"concrete smell"

Some 20 years ago, I built an addition onto my house. It is built on a concrete slab with 42 inch block foundation. I have a completely finished room in which I have installed ceramic tile flooring. Under the ceramic tile I used Ardex to level the concrete before tiling. 
For the last 20 years I have never noticed what now appears to be a "wet mortar joint" smell.

I have become increasing alarmed about the slab leaching moisture into the room. There is no visible sign of moisture. The tile is not exceptionally cold; it's just that smell. 

Can anyone put my mind at rest, or suggest to me what this might be and how to remedy it. I definitely can not destroy the floor.

Please advise.

Thank you.



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canucksgirl2 years ago

Can I put your mind at rest? Unfortunately no. Concrete is porous and even a dry looking slab will have some moisture that is seeping through and evaporating into the air. A simple test is to tape down a 2' x 2' sheet of plastic for 24 hours and see how much moisture is collecting beneath it. In this case, I'm afraid you've created a very large "test" surface by installing the ceramic flooring, which is inhibiting the ability for the concrete to "breathe" and is causing this odor.

If the slab wasn't installed with adequate drainage (usually crushed rock and a weeping system) and a waterproof membrane, the best method for flooring is to install it over a floating floor that has a dimpled or corrugated underside that allows the concrete to breathe and the moisture to evaporate.

The fact that you've clearly stated that you cannot destroy the floor will limit your options. I can almost guarantee there will be no way to reduce the smell or change what is occurring below the tile. Over time I'm afraid you may run into mould issues.

moea (author)  canucksgirl2 years ago

Thanks for the reply. I just wished it had been better news. The concrete was poured with crushed rock and has about a 3 foot styrofoam insulation along the perimeter, but NO waterproof membrane. As to a weeping system; I'm not quite sure what you mean. Are you suggesting there should have been "piping" from under the gavel base? There is a perforated pipe from the downspouts around the perimeter. Could something be done around the outside perimeter to correct my problem?

The concrete was pored about a year before construction of the room. The smell has not been present for the past 20 years. Even though we've had a relatively dry season, I began to smell the odor only about 1 month ago. It has really effected my sinuses, makes my eyes dry, and I can't be in the room for more than a half an hour.

Since I have "limited options", can you suggest what options I might have? I suppose I could have the tile floor removed, the rough surface smoothed and new flooring installed. As you can see, I would really prefer not doing that, but if you suggest that as an option, what else would I need to have done to do it properly and avoid a re-accurance? Where does the concrete moisture from a corrugated underlayment evaporate to? Wouldn't the smell persist?

Would you all recommend I first have a home inspector do some testing? Maybe to see if I do have mold. What other testing would you suggest? Would it be worth removing tile and drilling through the concrete to determine it's condition and contributions?

Any further suggestions would be greatly appreciated.

Thanks.

It sounds like you have adequate drainage around the foundation, therefore I don't think there's anything more you could achieve from the outside. I believe the problem is caused by condensation. You have a concrete slab sitting atop rock and earth that is much colder than the inside room temperature. When cold and warm zones meet, they create condensation. (Imagine a single pane window on a cold winter day). Prior to installing the tile, water vapour was simply evaporating into the room (because there is no vapour barrier beneath the slab). A dimpled or corrugated, vapour barrier underlayment will create an insulating break of air between the two zones. Any residual vapour is able to escape the perimeter of the room (because its installed like a floating floor).

If you want to try testing for moisture, you could tape down some thick poly (used as vapour barrier for insulation etc) directly over the tile and see if you have any dampness after 24-48 hours. Even though the tile is slowing the rate of evaporation, the tile itself isn't water, or vapour proof, and its still allowing some moisture to escape (thus the smell), so its a simple enough test to do without removing any tile, or drilling any holes (which I don't recommend).

In terms of fixing the problem, you really should determine if its merely an odor issue (caused by accumulated moisture that's now stagnant), or if its a health issue, like mould. If its mould, you will want to take professional advice in removing the tile and cleaning the slab. That will require proper ventilation, safety gear and preventing mould spores from contaminating other parts of your home. Its not worth getting sick over.

If its only an odor problem and you have enough room height, you may be able to install a dimpled, vapour barrier underlayment over the existing tile and then install new flooring over that. If you have the right underlayment and its installed correctly, odors should not pass through either. Just ensure the product you use is a dimpled (or corrugated) vapour barrier and its installed with no holes or it will compromise its ability to act as a water vapour barrier.
moea (author)  canucksgirl2 years ago

canucksgirl:

When I mentioned I had drainage around the perimeter, I wasn't specific enough: I have black perforated pipe about 1 foot deep from my downspouts. It is not laying in a gravel bed and is not in a sock.

I've contacted a building inspector and having him cone out to advise me and maybe do a mold test.

I think I'm inclined to remove the tile floor and get down to the concrete. I'd start over and use a vapor barrier. If I get the concrete smooth, should I use some sort of primer as an added insurance, then apply the vapor barrier? I see there is a product made in Canada from Delta-fl that looks pretty good. I'm not sure what the corrugated membrane looks like. Our Homedepot has a 3 layered product the folds out as sheets. Would that be it?

I'm really getting more distressed everyday about this project. I guess this is another example of don't always do the project yourself. But, then again, I didn't do the concrete slab, but should have probably consulted an architect before doing the project.

Thanks for all your time and advise.

Ideally you want your perimeter piping to be socked and on a gravel bed to ensure the drainage holes don't get clogged and to avoid water pooling. Older homes merely had clay pipes and as long as they weren't broken, they were still sufficient in keeping water from the foundation; so its difficult for me to say if your situation is okay as-is or not (IMO, it sounds like your piping is too shallow).

The Delta-fl is definitely a good option (its available in the U.S. too, since I don't know where you live); but you can use any product as long as it can be installed air-tight (with an airspace between the product and the concrete). If the joints can allow air (or water-vapour) to escape, then so will the smell. The Delta-fl is installed with the dimpled side down, with moisture-proof tape to seal the seams (sold by the roll, no longer available in sheets). Around the perimeter, you'll want to take the poly (that should be covering your insulated walls) and lay that over the flooring product and seal it down with an adhesive-sealant). That way the floor wraps up with walls and your room is completely insulated from the colder zone outside. The product at Home Depot may be okay (not sure what product it is), but I would suggest you inquire about their claims (they should have a spec sheet about testing and how air-tight their product is) and what's offered in respect to warranties. Many so-called "water-proof" products still allow a considerable amount of water-vapour to escape (such as those cans of roll-on concrete "sealers").

I certainly understand your concern, but don't beat yourself up over doing things yourself! We're all DIY'ers here. Plenty of people have followed building codes and run into problems later on, simply because some codes are inadequate and they fail to tell you that additional, sometimes inexpensive measures can save you many thousands later on.

If the drainage around the slab is working fine you should find moisture under actual slab.

If possible you can try to dig out some dirt from under the slab to confirm it is dry and not smelly, best from different sides.

This would leave the problem (if all is dry) to the sealed concrete and temperature differentials.

I suspect that moisture causes a reaction between the concrete and the tile adhesive, maybe even some mould forming.

You can do the thermometer test:
Either use an infra red thermometer or a bunch of cheap standard ones and check the temp on various spots on the floor - it should be even.

Uneven temps mean areas of moisture and dry areas, usually a sing of broken downpipes near by or under the slab.

To get rid of the smeels for good you only have the option to remove the tiles, install proper insulation and put the tiles on a floating floor made from cement sheeting.
Of course the concrete would need to be dried out and sealed before starting again.

Kiteman2 years ago

How long has the smell persisted? It may just be your most recent work you are smelling, and it can last for days or weeks as it cures.

I had similar smels under my extension once the draught was gone here a few years back.

With the kitchen right next to it we suspected leaking water from the pipes there.

Turned out to be perfectly fine, but the pipes in the ground from the gutters on the roof had developed cracks from tree roots and the movibg ground.

The concrete itself was fine (30cm thick slab) but always moist, causing a weird smell.

Some days it was almost like mould on other like you just mixed fresh concrete.

If you have an area where you remove a tile and drill a hole through the slab you can check for moisture:

If the concrete dust becomes clumpy and wet while drilling it means your slab is "floating" on some water under it.

If the concrete is dry but once through you only get mud on the drill you have water being drianed away under the concrete - this is the easier bit as it does not take that long to dry once fixed.

But if the drill only produces dry dust but a lot of smell i the top few cm of drilling it could mean the stuff that you used to level got conaminated and developed mould.

This can sometimes happen if either the concrete or the levelling stuff itself was not fully cured and dry when the tiles sealed the floor.

If you have pipes running near, under or even through the concrete check them first, a tiny crack at a joint can slowly flood a huge area under concrete.

I had similar smels under my extension once the draught was gone here a few years back.

With the kitchen right next to it we suspected leaking water from the pipes there.

Turned out to be perfectly fine, but the pipes in the ground from the gutters on the roof had developed cracks from tree roots and the movibg ground.

The concrete itself was fine (30cm thick slab) but always moist, causing a weird smell.

Some days it was almost like mould on other like you just mixed fresh concrete.

If you have an area where you remove a tile and drill a hole through the slab you can check for moisture:

If the concrete dust becomes clumpy and wet while drilling it means your slab is "floating" on some water under it.

If the concrete is dry but once through you only get mud on the drill you have water being drianed away under the concrete - this is the easier bit as it does not take that long to dry once fixed.

But if the drill only produces dry dust but a lot of smell i the top few cm of drilling it could mean the stuff that you used to level got conaminated and developed mould.

This can sometimes happen if either the concrete or the levelling stuff itself was not fully cured and dry when the tiles sealed the floor.

If you have pipes running near, under or even through the concrete check them first, a tiny crack at a joint can slowly flood a huge area under concrete.