Why under-slab drains are their own problem
Slab-on-grade houses sit directly on a concrete foundation, so the drain lines from kitchens and bathrooms run through the soil beneath the floor before they leave the house and join the lateral. In many homes built from the 1950s through the 1970s, those under-slab lines are cast iron.
Cast iron can last a long time, but it wears from the inside. Scale builds up, the bottom of the pipe can erode into a rough channel, and cracks or holes can form. Under a slab, the damage is out of sight and the usual fix of digging down to the pipe means going through finished floors, which is why the options deserve a careful look.
Signs the trouble may be under the slab
Opening the slab compared with working from inside the pipe
Cutting or tunneling
- Exposes the pipe so it can be replaced with new pipe
- Cutting the slab means removing and restoring flooring and concrete
- Tunneling goes under the foundation from outside, avoiding the floor
- Allows slope problems to be corrected
- More disruption to the household during the work
Lining from inside
- Forms a new pipe inside the old cast iron
- Little or no work inside the living space
- Needs the old pipe to be intact enough to line after cleaning
- Branch connections must be reopened from inside
- Does not change the existing slope
What each approach disturbs
| Approach | Inside the house | Outside the house |
|---|---|---|
| Cut the slab | Flooring, concrete and sometimes cabinets or fixtures | Usually little |
| Tunnel under the foundation | Usually little | An access pit beside the house and a tunnel under it |
| Line the existing pipe | Access at cleanouts or fixture openings | Possibly a small access point |
| Reroute the drain | Depends on the new path, often through walls or ceilings | Depends on the new path |
Questions for an under-slab drain repair
- Which part of the under-slab line is damaged, and how far is it from the nearest access point?
- After cleaning, is the cast iron sound enough to line?
- If the slab is cut, who restores the concrete and flooring, and is that included?
- Would tunneling or rerouting avoid the living space in my layout?
- Does this work need a City of Fullerton permit and inspection?
Common questions
Is under-slab cast iron the same as a slab leak?
The term slab leak usually refers to a pressurized water line leaking under the floor. A failing drain under the slab is a sewer problem, though both can cause damp floors.
Do I have to move out for an under-slab repair?
It depends on the method and which rooms are affected. Lining and tunneling often keep work out of the living space; cutting the slab may make rooms unusable for a time.
How do I know if my under-slab pipe is cast iron?
A camera inspection shows the material, and the age of the house is a strong clue. Many 1950s to 1970s slab homes in Fullerton have cast iron under the floor.
General information for Fullerton, not a quote or professional advice. In an emergency, call 911.