ASK THE INSPECTOR: Mudjacking might not remedy sinking floor

Hey there, time traveller!
This article was published 19/05/2012 (4896 days ago), so information in it may no longer be current.

QUESTION: I live in a bungalow on riverfront property on Henderson Highway, outside the Perimeter. The house was built in 1978 and, to the best of my knowledge, the basement walls are on piles, not footings.

Since the ice jams on the Red River, the worst being in 2009 and again in 2011, the basement floor has sunk almost three inches in places and less in others. This has caused major damage to interior basement walls and drywall ceilings.

In the fall of 2011, I contacted Muddruckers and Poly-Mor Canada, both of which can lift the slab back to its original level. I have not yet done this as I wanted to see if the slab would drop more this spring. Before proceeding I now have concerns that when materials are injected under the slab it will integrate with the existing pea gravel and mess up my under-slab drainage, which is not working that well anyway.

I would appreciate any information or ideas that you may have regarding the slab-lifting method or any alternate methods you may know about.

— Ed Sanwell

ANSWER: I understand your concern with the components in the soil underneath your basement floor slab and I share your worries. While mudjacking can be an excellent solution to sinking concrete in several situations, your basement floor slab may be too risky for this approach.

Mudjacking is a process where a special mixture of very fluid expansive clay is physically pumped underneath an object to reposition it. Once the object is in the right location, the mixture is left to cure and it should maintain its position for many years after the repairs. This is most commonly used for solid exterior concrete slabs, like driveways and sidewalks, but can have other applications.

I have seen many of the telltale signs of mudjacking — small round concrete patches in the surface of such slabs — on many homes. Talking to homeowners who have had this service performed, the success rate is quite high and slabs often maintain their raised positions for a decade. But the process is not perfect and performance can be dependent on the soil conditions below and adjacent to the concrete slabs.

Several years ago, I had occasion to meet the owner of Muddruckers when he did a presentation to our CAHPI-MB inspectors at one of our regular meetings. At the time, he stated they could lift almost anything with their process, but stayed away from lifting entire buildings due to possible complications and liability. If they make a mistake on a driveway, they can just redo the work. But if they make a mistake lifting a garage or addition foundation, there could be major structural implications.

I have the same reservation about lifting your basement floor slab.

The problem with mudjacking is that it can be very difficult for the contractor to know if and where excess material being pumped under the slab is going. While this slurry will easily fill voids and allow upward pressure to be exerted to lift the concrete, preventing reoccurrence of the sinking, it may also go in areas that are not desired. I have seen this happen in crawl spaces adjacent to areas that have been raised, and it could happen under your basement floor.

While you may be correct that it will somewhat homogenize with the pea gravel under your floor, that should not create any serious issues. The real concern is lifting plumbing drains or weeping-tile piping to improper locations if there are now voids under these critical items. These plastic pipes may still remain close to their original location underneath the slab, even though the floor has dropped. If they are artificially raised with the mud slurry, they could lose their proper slope or even become damaged if they are stressed excessively. If the mudjacking compound is installed on top of these pipes, it could force them down into the voids below, causing damage by detaching them from the concrete floor or sump pit.

It’s possible the contractors have enough experience to avoid pumping their product in areas near drain pipes, at least until the floor is sufficiently raised. Then, the rest of the voids could be filled without as much concern. To accomplish this it may be necessary to locate and map out all the existing under-slab piping. This could be done with the aid of a snake video camera, often used by rooter technicians and plumbers to locate blockages in these pipes.

The next consideration is to determine the actual reasons for the dropping floor in the first place. Since your home is on piles, there should be little movement in the actual foundation walls or support columns. But that does not prevent soil from eroding under the floor slab and disappearing underneath the foundation walls.

If that is the true cause of the dropping floor, it may indeed be due to major erosion or changes in the riverbank. This will probably not improve over time, so fixing your floor now may not prevent a reoccurrence.

It may be more prudent to invest the money and effort into stabilization of the soil around your home or the riverbank, rather than worry about the sunken floor slab and cracks in the walls and ceilings.

Before tackling the floor-slab issue, I would consult a geotechnical engineer familiar with your area to inspect your property and do some soil analysis to see if something can be done about the underlying cause. It’s always prudent to attack the root cause of a major structural defect before attempting to repair the symptoms of that defect.

If you don’t find a way to fix the cause of the eroding soil, it will likely soon reoccur and you’ll be pumping money, with the mud, underneath your floor.

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

 

trainedeye@iname.com