Interesting CMU Wall Problem 5

[Einsteim]

I have a client with an interesting CMU deterioration issue. The wall is a basement wall and adjacent to the garage. The wall does see some moisture from the exterior as well as vehicles with melting snow. There is a potential for some salt infiltration, again melting off the vehicle parked in the garage. The house is located in northern Michigan and constructed in the early 70's.

The surface at the garage side (Pic's 2 & 3) has the worst surface deterioration and the basement side (Pic's 5 & 6) is not as bad. The basement side also has a very fine, almost spider web like dust collecting on the surface. when enough collects in a given spot, it falls to the floor below and is a dust basically. The mortar joints are intact and look very good. The block in question seem solid and intact as the sledge hammer suggests when applied quite aggresively.

My suspicion is something in the block itself is working its way to the surface creting the spalling. Cement, or maybe one of the fine aggregates, or another admixture used? The block were fabricated in the early 70's in northern Michigan.

Any assistance is appreciated.

 

[concretemasonry]

From a quick examination, it looks like a classic case of eccessive "Michigan salting", no or poor drainage from the slab and accumulation of salt in the foundation wall. I never understand why people build garages without any provisions for drainage, especially in northern climates with excessive salt in some areas and the common use for washing cars. - After previously living in Michigan, I understand the salting principal and the need for new car sales.

If the garage is cold enough for freezing, there could be repeated cycles of freezing/thawing and periodic supply for salt and moisture from the car and road salt. In time the salt moved through the units aided by the supplied moisture. Even summer rainwater contributes to the distribution of the salt through the system.

The deterioration appears to be erosion of the surface cement paste, exposing the aggregate. In the basement, the problem is not compounded by the freezing/thawing and the process is simply migration of the salt laden moisture to the surface and is deposited at a dry salt (efflorescence).

I assume the basement does not have any drain tile (exterior or interior) since there was apparently no real attempt at moisture control/drainage in the garage.

It looks very similar to a townhouse I recently bought that had poor garage slab drainage and a setting floor slab. Since there is no basement and the block are sound (even without using a sledge hammer), I have no structural concerns since the eroded block are still many times stronger than the 2x4 frame wall bearing on it.

Dick

 

[diarmud]

I believe concretemasonry is correct. You may get away with sealing it.

We are in NY State, near Buffalo. Our house was built in '77. It's a split level with garage over the top floor of bedrooms. Salt is heavily used.

Last summer, a receptacle in the garage started sparking when I plugged in an automotive light.

I opened it up and it was corroded everywhere. I checked the garage lights and other receptacles and they were the same. That is where the Main Panel box is and I checked it but it was fine (no corrosion).

I surmise the salt from parking the cars in the garage caused the corrosion and scale.

I replaced the outlets and switches.

Good luck.

 

[BAretired]

It looks like a sulphate attack. It could be coming from the soil. In Alberta, sulphates in the soil range from negligible to high. Most engineers here specify sulphate resistant cement for any concrete in contact with natural soil.

It may be worthwhile having it chemically tested to see what kind of salt you are faced with.


Best regards,

BA

 

[concretemasonry]

Sulphate attack?

Sulphates are very rare in northern Michigan and the cement availibility is not good because of the rarity and the logistics, even in the 1970's.

How does that fit into the symptoms in the two different areas and the different conditions.

Sulphates rarely get into above grade concrete and are not recommended for concrete masonry units, since the units are produced locally using local aggregates and for local conditions.

dick

 

[BAretired]

If the soil around the foundation is wet and it contains sulphates, the sulphate laden water can rise above grade in the capillary pores of the concrete and exhibit this type of behavior. I don't know whether Michigan has sulphates in the soil or not, but it might be something to check.

Best regards,

BA

 

[Ron]

Is the masonry wall against soil? If so, it looks like typical slow moisture migration and freeze-thaw damage. Could be sulfate attack, but that is usually more likely in contact conditions, not this condition.

The white residue/powder is likely calcium carbonate, an efflorescence resulting from moisture migration through cementitious materials (masonry, concrete, stucco, mortar, etc.

Stop the moisture and you'll likely stop the problem.

You can get the residue analyzed (SEM/EDAX, X-ray Fluorescence, or X-ray Diffraction) for a couple of hundred bucks, then you'll know. If you want to see if the residue contains sulfates, collect as much of the residue as possible and heat it in a small pan. If it contains sulfates, you'll likely detect a slight sulfur odor. If you have access to a pH meter, dissolve the residue in water and check the pH. If the pH is less than neutral, you might have sulfates because a reaction would produce a weak acid; whereas, in general cementitious materials will have a higher pH.

 

[Einsteim]

Ron:

Yes it is a basement wall therefore it does have soil on the exterior side. The exterior side also happens to be under the garage slab, so the potential for moisture from the garage floor (vehicles with melting snow) is likely quite prevelant.

The block does seem sound, at least what remains, so I also believe we need to stop the moisture and that will prevent any further deterioration.

Thanks to all responding.

 

[conceng]

It is possible for there to be two separate mechanisms at work here. Is it a heated garage? If not, the garage side could be freeze-thaw related, initiated from condensation accumulating inside the surface of the wall during the winter months. The moisture will tend to want to go the other direction during the summer months.

Your description of the efflorescence on the inside of the wall would be from moisture migration through the wall, carrying alkalies or soluble salts from the soil, or the inside of the CMU's, to the surface. The distress in the basement may be alkali-carbonate or alkali-silica reaction, where the accumulation of alkali salts at the surface is beginning to react with the aggregates.

It seems as though most are discounting the possibility of sulfates, but it doesn't take a high concentration of sulfates in the soil to create a high concentration of sulfates at the surface of the CMU after 30+ years of moisture migration.

Gregory A. Johnson, P.E.

http://www.midwesttestinglabs.com