Water Bubbles on New Concrete Floor

9 Replies

I have an apartment that is below grade that had a wooden floor that buckled. We removed the floor boards and found moisture coming up thru the concrete floor underneath. 

The American Leak Detection company came out to check water coming into the house, and no leak was found. No sewer/drain line was checked, however. Thinking that the moisture was a result of badly prepped work, we had professionals take out the floorboard, prepped the concrete, added assailant chemical and installed an epoxy coated floor about 6 weeks ago.

We came back yesterday and saw bubbles in some parts of the new floor, mostly in the same spot where the wooden floor had buckled, but also in other areas where the floorboard seemed to be ok before. The bubbles when popped had water in them.

Any thoughts on what the problem might be or things we should check/investigate?

Account Closed - it seems that you have an excessive amount of moisture in the basement... both the buckling wood floor (I assume wood flooring installed over a sleeper system) and the epoxy floor bubbling are indicative of high moisture.  Curious, was the moisture content of the slab checked prior to installing the epoxy floor?  I'm pretty certain that the epoxy manufacturer has something to say about that and in what applications their product is suitable.

The moisture is possibly vapor (since you didn't mention any flooding), so being trapped by the epoxy floor, it formed bubbles and collected as water.  I would check the moisture content of the walls, concrete floor, wood members in the basement and the air itself - my guess is that they're all reading higher than recommended.

Thank you for your feedback, @Michael Paris

There was definitely lots of moisture on the floor, but unfortunately the contractor didn't check the moisture level after applying the sealant which we realized now was a mistake. But I thought he was the professional and there is a one year warranty on the job, so was surprised he didn't make sure everything was good before going ahead with the epoxy.

So we're trying to get him back here to see what he has to say, but also wanted to do a few test on the drain pipe, just in case there is a leak. 

If you or others have any other thoughts, I would appreciate it as well. We're just hoping to fix this without spending too much time and $$.

May very easily have nothing to do with a "leak".

Concrete is porous, and air, water, water vapor, etc., will travel through it.  A standard demonstration related to this is dropping a chunk of concrete into water -- it will bubble for a pretty long time as it takes on water, then when you take it out the reverse occurs.

Can't really tell -- are you saying this is new construction?  Or a new slab poured in an existing house? How old is the slab?  Often, a slab is not given a chance to dry out from the moisture that results from the initial placement process.  Construction itself can create a lot of moisture.   

Beyond that possibility, it sounds like your have either no below-slab vapor retarder, or the wrong type, or one that has failed.  Below slab treatment is critical, and so often done wrong.  

Also unfortunate -- your contractor's sealing efforts may have made the problem even worse, since it essentially eliminates dry-out for a slab...  once water IS in the slab from whatever source, it can only evaporate upward.  l sometimes think that these sealers work just long enough to give the flooring contractor a decent amount of getaway time.

There are some solutions, but very often in these situations there are flooring types and/or conventional install methods that just aren't going to work .  Sorry that there may not be an easy answer.

@Kurt F. - thanks for the feedback.

It was an old construction, but the seller remodeled and put in hardwood floors. We bought the house almost 3 years ago and not long after purchase, we noticed that the floor started buckling and later popped. So we got a contractor to remove the boards, cleaned up the concrete, sealed it, and put in new concrete/epoxy floor.

So what do you guys suggest for us to do to fix this problem? How do we find the source of problem first of all? Is there a company that I should contact to investigate? We rented this space (tenant is leaving next week) so will have to delay the next one, but wanted to make sure we get the place fixed soon enough.

Thanks again, appreciate your feedback.

Not sure what your area is like. But is it possible that you're simply not getting enough of the water away from the house when it rains?  Or not getting it far enough away from the house.

I personally hate houses with slabs but I have two of them nontheless. Both had water problems.  I trenched all the gutters and did pop outs well away from the house. I also trenched around the sides of the house, added drain tile. filled the trenches in with gravel and tied that in to the same gutter drain tile that goes away from the house.

Lastly, I installed ceramic tile on the slab. Thats about the best you can do in my mind without tearing out a whole bunch of concrete or something crazy to try to figure out the issue.

There's a nice tile at lowes that looks like hardwood provided you install it with no grout lines (still need to grout the ridges between the tile). It works great. Looks good - most tenants think its hardwood until I tell them. And it limits the risk of damage.

At some point, thats the best you can do. The mortar and tile are essentially concrete so that gives you an even higher base of the floor for the water to have to come up. And the other thing it does is that, if you were to get water, the floor wouldn't be damaged nor would you have to deal with a tenant calling you telling you to come dry out the carpet before it gets mold.

You're hoping for a point-source problem -- leaky pipe or something -- and I do hope you can find one.  

But, I doubt that you will find one.  It's probably more or a general problem.  Per my previous post, I'm guessing your below-slab vapor retarder condition is lacking to non-existent.  Probably most of your entire slab area is taking on moisture from below...


How far below grade is the finished floor level?  If it's not much below, you can follow @Mike H. 's advice. 

If it's deeper and modifying exterior perimeter conditions won't help, then it's on to dealing with the problem from the interior.  

You may need to prepare for the possibility that your new epoxy floor will fail.  I know that @Account Closed is correct -- above a certain mositure content, the floor should not have been installed.  

If the epoxy fails, and I hope it does not, one solution is the range of "3D" subfloors that exist.  These created a slightly raised floor above the slab surface that allows a drying space, and the finished flooring material stays dry.  A quality version might be 2 bucks / SF just for the subflooring.  And, you lose a little ceiling height.  And, you need to consider wood walls already in place.  And...   But, it works for some people in some cases.

Thank you so much you guys. Now, since the epoxy floor is already installed, removing it would be challenging. I was wondering if it is possible to put a vapor barrier underlayment right on top of it and then get a LVT as the finished floor?

And @Kurt F. to answer your question, the house is on top of a hill, on serpentine rock. And the unit I was referring to is on the first floor, about 1-2 feet below the grade around the immediate area. The terraced garden in the back area goes up to about 12 feet.

Thank you so much you guys. Now, since the epoxy floor is already installed, removing it would be challenging. I was wondering if it is possible to put a vapor barrier underlayment right on top of it and then get a LVT as the finished floor?

So far you've witnessed what have essentially been two full-scale proof-of-excess moisture experiments, and are very possibly headed for a third.  Probably time to stop guessing. 

Honestly?  I would strongly suggest you have someone with some actual expertise look at the conditions in person -- could be a knowledgable GC, an architect, etc.  

This reminds me of Engineering 101 The basics of hydrostatic pressure regarding cement with an initial high moisture content. As my Prof would say "Such a 'natural system' will tend towards equilibrium for areas of higher or lower relative humidity" & you definitely have a serious case of moisture diffusion.

The relative humidity within the concrete slab is very different than that of the air in the basement room. The 'moisture' that is being absorbed naturally by such a cheap porous slab (that obviously lacks any form of insulation & vapor barrier when poured) is going to wick through the slab. Without a sub-surface vapor barrier, the relative humidity in the slab just below the surface can often be 100%. Since the air in the above room is seldom that humid, moisture is going to constantly diffuse from the slab into the air and as the surface dries it will continue to draw moisture up from the bottom of the slab.

As in your case when the ground beneath the slab is very wet & the slab surface will remain damp, slick and moisture will condense beneath any objects placed on the slab. Furthermore, as the water vapor moves through the slab, it will condense and may leach calcium hydroxide which then ends up as efflorescence on the slab surface. 

But the biggest problem you have with the amount of moisture reported moving through the slab is the pressure it exerts at the surface. ANY impermeable layer (your wood floors then epoxy) placed over it will accelerate the moisture migration resulting in the delamination of any & all overlays. It will also harbor mold growth. So I would try a commercial 'water permeable' sealer:


If that fails I would be tempted to drill a number of sump holes (to allow a larger concentrated diffusion of moisture) around the slab perimeter. This was very effective for the constantly damp basement floor of one of my daughters homes.

good luck

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