How to fill a deep concrete void under a slab or wall
Deep, hard-to-reach wall and slab voids make it difficult to pour or pack material all the way to the top without leaving empty gaps. Without a proper method to squeeze the mix in, the cavity cannot be filled to the brim, leaving the structure vulnerable to sinking.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
- 1Using high density expansion foam as a DIY fix
- 2Building a hopper and pouring liquid grout into the void
- 3Hiring a mud jacking professional
- 4Selling the house
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
r/homeowners1 person · September 2026
“Found a hole under my driveway and stuck a stick in to see how deep it was. I could stick it all the way in (about 80cm) and wave it around underneath the slab. What can I fill the void with before it starts sinking?”source ↗
maximumfacemelting · r/homeowners · 16 upvotes
r/HomeImprovement1 person · September 2026
Where this came up
People with this problem also raised
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- 4How to fill a wide gap between garage floor and driveway