DIY Sunken Floor

Wooden Floor

• 1

  Inspect the wood floor joists from the basement to identify the bowed or bent joist that causes the floor to sink at that point. Cut a sister joist identical in dimensions to the damaged joist using a handsaw.

• 2

  Measure and cut a 4-by-4 post long enough to span three joists. You will install this post perpendicularly under the three joists, keeping the bowed joist in the middle.

• 3

  Place a hydraulic jack under each corner of the post. Crank the jacks to raise the post until it is just below the joists. Slide the sister joist next to the damaged joist. Continue to raise the post until it falls flush against the lower side of the joists.

• 4

  Crack the hydraulic floor jacks no more than 1/8 inch every day to press the post against the joists, straightening the one that is bowed. This gradual increase prevents cracks in the drywall.

• 5

  Place a level on the surface of the wood floor to determine when it is level, so you know when to stop cranking the jacks. Spread construction adhesive over a side of the middle joist when it is straightened.

• 6

  Press the sister joist against the glued side to secure them together. Drive a series of 16d finish nails through the two joists, spaced 16 inches apart, until their heads are flush against the surrounding wood surface. Remove the jacks so the sister joist supports the middle joist.

Concrete Floor

• 7

  Bore a series of 12-inch-deep, 1-inch-wide holes through the sunken concrete slab using a rock hammer. Space the holes 3 to 9 feet apart, depending on the size of the slab, 1 inch from the edge.

• 8

  Mix fly ash, Portland cement and sand until it achieves a workable consistency. Add the grout into a concrete pump and extend its hose into one of the holes in the sunken concrete floor slab.

• 9

  Pump the grout into the hole, keeping the pressure between 50 and 100 pounds per square inch. The pressure gauge on the pump will indicate the current pressure. The grout raises the section of the concrete slab as it is poured into the hole.

• 10

  Insert the hose into another hole in the slab and continue to pump the mix into it. Check the top of the slab periodically to ensure it is level, so you know how much more concrete you need to add. Repeat this process until you pump grout into all the holes, thereby raising the slab to your desired level.