out once the heating season begins. The problem is, if you sand the floors too soon, they may bend the other way or crown. I think you need to have an agreement with the contractor that if they don’t flatten out during the winter, he will have them re finished. I know moving into the area and then taking everything out is aggravating. But at this juncture, time, ventilation and warmth are the only friends you have.


Q: We are in the final stages of having red oak flooring installed in our home. We chose to have a water based varnish applied vs. the oil to allow more of the true wood colours to show. Prior to application of the water based varnish the floor was smooth and level. Subsequent applications of varnish have resulted in slight cupping in the flooring. The installer has indicated that this is a result of humidity getting into the flooring material. The thing I don’t understand is why didn’t this show prior to the varnish being applied? The project was started in early July with the flooring material having been nailed down in place for two to three weeks prior to the first application of varnish. Prior to that time the installer left the bundles of lumber in our house for 10-14 day so it could become acclimated. Had we been advised that the water based product could result in cupping we probably would have made another choice. What if any alternatives are available to us? The installer has indicated that it (the flooring) will probably “lay down” more later. Could this have resulted from improper application of the varnish by the installer? We have a beautiful but wavy floor.

We moved into this home in Sept-81. The oak plank flooring is installed over ¾ plywood sub floor with a crawl space. The crawl space has heavy plastic over the earth underneath. Prior to the red oak plank flooring we had Ash parquet flooring that was installed in ’81 which gave us no problems.

A: I have known water borne finishes to cause cupping. It is important when using these finishes to vent the area and cause the small amount of water to evaporate away from the floor as soon as possible. This also means allowing time for each coat to properly dry before applying another, and following the recommended spread rate. I would check the humidity in the area, at floor level with a hygrometer, and if excessively high, get a dehumidifier or fan blowing. Heating season is almost upon us, and hopefully, with the furnace running, the floor will flatten out.

Large bubble

Q: There is a large bubble in a click-type engineered floor in our basement. It was installed 6 months ago. The dealer says it is due to excess moisture and will charge for a T cap, removal of quarter round and repair to board. Is this reasonable?

A: Well, I guess one has to ask if any contractor is responsible for the maintenance of the environment year round in a house. If there is any sort of installation in a basement, I always enquire about moisture and humidity. Sounds like you need to have a dehumidifier running during the summer, just like me. I can’t give a better answer because I only have your brief email to respond to.

Buckling floors and blame from landlord

Q: What can cause hardwood floors to buckle in some areas? No water or liquids have been left standing anywhere. The owner of the home is blaming my family and I, since they have occurred after we moved in.

A: Only moisture can cause this. I am not familiar with the layout. It could come from almost anywhere. A crawl space. A clothes dryer not vented to the outside. Water coming in from somewhere and concentrating under the area in question. A leak in a pipe upstairs that runs down a wall and under the floor. You have to be a detective at this point.

Severe cupping

Q: I bought a home in New Mexico (extremely dry climate) three years ago which had been completely renovated. The entire home had been installed with soft wood flooring. The subflooring I believe is wood with a crawl space under the house. I noticed this winter that the floor was severely cupping in certain areas (the onset of which appeared to be quite sudden).

Since moving into the house I have noticed that the house creaks very loudly which appears to occur more frequently during seasons with greater temperature differentials (cold nights, warm days). I’ve wondered whether the creaking is a sign of the house settling and therefore a possible cause of the cupping in the floors.

I did pull up the moulding along the walls closest to the most severe cupping and the there was absolutely no gap between the wood floor and plaster wall – in fact the floor looked like it was burrowing into the plaster along one wall and along the opposite wall was being forced downward so the plank had assumed about a 30 degree angle. I’ve just assumed the cause could not be due to moisture since we have been experiencing the driest winter in recorded history. And there has been no water damage to the floors or in the crawl space.

The only change I have made over the last year is have a wood burning stove installed. Are there other possible causes of cupping floors aside from moisture? Do you have any suggestions? My inclination is to create space between the wood floor and the plaster walls but am reluctant to do that before determining the cause of the cupping. Any advice would be greatly appreciated.

A: The only reason a floor will cup is from excessive moisture and lack of expansion along the side walls does not help at all. Your floor is picking up moisture from some place. I would definitely cut the floor back along the walls 1/2″ at least. A moisture meter and hygrometer could help you to know exactly what the environment is at the floors surface. The moisture source is likely from the crawl space. If the crawl space has a dirt surface, I would place heavy plastic sheeting over it and make sure it is cross ventilated.

Floor might level itself out

Q: Providing I cut back the flooring along the walls and address the moisture issue once I determine it (as you assumed the crawl space has a dirt surface and there was no intentional source built into the crawl space for cross ventilation from what I can determine) will the cupping that has already occurred level itself back out or will I have to level it manually (i.e.- sanding)?

A: The floor might level itself out. I would give it several months to determine if it will adjust itself. If you do have to have it sanded, make sure it is tested with a moisture meter first to be sure it has returned to normal range.