Why a slab is a walking surface
A slab on an accessible route is a walking surface before it is a slab. The 2010 ADA Standards require ground and floor surfaces on that route to be stable, firm and slip resistant, and Chapter 11B holds the running slope to 1:20 and the cross slope to 1:48. A patio, a walk to a leasing office or a pad at a side door all fall under that once someone crosses them to reach the building, so the pour is set out from the levels rather than from the forms.
What cracks a slab is usually underneath it. Fill that was never compacted, a trench backfilled across the pour, a leaking irrigation line or a soil that swells and shrinks with the season all move the ground under the concrete, and the slab follows. Where a city's own records describe its soils, the city page states what they say. The answer here is the base, the thickness and the joints, not the surface.
Joints are where a slab is designed to crack. Concrete shrinks as it cures and a plain slab will crack somewhere, so control joints are cut to put the crack where it can be seen and sealed instead of running across a doorway or a patio. Spacing follows the thickness and the shape of the panel, isolation joints go in wherever the slab meets a column, a wall or a footing, and an edge beside a walk is formed so a later difference in level stays inside a quarter inch.
The weather at the pour stays in the slab. Heat, low humidity and wind together cost slump, speed the set and bring plastic shrinkage and thermal cracking, and water added on site to recover workability costs strength. Below 40 degrees, or with such a night expected in the protection period, the pour is protected instead. Concrete is held to 95 degrees at discharge.
What concrete slabs and patios includes
The area is walked with the manager or the owner and the levels are taken across it: where water has to run, where the slab meets a walk, a threshold or an existing pad, and what the finished surface has to match at every edge. Anything on an accessible route is recorded against its 11B value.
The old slab is saw cut to a straight line and broken out full depth. Saws run on a continuous water feed and grinders on dust collection under Title 8 section 1532.3, and the broken concrete leaves the site.
The subgrade is cut or filled to level, soft spots are dug out, and base is placed and compacted in lifts so the slab is carried evenly across its whole area.
Forms are set to the finished levels and the slopes are checked before anything is poured. Reinforcement goes in, isolation joints at columns, walls and footings, and the control joint layout is marked.
Concrete is placed, screeded and floated, then broom finished across the direction of travel so the surface is slip resistant when wet.
Joints are cut while the concrete is green, the slab cured and protected for the weather, and the finished slopes measured and photographed against what they had to meet.
A slab is judged by what happens after it dries. Where the crack goes, whether water runs off it, and whether a walking surface still reads 1:48 across when the tape comes out a year later.
Where new slabs are poured
Warehouse and dock pads
Exterior pads, apron slabs and equipment bases outside tilt-up buildings, poured thicker and jointed for the wheel loads that cross them every working day.
Retail and restaurant patios
Dining patios, enclosure pads and side-door landings, where the slope has to shed water away from the door without breaking the route into the suite.
Office and medical entrances
Entry landings, walkway slabs and generator or chiller pads, set flush with thresholds so nothing at the door becomes a change in level.
Apartment and HOA common areas
Mail kiosk pads, pool decks, laundry and refuse slabs and the walks between them, the surfaces residents cross most often and notice first.
Agricultural shops and yards
Equipment slabs, wash pads and shop floors at the edge of the fields, built for point loads and for what is driven across them.
Homes and rear yards
Rear patios, side walks, shed and spa pads and porch landings, poured to drain away from the house rather than back towards it.
Questions about concrete slabs and patios
Concrete shrinks as it cures, so a plain slab will crack somewhere. Control joints are cut early to put the crack in a line that can be seen and sealed rather than wandering across a patio. A crack that steps up at one side or keeps moving is a different problem, and that one is about the ground underneath.
Where people walk to reach a building, the surface is held to a running slope of 1:20 and a cross slope of 1:48, and it has to be stable, firm and slip resistant. Away from that route the slope is set to drain, usually away from the building. Either way the levels are measured, not judged by eye.
Sometimes, where the old slab is sound and the extra thickness does not raise the surface past a threshold or into a change in level at a walk. Where the old slab has moved, the reason is underneath it, and pouring over it buries the problem rather than fixing it.
It keeps the slab separate from anything that does not move with it: a column, a wall, a footing or a foundation. Without one, the slab drags on that fixed point as it shrinks or the ground moves, and it cracks from there.
Foot traffic and vehicle traffic come back at different points, and both depend on the mix, the thickness and the weather during curing. The estimate sets it out for the pour being made, rather than a general figure.
Concrete slabs and patios by city
Slab and patio work is requested through the concrete flatwork page for your city, which covers the stock and the permit route there.
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