More Boring Home Ownership Stuff: Mudjacking a Sinking Sidewalk, Patio, or Other Surface

A sinking sidewalk can be bad news for you and your guests. Where the pavement is uneven, someone's bound to trip eventually.  Uneven surfaces less than 1/2 inch are usually not a serious problem. Surfaces 1/2 inch to ¾” inch are questionable and should be addressed sooner rather than later. Surfaces over ¾” inch have a problem and should be address.  In the winter uneven surfaces are first to puddle and ice, someone may slip.
Surfaces that are flat or pitched towards the home should also be a concern.  Hard surfaces should be pitched away from the home, to prevent water from entering the basement.  Clean gutter, having adequate downspouts/extensions and sealing hard surfaces and the exterior wall  is an essential part to your maintenance plan.
Pavement sinks because exterior concrete is always on the move. Soil settles. Moisture moves soil up and down. In cold climates, frost can heave and lift concrete slabs.  
Tearing out, hauling away and replacing an entire sidewalk or driveway is expensive - and hard on the environment when all that concrete ends up in a landfill. But if your concrete is in good shape (large sturdy pieces and a surface that is smooth and solid), you can avoid this process.
If that's the case, a process called mudjacking can level the concrete slab. For about one-third the cost of replacement, a specialized contractor will drill holes in the slab and pump ground stone or a cement slurry under it. With just a little bit of pressure, the slab will be raised back into position. A few more holes are used to fill voids, and then a concrete mix is applied to patch the holes flush with the surface.  Some contractors are now offering a special type of spray foam. Make sure you ask your contractor for options.