Slabs & Foundations

Planning a steel shop or barndominium shell? CJM Metals can review the building layout with us so the footprint, foundation and anchor layout are coordinated before the pour.

Most of our slab work is a pad for something that arrives afterward: a metal shop or storage building, a prefab shed, a detached garage or workshop, a carport, a hot tub, a generator or an AC condenser. We work from the building's footprint and anchor layout, so the slab matches the structure instead of the structure being shimmed to fit the slab.

Carport pads are a family job: we pour the slab and set the anchor bolts to the post layout, and CJM Metals builds the steel carport on top of it. Equipment pads are small but not casual — an AC pad that tilts toward the house sends condensate at the foundation — so we compact the base and pitch every pad away from the structure.

Four inches carries foot traffic and a lawn mower. A shop floor that will see a vehicle, a lift or a loaded trailer should be 5 to 6 inches, with a thickened footing under any heavy point load. If a building supplier or engineer gives us a spec, we pour to the spec.

Reinforcement is a rebar grid, typically #3 or #4 bar at 16 to 24 inches on center both ways, tied and held on chairs so it sits in the middle of the slab instead of on the dirt. For a building we pour a monolithic turn-down slab: the edge thickens to 12 inches or more with two runs of bar, poured in one piece with the floor, so the footing has no cold joint for water to find.

The ground under a slab in Arlington is clay that swells when wet and shrinks when dry, so we strip topsoil and organics, grade to a consistent depth and compact a layer of crushed base, usually 4 inches. Pouring directly onto raked dirt is the fastest way to a cracked floor.

Under an enclosed building we lay a polyethylene vapor barrier over the base before the steel goes in; without it, ground moisture migrates up through the slab and shows up as sweating floors, rusted tools and peeling paint. Open carports and outdoor equipment pads do not need one. Finished slab elevation sits above the surrounding grade, and where a slab meets an existing driveway or the house we set an expansion joint.

Anchor bolts, straps or post bases go in wet, set to the building's bolt pattern and held to line while the concrete takes its set. Send us the anchor drawing and we set to it: cast-in bolts are stronger than drilled-in anchors and save the installer a day.

Control joints get cut within the first day at roughly 2 to 2.5 times the slab thickness in feet, so every 8 to 10 feet at 4 inches and every 12 to 15 at 6. Plan the build schedule around the cure: cars off for 7 days on a 4 or 5-inch slab and 10 days at 6 inches, heavy equipment and loaded trailers 14 to 28 days. Details are on the curing time FAQ.

The City of Arlington's DIY permit guide says a storage shed over 100 square feet requires a permit, so only the smallest sheds are exempt. A shop or a detached garage needs a building permit before work starts, carports and patio covers have their own rules, and setbacks, easements and HOA rules apply either way. Confirm what your lot allows with the One Start Development Center, 101 W. Abram St, 817-459-6502.

On expansive clay the City may ask for a sealed foundation design from an engineer on a larger garage or workshop. Many metal-building suppliers ship engineered drawings with the kit and we pour to those; if yours does not, we will tell you up front and can point you to an engineer. We put in writing who is pulling the permit — see the concrete permit process — and confirm the path before you order the building.