Damp floor in the garage damaging home

Hey there, time traveller!
This article was published 16/03/2008 (6410 days ago), so information in it may no longer be current.

QUESTION — I live in a house built in 1975. At the front corner of my attached garage the concrete floor, along with the concrete wall against which it abuts, is always damp. The result is that the concrete at the front of the house, just below the Tyndall stone on the front of the house, is beginning to break apart. I believe the freeze and thaw of winter and spring is causing this breakup as the water turns to ice and back to water.

I am not sure where this moisture is coming from, unless it is draining into the garage after a rain or dripping off the car when it is in the garage. The garage is not heated. Any suggestions?

— Spencer Schell, e-mail

Answer — Your question is very timely, as the recent warm weather is beginning the annual spring thaw. Water in garages at this time of year is very common, but not as frequent with attached garages like yours. I will try to offer a couple of possibilities for the source of the moisture and provide some suggestions to minimize this problem.

The source of water intrusion into homes, attics and garages can sometimes be obvious, while other times quite insidious. You have identified one of the most common causes, which is melting snow and ice from the underside of vehicles. This is particularly of concern with attached garages like yours, as the interior temperature may be several degrees warmer than the outside. Snow and ice that adhere to the underside of vehicles and on mud flaps will often melt slowly and drip onto the garage floor. If the front corner of your garage floor is lower than the middle, which is typical after several years of heaving/settlement, this melted snow may refreeze as it hits the colder grade beam at the outside of the garage. It may also leak into the gap between the floor slab and grade beam, where it will expand as it freezes and thaws, as you have suggested. This is definitely a possibility for the concrete damage you are seeing, but may also be preventable.

If you see water stains and trails on the concrete floor slab that suggest melted vehicle snow is an issue, there may be a couple of things you can do to prevent this from damaging your grade beam. First, knocking off snow from the underside of the vehicles and shovelling it outside will reduce the amount of snow melted. Also, having a mop and pail handy in the garage to collect this water before it drains to the problematic corner is a good idea. Finally, regular caulking of the gap between the floor slab and grade beam with a flexible sealant may prevent any standing water from seeping into this gap, where it can do the most damage.

The next possibility for the moisture intrusion and damage is from the exterior of the garage. The two issues to address here are grading and drainage. If the eavestroughs and downspouts empty directly onto the grade beam, driveway or the ground near this corner, they may allow too much water to collect in this area. If standing water is seen in this location after rains or from melting snow, it may leak into the area under the slab. A simple downspout extension pipe, routed two to three metres away from the building, may solve this problem. Also, snow piled up against the garage walls or grade beam in this area should be quickly removed, as it can run inside the garage as it melts, especially this time of year.

As far as grading is concerned, it is very common for the soil at the sides of homes and garages to settle, especially after many years. This can also happen to your driveway, as normal erosion may cause one area or side of the concrete to settle more than the rest. I would guess that the problem corner of your garage is the low point in the grading on this side of your lot, allowing water to drain from the surrounding area. The solution to this phenomenon may be to bring in more soil and build it up around the foundation. This soil should be packed down to provide a gentle slope away from the home and garage and covered with new sod or grass seed to prevent washing away. Care should be taken to build this soil up in such a manner as to route surface moisture towards the front street and not towards the rear of the home, where it may build up along the house foundation walls. This is a regular maintenance item on almost all homes in our area and can have surprisingly positive results in reducing moisture intrusion into homes and garages.

Other than being a nuisance inside the garage, this excess moisture is causing a minor problem that may become much more significant over time. Water damage to the surface of the concrete of your garage’s grade beam may initially cause some flaking and spalling, as you have observed. With prolonged exposure, this may cause weakening of the concrete as well as rusting and swelling of the rebar inside this short foundation wall. If this occurs, it may lead to structural damage to the garage walls above and precautions must be taken now to prevent this from progressing any further. As soon as the ground is dry and the temperature warm enough, any loose concrete in the damaged area should be removed and the concrete patched. This can be done with any high-quality concrete patch, but may require small wooden forms to be constructed if the deterioration has progressed beyond surface spalling.

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 or sent to: Ask The Inspector, P.O. Box 69021, #110-2025 Corydon Ave., Winnipeg, MB. R3P 2G9. Ari can be reached at (204) 291-5358 or check out his new website at www.trainedeye.ca .

trainedeye@iname.com