Condo Floor Stabilization


Filling voids below the floor of a condo during construction, using foam jacking for condo floor stabilization.

Filing voids below floor.

A builder converting an old warehouse to condos discovered extensive voids below the slab floors, requiring condo floor stabilization.  The voids were discovered when installing new sanitary sewer lines.  A large box culvert runs under the building, and was thought to be the cause, along with backfill settlement.  

Inspection of the box culvert didn’t show any leaks which could cause erosion.  Because there were no leaks, backfill settlement was identified as the cause of the voids.  The floor slab had not settled.

The customer’s structural engineer would not sign off on the project unless the voids were filled.


High density polyurethane foam jacking to fill the voids below the floor as part of the condo floor stabilization. 

Because the floor had not settled, an undersealing foam had to be used.  Undersealing foams are specifically formulated for completely filling voids without lifting what they’re filling under.  

Many companies that do foam jacking don’t have access to undersealing (void filling) foams.  To get around this, they try to use lifting foams for undersealing.  This is not a good idea; it either results in not completely filling the voids, or lifting the floor.

Foam jacking for condo floor stabilization of condo under construction by filling voids below the floor using foam.

Condo slab foundation repair using foam jacking.


A Concrete Jack foam jacking crew undersealed the entire area in a few hours.  During undersealing, the box culvert below the building was checked to make sure leaks didn’t show.  The foam used on this slab foundation repair project cures in a few seconds, so the customer was able to continue using the area as usual. 

The void filling foam used by Concrete Jack on this project has more than a 7 time safety factor based on loads specified by the International Code Commission for dead & live load.  Despite being very lightweight, the polyurethane used by Concrete Jack for foam jacking is much stronger than the weight that the structure will apply to it.