Q: I have a small garage 20'x16' that is built on concrete blocks...
...the center has to be lifted up to level it. What would be the best way to do this? the floor is plywood that has been screwed to the floor.The blocks form the entire floor with plywood on top. This garage mainly was used for storage. I believe blocks form the the exterior walls, with rows that are four feet apart through the inside of this building. I believe there are four rows of blocks that the plywood sits on.
A: If this floor is made 100% from concrete block (with the plywood on top)...
...I would strip off the plywood and level out that center depression with a small pour of concrete. Then, I would screed out the concrete flat. Then leave it all concrete, no plywood.But it sounds more like you've got "joists" built out of concrete blocks. I deduced that from your comment about rows every four feet (this also goes along with your 16' measurement). In this case, I could again strip off all the plywood and see what you've got underneath. Consult with a concrete guy to see if it is possible to fill in the areas between those "joists" with concrete on top of a rock bed.
If he says that it can't be done, then the final option is to run a chalk snap line from one end of the "joist" to the other end. That way, you can see exactly how low the center of these "joists" have sunk. Then, fill in the depressions with sleepers--your choice of filling materials (small pieces of plywood or spare composite roofing shingles are good options). Then nail plywood back down again--preferably new, thicker exterior-grade plywood.
