Renovation & Design

Multiple ways for a house to spring a leak

QUESTION: My son bought a house last June. In his basement, on the freshly painted south basement wall, there are five or six pinholes weeping reddish-brown water on the chimney side of the house.

The house is approximately 70 years old, with a new addition two years ago. The first time it leaked last July it was at the bottom, about a foot off the ground. We patched it up with tar and it stopped. Now he has streams of this reddish-coloured liquid dripping down the walls.

Any idea what this is? Also, the furnace is a 1980 Bryant, high-efficiency, vented through the chimney, angled very low about eight feet from the chimney. The chimney was filled with ice, near the top, in cold weather. I noticed water dripping down the cleanout of the chimney. I'm wondering if this could be the problem causing the seepage in the concrete.

Thanks, Larry Shelest


ANSWER: The colour and location of the water seeping into the basement gives me very good clues to the entry point, but will not identify the whole picture. The chimney ice may be another source of moisture entry but is not likely related to the other problem. I'm glad you included the information about the furnace and chimney, as that situation will also need attention to stop the moisture intrusion.

The small "pinholes" you are describing are a common source of basement seepage, known as snap ties or form ties. These holes are created when small metal rods embedded in the concrete rust through. These thin metal rods or wires have been there since the foundation was poured, as they are remnants from metal ties that held the wooden forms together while the concrete was poured. Once the concrete is sufficiently set and the forms are removed, the ties are cut off roughly flush with the surface of the foundation wall. The exterior of the concrete foundation, including the remainder of the form ties, should have been covered with damp-proofing prior to backfilling to prevent water seeping into the porous concrete.

Foundation leakage can occur, usually after several decades, when the damp-proofing wears out and ground moisture causes the metal form ties to corrode. If this corrosion is severe, the metal will essentially disintegrate, leaving a small round hole penetrating through the foundation wall. During spring thaw and heavy rains, water will seep into the small holes and may leak through into your son's basement. The reddish colour is normally due to rusting of the steel wires, but may also be from dirt or soil washing through from the exterior.

You had the right idea when you tried to plug the holes from the interior but tar or asphalt cement will not last. To properly fill the holes, you may have to drill, chip, or grind out some concrete and metal and then patch it with hydraulic cement or other pre-mixed cement patching compound. In many cases, this will stop major leakage, except during the most severe weather.

Unfortunately, this is not normally a permanent fix, especially if the holes are larger. Injection with epoxy may be the next step, but can be fairly costly if there are several holes. Money may be more wisely spent on exterior excavation at that point, so all the holes can be properly covered with a membrane to prevent moisture entering the foundation wall.

There's a chance some moisture is penetrating the foundation wall from the melted ice forming at the top or inside the chimney, but that is not the underlying cause. The soil outside the foundation can contain significant amounts of water, especially during summer thunderstorms or on warm spring days. This moisture can force its way into the foundation, and any cracks or holes, through hydrostatic pressure. This may be the most common reason for basement leakage. Shovelling snow away from the foundation and extending your downspouts may be the only other way to minimize the seepage without major repairs.

As far as the furnace and chimney are concerned, stopping the ice formation may require an upgrade to the entire system. I think you have erred in calling the furnace high-efficiency -- it's likely a mid-efficient model that still exhausts through the older chimney via a metal vent. Many of these mid-efficient furnaces have problems with ice formation near the top of the chimney, especially as they get older.

If your son's furnace is more than 30 years old, it's time to upgrade. It's exceeded its typical life expectancy, and the exhaust fan that blows the combustion products up the chimney is probably not working properly. This exhaust will cool too quickly, before it exits the top of the chimney, and the moisture it contains will condense and freeze. This can continue throughout an entire winter. When the weather gets warmer, this ice will melt and run back down the chimney and into the basement, often through the cleanout.

Modern high-efficiency furnaces normally vent laterally through plastic pipes exiting the foundation or exterior wall, stopping the ice formation. If the water heater is electric and not vented through the chimney, the older chimney flue can be sealed at the top and bottom and no more ice and leakage problems will occur.

It's likely the newer paint on your son's foundation wall covered the visible signs of seepage through the older form ties, but that will not stop it from reoccurring. The reddish stains are from the water and rust bleeding through the paint during times of high soil moisture. While this is unrelated to the chimney moisture, both a furnace upgrade and foundation repairs are needed to permanently stop the leakage.


Ari Marantz is owner of Trained Eye Home Inspection Ltd. and president of the Canadian Association of Home & Property Inspectors -- Manitoba ( Questions can be emailed to the address below. Ari can be reached at 204-291-5358. Check out his website at



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