QUESTION: I have quick question about my house, which was built in 1990. The inside walls of my garage foundation are crumbling. The wall against the house is just like new, but the two outside walls are crumbling. I can take a broom and sweep against them every three or four months and it seems like a small layer of cement is coming off them every time. I was wondering if there is anything I can do to prevent this from happening.-- Al Cournoyer
ANSWER: Your situation is a common one with attached garages on newer homes and is typically due to moisture in the garage that attacks the surface of the concrete, causing a condition known as spalling. There may be a few things that you can do to minimize the damage, but regular maintenance may prevent the issue from becoming serious.
Deterioration of the concrete in the short grade beam in your garage is one of the few situations in your home where you have to regularly do minor repairs to keep it from becoming a bigger issue.
Attached garages are unusual areas in homes, as they are not normally heated or air-conditioned spaces, but may be finished or insulated similar to the interior of the home. Because they are attached to the home, they will also be less prone to heat loss than detached garages. This makes these areas very convenient for vehicle and utility storage, and normally eliminates the need for block heaters. But this can have negative consequences related to moisture.
The true cause of the deterioration to the surface of the concrete in your garage grade-beam foundation is from moisture and excessive condensation. This moisture may sit on the surface of the concrete or penetrate this porous material. If enough moisture penetrates the surface in the winter months, it may freeze and thaw continually, causing expansion and damage to the concrete. This can certainly lead to the problems you are experiencing, which may continue or get progressively worse as the concrete deteriorates.
Any time this is observed and loose material is seen on the floor, it should be repaired with a high-quality concrete patching compound to prevent further deterioration. These products are available at home centres and building supply stores and may be easily mixed with water and additives and applied in thin layers to smooth and seal the uneven surface of the damaged concrete. If these minor repairs are done every year in the warm months, it may limit the damage significantly and prevent a major concrete repair.
Preventing condensation on the concrete may be much more difficult than fixing minor damage. The cause of this moisture build-up is the actual usage of the garage. Most of the time, the garage vehicle door remains closed and there is minimal air circulation and moderate temperatures inside. In the dead of winter, this interior garage temperature may be just below freezing, but still considerably warmer than outside. The exterior of the grade-beam foundation will be very cold, while the inside will be cool.
When the door from the home is opened for access to the garage and when warm vehicles are pulled inside, the temperature and relative humidity in the garage is quickly raised. This warm air from the home and vehicles carries considerably more moisture than the freezing outside air and will raise the relative humidity in the garage, often near the point of saturation. Melting snow and ice from the cars on the garage floor will add to the problem.
As the garage air slowly cools down after the vehicle is shut off and the door to the house is closed, the moisture in the air will condense on colder surfaces such as the outside walls, windows and the cool foundation grade beam. This moisture may freeze and build up significant frost, which will melt and run down the walls and top of the grade beam when the garage heats up again. Some will absorb into the concrete.
Since water expands rather than contracts when it freezes, it can cause the surface of the concrete to crack and blister and crumble onto the floor.
A partial solution to this problem is to try to eliminate the drastic heating and cooling of the garage, as much as possible, while minimizing moisture intrusion. The best way to do this is to leave the garage door open for a few minutes after pulling the vehicle inside, after the door to the house is opened, and a few times during the day when the weather is well below freezing. This will allow excess warm, moist air to vent out the large door and allow dry, fresh air to enter the garage, preventing excess condensation on the cold surface of the concrete.
Ensuring that the self-closer and weatherstripping on the door to the house are in good condition will also help prevent warm air leakage from the home. But even with these preventative measures, regular patching and sealing of the concrete surface may be necessary to prevent the grade beam from serious damage that may require costly replacement.
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 e-mailed to the address below. Ari can be reached at (204) 291-5358 or check out his website at www.trainedeye.ca.
trainedeye@iname.com
