I have a garage floor that when we purchased the house the garage wasn't in use. My question would be the floor has dropped about three to four inches, I built a ramp on the outside to drive into the garage also. A higher wheel base vehicle can be driven in, lower one cannot. Can I just resurface a new layer of concrete ontop of the old concrete or will I have to redue the floor, taking old off replace with new????
Yes, no, maybe. First, if this was new construction, and not too many years have elapsed, it may be covered by new home warranties that some states have. Before it can be determined how to solve it, you need to determine why it has sunk and if it will continue to sink. It sounds like it did not have a properly compacted base. I'd suggest getting an engineer's opinion.
If the concrete is still in one piece, I would break out a section in each corner and check under it. If there is no hollow space, and the fill is firm, and the concrete hasn't moved in the past year, you may be able to get a new slab poured over top and fill in the broken out corners.
If the concrete is broken up across the slab, the new one will crack on the same line. You may be better to replace it entirely. Be sure to get fibre concrete and add some steel rods in areas of stress whichever method you use.
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