QUESTION: I read your column every week and find it informative. The problem I have is the cement on my basement walls is flaking off. I can scrape it off with a paint scraper.
I've had a contractor look at it, and he thinks it may have frozen when it was poured or it is just a bad mixture. An engineer looked at some photos and said it looks like moisture is getting into the walls. They are looking into whether the cement can be sealed somehow.
The house was built in 1973 and I purchased it six years ago, in the spring before the snow was gone.
The home inspector did not note this in his report.
I would appreciate it if you have any suggestions.
Thanks, Rick Switzer, Neepawa
ANSWER: I agree with the engineer who looked at a picture of your foundation walls: Moisture is to blame for the flaking concrete. There may not be any easy way to repair this problem, but if you let it go on too much longer, the consequences could be much more serious.
Without having the benefit of a site visit, which the contractor had, I would only have one conclusion for the cause of your problem. As long as there are no major cracks or other defects visible, moisture intrusion from the soil outside your home is the likely cause of the damage. The term "spalling" is often used to describe the defect you are seeing in your foundation walls. This occurs from deterioration caused by moisture. This moisture could be from penetration through the surface of the concrete, as would occur on a sidewalk or driveway, or from moisture moving through the concrete. In your situation, there should be no large source of moisture on the interior side, so the moisture must be coming through the wall.
Many people do not know most untreated concrete is quite porous. Without proper sealing or waterproofing, it will readily absorb water. If the concrete is located in a well-ventilated dry area, this may not be a major concern. For example, if your concrete driveway is well-constructed, has a good granular base and good drainage, it should easily dry after a heavy rain. This will prevent the slab from becoming saturated and remaining wet for an extended period of time. If these conditions are not favourable, or if you have major cracks in the surface, the concrete can remain wet long after precipitation occurs. In the worst cases, this moisture can cause the cracks to expand and the surface to spall.
I understand the contractor's assertion that surface spalling can be due to poor conditions at the time the concrete was poured, but this does not apply in your case. His explanation would only apply to newer concrete where this phenomenon is seen. Your foundation walls are almost four decades old and damage due to a bad concrete job would have been more severe and shown up a long time ago. For this reason, I will dismiss his suggestions and give you mine.
All concrete foundation walls in homes built in our area must be protected from moisture at the exterior. This protection may take several forms and is normally called damp-proofing. The most common method is to take a bitumen-based coating and apply it to the concrete all the way from the footing to grade before backfilling. This thin barrier will prevent the porous concrete from wicking moisture from the damp soil. The problem with traditional bitumen foundation coatings is they have a limited life expectancy. Over a period of 30 to 40 years, which is the age of your home, they may wear out. When this occurs, the concrete will again be able to absorb moisture from the soil. This is what is undoubtedly happening in your home.
If the concrete in your basement has good ventilation and your house has low relative humidity in the air, the absorbed moisture in your basement walls may evaporate through to your basement and cause few problems. When the conditions in your home do not allow this to occur, or if the concrete is continually made wet by the soil, the moisture may remain in the foundation walls.
This water will still try to force its way out of the concrete, normally to the side with the least resistance to evaporation. Often, this will cause the surface of the concrete to spall as the water vapour attempts to escape. The surface concrete will be literally pushed out, creating the conditions you're observing. Often, this is accompanied by lots of efflorescence, or white chalky powder, appearing on the surface.
For the reason stated above, applying any interior sealers or repairs may be futile. If you try to seal the interior surface of the concrete, and it still remains wet and the sealer will either flake off or cause even more damage to the wall.
The real solution is to stop the water from getting into the concrete in the first place. This can only be accomplished by reducing the amount of moisture in the soil and damp-proofing the outside of the foundation walls.
The moisture can be minimized by replacing the weeping-tile system, which may be blocked and rendered ineffective. To accomplish this, the foundation must be excavated all the way down to the footings. Once the soil is dug out, the old exterior weeping tiles -- if they exist -- can be removed and replaced with modern plastic drainage piping. This allows the foundation walls to be covered with a new membrane, preventing further absorption of water from the surrounding substrate after backfilling.
While this job is labour-intensive and costly, it may be the only effective way to dry the foundation and stop the deterioration. There may be some more innovative and less-costly ways to dry the concrete without excavation -- one recently developed by a hardworking local entrepreneur -- but we'll leave that for a future discussion.
Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the president of the Canadian Association of Home & Property Inspectors -- Manitoba (www.cahpi.mb.ca). Questions can be emailed to the address below. Ari can be reached at (204) 291-5358 or check out his website at www.trainedeye.ca