Most concrete trouble in San Jose starts in the ground. The valley's clay moves with moisture, big trees grow close to paving, and winter rain arrives in bursts. Here are the questions we hear most.
Do I need to worry about drainage?
Yes. Drainage is the first thing to plan. Water that soaks the clay under or beside a slab makes it swell, and water that ponds on top finds every crack. New concrete should fall away from buildings, commonly about a quarter inch per foot, toward the street, a drain or planting that can take it.
My patio slopes toward the house. How bad is that?
It is worth fixing. A patio or driveway that slopes toward the house sends rain to the foundation, and wet clay at a foundation moves the house as well as the slab. Options are a channel drain along the wall, replacing the slab with the correct fall, or lifting the low side if the slab is sound.
Can tree roots crack or lift concrete?
Yes. Tree roots lift concrete as they thicken. Street trees along San Jose's older blocks and yard trees planted beside a driveway are the usual sources. Roots follow moisture, and the underside of a slab is damp, so they run right beneath it.
Can I fix the concrete and keep the tree?
Often you can keep the tree. Choices include routing the new slab around the root zone, bridging over a root with a thinner base, using pavers or separate pads near the trunk, or pruning selected roots under an arborist's advice. Street trees are regulated by the City and need a permit for root work. Cutting major roots risks killing the tree or making it unstable.
My neighbor's new concrete sends runoff onto my property. What can I do?
Start by showing your neighbor where the runoff goes during rain, with photos. Many cases are solved with a small drain or a curb along the edge. If that fails, the city's code enforcement office can tell you whether a rule is being broken, and an attorney can explain your rights under California law. This is general information, not legal advice.
Does clay or soft soil change the job?
Yes, clay changes the base, the steel and the drainage. On adobe clay we remove the topsoil, compact the subgrade, add crushed rock, reinforce the slab and keep irrigation off its edges. Soft or filled ground, which turns up near creeks and in the low land toward the bay, may need deeper excavation or an engineer's advice.
Why does my slab move more in drought years?
Because the clay dries deeper. In a dry year the soil shrinks away from slab edges and foundations, and gaps open that you can put a hand into. When rain returns it swells back, not always evenly. Even, moderate moisture around the slab limits the swing.
I have a gravel driveway that turns to mud. Is concrete the fix?
Concrete fixes a gravel driveway that turns to mud, provided the mud is dealt with first. The soft material is dug out and replaced with compacted rock before the slab goes down. Semi-rural lots in Almaden, the east foothills and the south county are where we see this most.
My patio was poured over an uncompacted trench and it settled. Can it be fixed?
Yes. A strip that settles over a utility or drain trench is a classic fault. If the slab is intact, the void can be filled and the slab lifted. If it has cracked along the trench, that strip is cut out, the trench is compacted in layers and the strip is poured again.
I live in a flood-prone area. Should the patio or slab be raised?
In a flood zone, raising a building slab is a matter for the city and your plans. Parts of San Jose near Coyote Creek, the Guadalupe River and Alviso are in mapped flood zones with their own floor height rules. For a patio, the aim is that water drains off and away quickly and that the slab does not block the path floodwater takes across the lot.
Do sprinklers really damage concrete?
Indirectly, yes. Sprinklers that wet one edge of a slab every day keep that strip of clay swollen while the rest dries, and the slab tilts or cracks along the line between them. Drip irrigation and a gap between lawn and slab make a clear difference.
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