Basement floor moisture can be difficult, easy to fix

Hey there, time traveller!
This article was published 13/01/2002 (8639 days ago), so information in it may no longer be current.

Question — We have a 35-year-old home in Westwood, which has shifted a bit, and we have experienced basement floor cracking. During the last couple of years we have several areas in our basement floor where we have efflorescence and deteriorated concrete (pitting or spalling). We recently lifted our carpet in our semi- finished rec-room and we also have efflorescence under some parts of it. Our weeping tiles seem to run during heavy rain in the summertime and we have taken corrective steps to the outside of our home to help heavy rains will run away from the house.

We are interested in installing new carpet and finishing our rec-room but we are wondering if we should do something to reduce or eliminate the efflorescence and concrete deterioration prior to installing new carpeting?

We look forward to your reply and we enjoy your column very much!

— Bruce Roger, e-mail

Answer — The efflorescence seen in Mr. Roger’s house is a fine white powder, which will form on concrete that is exposed to moisture. The efflorescence may be from moisture passing through the concrete from the soil below, from water sitting on the surface of the floor, or from excessive condensation on the surface of the cool concrete floor. The cause may also be a combination of one or more of these sources.

The most positive observation described in the question is that the weeping tiles run, into the floor drain presumably, during heavy rains. The weeping tile is the drainage system on the outside of the foundation that collects excess moisture in the soil and diverts it into the floor drain catch basin or a sump pit. This moisture will then run to the sewer system or be pumped back outside the house, by a sump pump, and be recycled. In many older homes, the tiles become plugged and do not operate properly. In these cases, the excess moisture in the soil may force its way into the foundation or through the floor slab by hydrostatic pressure or through cracks and holes in the concrete.

If the weeping tiles are working properly, they should be draining water from all sides of the foundation. This can be dramatically affected by settlement, soil erosion and changes in landscaping and vegetation around the house. If any of the weeping tile stop draining properly, then excess moisture may be built up on that side of the house and may saturate the soil around the foundation and under the basement floor slab. This may be enough to cause the efflorescence and spalling seen on Mr. Roger’s floor.

The weeping tile in a house this age are likely short concrete tubes placed end-to-end, with small gaps in between, to allow moisture to enter. These tubes create a crude pipe that directs the water into the basement floor drain catch basin. If the tubes shift or move, they may become misaligned and the “pipe” will be broken. This can happen from excess heaving of the basement floor slab and the soil underneath or movement in the soil outside the foundation walls. Sometimes the tiles become broken or crushed, from the same factors. If any of these problems occur, the system will break down, and this may be the cause of the moisture in the floor slab.

The difficult situation is that the weeping tile is almost entirely hidden from view and finding a problem is extremely difficult. It may require excavation on the exterior of the house, and/or breaking up of sections of the concrete floor slab. If defective weeping tile is the problem, it will not improve on its own and may get worse over time. I would not recommend replacing the floor coverings until the cause of the floor slab problems is remedied.

Excavation and breaking of the floor slab is the worst-case scenario and is very expensive and disruptive. After all other possibilities are exhausted; a reputable foundation contractor should be consulted for repair costs and methods. There may also be a simpler cause of the problem and one that I see often, during inspections. Many times homeowners run the laundry drain pipe, air conditioner condensate drain lines, and other drains into the floor drain catch basin. The catch basins weren’t designed to carry these large volumes of water in addition to the rain water from the weeping tile, and often become damaged or deteriorated. If the concrete around the catch basin erodes, the water from these sources may go into the soil underneath the floor slab, rather than into the floor drain and sewer, as designed. This large volume of water may cause the problems described by Mr. Roger.

The floor drain catch basin should be inspected by removing the cover or grate and shining a flashlight inside. The concrete at the bottom of the catch basin should be probed with a screwdriver to see if it is damaged. Many times the screwdriver will easily sink into the soil around the drain pipe, due to deteriorated or washed away concrete. Sometimes the screwdriver is not even required, as the eroded soil can be seen with water sitting on top, around the drain.

If this situation is found, the catch basin concrete should be patched immediately, and the washer drain pipe, if present, relocated to a proper plumbing drain. The efflorescence on the floor may be cleaned and the weeping tile ends in the floor drain inspected after the spring thaw and rains to ensure they are working. If everything improves over the summer and fall, and the soil under the floor slab is allowed to gradually dry, then renovation may be attempted.

Ari Marantz is owner/inspector of Trained Eye Home Inspection and is the P. R. Rep. for the Canadian Association of Home Inspectors- Manitoba (www.cahi.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.

trainedeye@iname.com