Sewage Backup in Your Basement: What to Do and How to Stop Mold

After a sewage backup, keep people and pets out of the area, stop using water, shut off power only if it is safe to do so, document the damage for your insurer and arrange professional cleanup. Sewage carries bacteria and other contaminants, so porous materials it touches usually need to be removed, and the space has to be thoroughly dried and verified before rebuilding. Mold can start growing on damp materials within a day or two, which is why fast, complete drying is the key to preventing a second problem.

Why a Sewage Backup Is Different From Clean Water

Not all basement water is equal. Water from a burst supply line starts out relatively clean. Sewage is in a different category altogether. Water restoration standards classify it as the most contaminated type of water, sometimes called black water, because it can contain bacteria, viruses, parasites and other contaminants from waste lines.

That changes the cleanup. With clean water, many materials can be dried and saved if the response is fast. With sewage, porous materials that were soaked generally cannot be reliably decontaminated, and the people doing the work need protective equipment. It is also why sewage cleanup is not a do-it-yourself project for most homeowners.

First Steps After a Sewage Backup

Safety comes before belongings. Work through these steps in order:

1. Keep everyone out. Keep children, pets and anyone with a weakened immune system or respiratory condition away from the affected area.
2. Stop using water. Avoid flushing toilets, running taps, showering or using the dishwasher or washing machine, since that water may drain straight into the basement.
3. Deal with electricity carefully. If water is near outlets, cords, the furnace or appliances, do not walk into it. Shut off power at the main panel only if you can reach it without standing in water. Otherwise, call your utility provider or an electrician.
4. Document everything. Take photos and video of the water, the affected rooms and damaged belongings before anything is moved or thrown out.
5. Call your insurer. Sewer backup coverage in Canada is often an optional add-on rather than part of a standard policy, so confirm what your policy includes and follow the insurer's process.
6. Call a plumber. Find out what caused the backup, such as a blocked line, tree roots or municipal system overload, so it does not happen again during cleanup.
7. Arrange professional cleanup. Water extraction, removal of contaminated materials, cleaning, disinfection and drying should be handled by trained crews with proper protective equipment.

What Has to Be Thrown Out

Porous materials absorb contaminated water and are very difficult to clean reliably. As a general rule, the following items that were in contact with sewage should be removed and discarded:

• Carpet and underlay
• Drywall and baseboards, typically cut out well above the visible water line
• Wall insulation that got wet
• Upholstered furniture, mattresses and soft toys
• Particleboard and laminate furniture that has swollen
• Cardboard boxes, paper and books
• Food, medicine and cosmetics that were exposed

Hard, non-porous surfaces such as concrete, ceramic tile, metal and glass can usually be cleaned and disinfected. Solid wood framing can often stay if it is thoroughly cleaned and dried, but that should be assessed case by case.

In older homes, be careful before cutting out drywall. Joint compound and textured finishes installed before the 1990s may contain asbestos, as covered in our article on asbestos in drywall joint compound. Testing suspect materials before demolition protects your family and the crew.

Why Mold Follows a Sewage Backup

Once the water is pumped out, the basement can look much better than it really is. Concrete slabs and foundation walls hold moisture for a long time. Bottom plates, studs and the backs of any remaining drywall can stay damp for days. Under those conditions, mold can begin to grow within roughly 24 to 48 hours, and it often starts in places you cannot see.

Mold after a backup is a concern for health as well as property. Health Canada advises that mold in homes should be cleaned up and the moisture problem fixed, since exposure can affect health. People with asthma, allergies or weakened immune systems, infants and older adults tend to be more sensitive. Combined with the bacterial contamination from sewage itself, that makes a careful cleanup important.

Calgary and Alberta Factors to Know

Calgary basements face particular risks. Most homes here have a basement, and many are fully finished with drywall, carpet and framed walls, which means more porous material to lose when a backup happens. Intense summer thunderstorms can overwhelm drainage quickly, and spring snowmelt combined with frozen or partially frozen ground can push water toward foundations. The 2013 flood is a reminder for many Calgarians of how quickly basements can be affected.

The dry climate helps drying once equipment is running, but it does not dry a basement on its own. Concrete in a cool basement releases moisture slowly, and winter conditions can make it tempting to close everything up too soon. Rapid chinook temperature swings can also cause condensation on cold surfaces while a basement is still drying. Moisture readings, not appearances, should decide when the space is ready to rebuild.

How to Dry and Restore the Basement Properly

A good restoration follows a clear sequence:

1. Extract all standing water and remove contaminated debris and materials.
2. Clean and disinfect hard surfaces, framing and the concrete floor.
3. Dry with professional equipment, using dehumidifiers and air movers, and keep the area ventilated.
4. Monitor with moisture meters until framing, concrete and remaining materials reach normal dry readings.
5. Inspect for mold before any walls are closed. Any growth found should be addressed through professional mold remediation under containment.
6. Verify the space before rebuilding. A post-cleanup mold inspection confirms the area is dry and clean, and indoor air quality testing can help confirm the air in the home is back to normal.
7. Rebuild with new insulation, drywall and flooring only once the space has been verified.

What Not to Do and How to Prevent a Repeat

• Do not wade into sewage without protective gear, and never if water is near live electrical equipment.
• Do not use a household vacuum or shop vacuum without proper filtration and cleaning, as it can spread contamination.
• Do not try to save soaked carpet, underlay or drywall.
• Do not run the furnace fan while the basement is contaminated, since it can circulate odours and particles through the house.
• Do not close up walls or install new flooring before moisture readings confirm the area is dry.
• Do not paint over stains that appear afterward. Paint hides mold but does not stop it, as explained in our article on painting over mold.

Preventing the Next Backup

Prevention is worth the effort once you have been through a backup.

• Backwater valve. Ask a licensed plumber about installing a backwater valve on your main sewer line. The City of Calgary encourages homeowners to consider one, and installation typically requires a permit, so check current requirements first.
• Maintain the valve and sump pump. Test them regularly, especially before spring melt and summer storm season.
• Keep drains clear. Do not flush wipes, grease, paper towels or other debris.
• Manage water outside. Extend downspouts away from the foundation and make sure the ground slopes away from the house.
• Store smart. Keep belongings in plastic bins on shelves rather than cardboard boxes on the floor.

When to Call a Professional

Call a professional right away for any sewage backup, regardless of size. You should also call if your basement was cleaned up but still smells musty, if stains appear on walls or baseboards, if you are unsure the area was dried properly, or if anyone in the home develops symptoms. If you are wondering what an assessment involves, our article on what affects mold inspection cost explains how the scope is set. When growth is confirmed, mold remediation after water damage removes it safely and documents that the space is ready to rebuild.

Frequently Asked Questions

How soon can mold grow after a sewage backup?

Mold can begin growing on damp materials within about 24 to 48 hours. That is why water extraction and drying should start as soon as it is safe, and why moisture monitoring is important before rebuilding.

Can I clean up a small sewage backup myself?

A very small backup limited to a hard floor might be manageable with gloves, boots, eye protection and disinfectant, but any backup that reaches carpet, drywall or stored belongings should be handled professionally. Sewage contains contaminants that make thorough cleanup difficult without the right equipment.

Is it safe to stay in the house after a sewage backup?

It depends on how much of the home is affected, whether there is a working bathroom, and who lives there. Keep everyone away from the affected area, and consider staying elsewhere if the backup is large, if odours spread through the house, or if vulnerable people are in the home.

Does home insurance cover sewage backup?

Many Canadian home insurance policies only cover sewer backup if you have added a specific endorsement. Check your policy, document the damage thoroughly and contact your insurer as soon as possible.

Dealing with the aftermath of a sewage backup? Make sure the basement is truly clean and dry before you rebuild. Learn about our approach to mold remediation, call Amity Environmental at 403-667-8264, or reach us through our contact page.