The garage is the one room in most homes that nobody decorates, so it is also the room where the concrete is in plain view. Owners tend to notice its cracks first, sometimes years before anything shows inside the house. This entry is about reading that floor calmly: what is normal for a garage slab, what deserves attention, and why a Del Mar address adds a few considerations of its own.
A floor with a different job
A garage slab is usually poured separately from the house floor and often sits a step lower. The California Residential Code sets it apart in a couple of ways. Section R317.1 asks that a garage floor be of noncombustible material and that the parking area slope so liquids move toward a drain or toward the main vehicle door. Chapter 5 sets a minimum thickness for concrete slab-on-ground floors, three and a half inches, and points to the foundation chapter where soils are expansive.
Two things follow from that. A gentle slope toward the door is intended, not a defect. And the slab is a relatively thin plate resting on whatever base was prepared beneath it. It carries vehicles, storage racks and sometimes a workshop, loads the house floor rarely sees.
Cracks that come with the territory
Concrete shrinks as it cures and dries. In a large, open slab, that shrinkage nearly always produces a few fine cracks. On a typical garage floor these share some features:
- they are thin, often less than the width of a credit card
- the two sides sit flush, with no step from one side to the other
- they run straight across the slab or radiate from a corner of a pad or post
- they show up early and change little over the years
Saw-cut control joints are meant to give those cracks a place to form. A crack that wanders near a joint, rather than in it, is still usually shrinkage.
Writing down the date, taking a photo with a coin or ruler for scale, and marking the ends of a crack with a pencil is a simple way to see whether it is changing. Most of the time, it isn’t.
Patterns that ask for a closer look
Some patterns are different in character:
- Vertical offset. One side of a crack sits higher than the other, enough to catch a fingernail or a broom.
- Widening. A crack that was hairline last year now admits a coin.
- A network of cracks with a low center or high center, suggesting the slab is dishing down or doming up.
- Separation at the house step. The garage slab pulls away from the stem wall or curb at the house door, or drops relative to it.
- Matching signs indoors. A door from the garage into the house that now binds, or cracks in the wall above it.
Any one of these is a reason to look further, especially in combination. They point to the ground or the base beneath the slab rather than ordinary drying.
Salt in the air, rust in the slab
In much of Del Mar the ocean is close. Caltrans’ corrosion guidelines treat structures within roughly 1,000 feet of the ocean as being in a marine atmosphere, where airborne salt accelerates corrosion of steel. A garage door that stays open on summer afternoons brings that air in, and cars bring it in on their undersides after a drive along the coast.
When reinforcing steel or wire mesh near the surface begins to rust, it expands. The signs are recognizable:
- rust-colored staining that bleeds through a crack
- small areas of concrete that pop off, exposing a dark bar or wire
- flaking or scaling around the edge of the slab or near the door
This is a different problem from settlement and calls for a different response. Our page on foundation crack repair touches on how cracks are sealed and when they need more than sealing.
Low ground near the lagoon
Some Del Mar properties, particularly on low ground near the river and lagoon, are in mapped flood areas. The City maintains a page on FEMA’s newer flood maps, and owners can check whether their parcel is affected. In those areas, the garage is often the lowest enclosed floor of the house.
That has structural consequences worth knowing. Water that ponds against the slab, enters at the door threshold, or rises through joints can soften the base beneath the concrete. After a storm, a garage floor in a flood-prone area deserves the same calm look as after an earthquake: note new cracks, check for movement at the house step, and look for sediment in joints.
When the garage becomes a room
Garages are frequently converted to living space or accessory units. A slab that served a car may not meet the expectations for a habitable floor. Questions that come up include moisture beneath the slab, the step between garage and house, insulation, and whether the existing slab and footings suit the new use. Conversions go through the City’s Building Services and, depending on the property, other review. It is wise to understand the slab’s condition before plans are drawn.
Photographs between visits
Many homes here are occupied part of the year. A small routine, carried out on arrival or departure, keeps a useful history:
- Photograph the garage floor from the same two or three spots each visit.
- Note any new staining, flaking or cracks.
- Check that the door from the garage into the house closes and latches easily.
- Look at the floor after rain for ponding or water at the threshold.
A caretaker can follow the same steps. Over time, a few photographs answer the question of change better than any single visit.
Options when repair is warranted
Repairs follow the cause. Shrinkage cracks may need nothing at all, or a sealant to keep out water and grit. Corrosion damage calls for removing unsound concrete, treating or replacing the steel and patching. A slab that has settled or heaved may be lifted, partly replaced, or replaced entirely with a better-prepared base. Where the house foundation itself has moved, slab foundation repair addresses the larger structure first. We coordinate with licensed engineers as needed where design is required.
The factors that shape scope and cost include the size of the slab, the cause and extent of damage, access, whether the garage must stay usable, drainage corrections, corrosion repair, and any permits or plans required.
How we help
We look at the garage floor as part of the whole house, not in isolation. If you’ve noticed a crack that has changed, staining that suggests corrosion, or movement at the step into the house, we can document what is there and explain what it likely means. We serve all of Del Mar. Begin with a Free Quote.