Concrete Garage Slab Needs to be Replaced

I have leveled many houses in the houston area where we have a large subsidence problem. I see no problem with raising your garage and pouring a new slab. You might consider some kind of piers at about 6 foot on center. These should extend below the frost line. why can't you level the building, add new plates of pressure treated lumber under the existing walls and pour concrete and let the pressure treated lumber sink or sit in a 1/2" or more of concrete. I think you have many options before you demolish the structure. good luck john

Depending on the severity of the deterioration of the slab, if it can be salvaged by repairing it, that's your most economical solution. Simply remove the spalled areas to sound concrete, apply a 2-componant epoxy bonding compound to the areas to be filled and then pour fresh 3,000 psi concrete. Make sure the concrete is air-entrained to increase durability. If there are areas under the building, temporary support may be needed to replace those portions of the slab.

Your description of the concrete failures indicates that they are occuring only in certain locations (at this time). In otherwords, the failure is not widespread. Widespread failure would indicate conditions more serious than "old concrete". In my opinion, based on the height of the walls and the existing bracing , the walls should act as a beam of significant depth to bridge small locations where the foundation is temporarily removed. As a safety factor, you should temporarily attach a 2x12 to the 2x4 that bears on the floor slab. This temporary bracing should bridge a failed area (assuming the area to be replaced is relatively small). Then, you could remove the failed concrete and replace with new. Finally, remove the 2x12. Move on to the next area. I would caution you to only work on one area at a time. This method is probably a little more time consuming than jacking the building up, but much less expensive.