Step 18 - The Garage Slab

Our structural engineer, Dave Groverman, recommended that we pour the garage slab sooner rather than later. The strength of the slab will help the retaining walls resist pressure from the earth on the outside. So Mark and his crew took a break from framing to work on the slab.


Miguel Gomez brought in 9 inches of gravel for the base. As before, Stego was placed on top of the gravel as a vapor barrier, to keep any ground moisture from getting into the structure. The edges of the Stego were overlapped and taped so there are no gaps. Rebar was laid out on dobies over the Stego and wired together. The concrete needs to be 5 inches on top of the base, and a line was snapped all along the retaining wall showing where the finished height of the slab needs to be. Although the line looks totally level, it actually has a slight slope toward the street for drainage purposes. On the front where the garage door will be there is obviously no wall to pour up against. Here Mark placed a form board. The top of this board is at exactly the same level as the line on the walls. The form board has to be very firmly secured so it doesn't blow out when the concrete is poured up against it. Tape was applied below the snap line creating a seal between the Stego and the wall. This is as moisture tight as you can get. The whole thing was inspected and we were given the okay to pour.


On pouring day we had the usual crew - concrete from Superior with pumping by Kennedy. Mark had ordered a stronger concrete mix for this slab (3,500 psi) because of the extra weight and side forces it will have to withstand. After the concrete was pumped in, two finishers went to work smoothing it. We did not have expansion joints put in by the finishers. Instead we decided to have them cut in the next day with a concrete saw. The end result is floor that is as smooth as your kitchen table.