We have recently come to a halt with our building due to our hardwood floorboards cupping and swelling in several places.(Boards were acclimatized for several months before installation) They were laid by a so called professional installer, who sealed the concrete first then laid the boards, sanded and applied only one coat of lacquer.

Within a month we noticed boards cupping and swelling!! The installer has no idea of the cause and wanted more money to fix the boards, but not fix the cause of the problem. Since then we have given him the boot!! (unfortunately paid him majority of the money!! and heard nothing from him since!!)

My husband (handyman) replaced the popped up boards and sanded the entire area lightly at first waited another few months then sanded the entire area again. Now are faced with the moisture coming up through the joins as pictured.

Is there any solution? Our next step is an expensive inspector, but unfortunately money is an issue right now. If there's anybody out there that has had this problem or knows how to solve or point us in the right direction would be so helpful.

Beginning of problem. This Happened first before we replaced damaged floor and gave it a light sand beginning of problem

Another pic, repair stage boards replaced and lightly sanded. Within a week of sanding Moisture coming up.

more moisture

like this through the entire house

  • 1
    This looks suspiciously like moisture coming up from below. How was the concrete sealed? Is there any sort of air gap between the concrete and wood?
    – Comintern
    Commented Apr 12, 2014 at 3:34
  • 3
    I am afraid there is no good solution for this, that I am aware of. Well there is but it ain't cheap. If it is rising damp..... It would start with all the flooring coming up. I don't think there is a technology out there that will keep that volume of water at bay without creating another problem, mold....
    – Jack
    Commented Apr 12, 2014 at 4:18
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    What type of flooring is this, what was the moisture barrier with concrete, how was flooring installed, is this area in the middle the only area with water coming up?
    – DMoore
    Commented Apr 12, 2014 at 4:41
  • Thank you so much for your comments: yes the moisture is coming from the bottom only in the joins. the concrete was sealed with acrylic two pack sealer? not 100% sure though. theres no air gaps between the concrete and wood. The floorboards aren't wet when you touch them they just look wet?? The boards we used are called black butt Timber hardwood flooring. It was installed by a so called professional who sealed the concrete slab first. and problem is right through out 124sqm. nearly all the boards not just one area. i have tried to upload more pics but only 2 ended up uploading??
    – Eve
    Commented Apr 12, 2014 at 14:10
  • 1
    If you paid the contractor a considerable amount of money for this work, it may be time to consult an attorney.
    – Comintern
    Commented Apr 12, 2014 at 17:46

5 Answers 5


Your problem is obvious. Moisture is migrating up from the slab. I don't imagine anyone suggested to do a moisture check on the concrete before you started? There are meters that can measure the % of moisture in concrete. With that said, it is never a good idea to put wood or laminate directly on concrete slabs or uncured concrete upper floors. In your case, you said the concrete was sealed. How was it sealed and with what? One of the only products that seals and creates a vapor barrier is DryLoc. Even using DryLoc, some sort of underlayment should be used. The old way was to lay pearlings across the slab, put on a plywood subfloor and then your finish floor. Today there are several subfloor products that resemble 2'X 2" or 2" X 4" panels with a waffled plastic base and a resin embedded or synthetic subfloor attached. These panels interlock covering the concrete and create a vapor barrier. The materials in these products resist mold and mildew and allow any water to escape if you have floor drains etc.

Unfortunately, once hardwood has cupped badly or water stained from the bottom up, it is usually junk and cannot be reused. Sometimes if the cupping is minor, exposing it to a very dry environment for some time will allow it to flatten out, but I sure would not count on it. In your case, I fear you have no alternative but to rip it all out and start from scratch. This time, address the moisture or possible water leak in the concrete first. Use a proper subfloor, or select a different kind of flooring that is not susceptible to damage from moisture. There are several vinyl plank type floors that look like wood or tile that are good choices in a damper area.

  • 1
    I have used the 2x2 panel you refer to, They work very well for applying this type of hardwood floor over a concrete slab. Did it in 2 homes, no problems to know of. The water problem was addressed more aggressively than a topcoat of ...something.... The concrete was broke up around the perimeter, perf pipe set, interior walls treated with solid PVC sheets top to bottom tied into the drain field sealed at the joint with polyurethanes' caulk, etc, etc. THEN the 2x2 panels were glued together that have the waffle plastic on the bottom to use as a fail safe. Redundancy is crucial in this matter.
    – Jack
    Commented Apr 12, 2014 at 23:06
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    Agreed, the root problem of where the moisture is coming from needs to be addressed and cured before proceeding. Commented Apr 13, 2014 at 9:43
  • Thank you all for your help. So basically what everyone is saying is that we need to rip the raw floorboards up?? the first picture i showed was how the problem began but second and third pictures are what they look like now (they are fixed and sanded and just breathing but theres moisture coming up) is there a way to get rid or dry the moisture? we are stuck for cash so re doing them is going to be hard and impossible right now :(
    – Eve
    Commented Apr 16, 2014 at 1:31
  • You certainly can run a dehumidifier in the interim with hopes it may lower the moisture level, but i doubt it will be a long term fix and I bet the problem will come back again and again. The job was not done properly to begin with, so you don't have a lot of options if the contractor won't stand behind their work. Commented Apr 16, 2014 at 9:33

It is possible most of your flooring can be salvaged. I see a small area where it might not be able to but this depends of the install. If the tongue/groove are glued you have almost no chance of pulling the board apart for reuse but if they are just "locked" then you are better off.

The key is that I would under no circumstance lay anything on that floor in the future. You need to have the concrete sealed. Then you need to have a foam/rubber barrier then plywood. The floor will be raised an inch at least - it is a bigger project getting the subfloor in place than the flooring.

That leaves me to a suggestion. You cannot always get exactly what you want in every situation. I would not suggest hardwood or carpet in this area. I would simply seal the concrete with something like dryloc and then install an all vinyl/rubber engineered flooring. Home Depot carries a really good brand of thick vinyl planking that I have installed many times. builddirect.com also has a variety of this flooring - very reputable site.

  • 1
    If it was a standard hardwood installation with hardwood staples–many in each plant, it will be quite laborious to remove them without damage. Even with a modest recovery effort, expect to lose 25–50% during removal.
    – wallyk
    Commented Apr 12, 2014 at 16:29
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    @wallyk - I agree. I just don't think they should think about hardwoods unless they can go like 6 months to a year with proof of no moisture.
    – DMoore
    Commented Apr 12, 2014 at 16:46
  • Looking at the pics supplied, it sure looks like there is substantial cupping across the entire floor. I would not even try to salvage this wood. It is junk in my opinion. Commented Apr 13, 2014 at 9:47
  • @shirlockhomes - probably but you never know until you start pulling. It really doesn't matter because I wouldn't install these in the same home. Might make for a good wall or ceiling though.
    – DMoore
    Commented Apr 13, 2014 at 15:53

This thread is dead, but I know the problem. Condensation. Simple.... Colder concrete than air temp, water condenses on the sealed slab. The dehumidifier would work, if you want to slather on chapstick and lotion all summer. Tile is better on concrete. Period. Vinyl and floating laminate wood floors are for either poor or uneducated people. The very best solution is tile, with ditramat or another form of crack isolation, then use tiles that look like hardwoods...they are expensive, so is the mistake that was made here. Very expensive.

I am a licensed NC contractor, specializing in being on site, swinging a hammer myself, and building one or two totally custom homes a year.


Before you rip out the whole floor you might want to consider renting a dehumidifier first. I had a similar issue last year with my floor and my carpenter had me run a dehumidifier for a few days and the results were successful, so I invested in a good dehumidifier which ran me 400.00. But well worth it in the long run. Good luck!!

Do you have a space around the perimiter of the room? There should be about a quarter inch gap between the wall and were the wood floor ends. That gap is meant to handle the shifting of wood, weather it be due to water, humidity, and/or the house shifting through the years.
  I'm  not saying that would have totaly prevented your situation. I'm just stateing that there is a purpose for that gap, and without it you are Guaranteed to run into these problems sooner than later...carrieing on through out its life unless fixed.

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