Concrete mixer

What is a concrete mixer?

A concrete mixer combines cement, sand, gravel (aggregate), and water into fresh concrete with a uniform texture. Instead of hand-mixing in a wheelbarrow with a shovel, a mixer uses a rotating drum or paddles to fold the materials together. This produces consistent results, saves time, and helps you place concrete before it begins to set.

Most DIY-friendly mixers are portable, electrically powered drums with internal fins that lift and tumble the mix as the drum turns. Larger models may be gas powered and towable. For very large jobs, concrete is delivered by a ready-mix truck, which is also a type of mixer.

How a concrete mixer works

• Drum action: Inside the drum, fins or blades scoop and drop the material as the drum rotates, blending the dry components with water.
• Batch volume: Mixers are rated by drum volume, but the practical batch size is usually about one-half to two-thirds of that number. Overfilling reduces mixing efficiency and can strain the motor.
• Timing: Mix for a few minutes after all material is added. Too little mixing leaves dry pockets; too much can add air and cause segregation.

Common DIY uses

• Setting fence and mailbox posts
• Pouring small slabs and pads for sheds, AC units, and hot tubs
• Sidewalk and walkway sections
• Footings for decks and retaining walls
• Steps, stoops, and landings
• Concrete countertops and GFRC projects (with appropriate mixers)

Types and variations

• Bucket or paddle mixer: A drill-driven paddle used in a bucket. Best for small batches, thin overlays, or specialty mixes. Not ideal for gravel-rich concrete unless rated for it.
• Portable electric drum mixer: The go-to for homeowners. Usually 2 to 5 cubic feet drum volume. Plugs into a standard outlet and is easy to move around a yard or garage.
• Gas-powered towable mixer: Larger capacity and more power for frequent or remote work where electricity is limited. Heavier and louder, often rented for weekend projects.
• Mortar mixer (paddle-style trough): Uses internal paddles in a horizontal tub. Designed for mortar or stucco (sand and cement only). It can be damaged by coarse aggregate and is not intended for standard concrete.
• Truck-mounted mixer: Delivers large volumes from a batch plant. Best for driveways, foundations, and big slabs.

Choosing the right mixer

• Project size: Estimate your total volume. Volume (cubic feet) = length × width × thickness. One cubic yard equals 27 cubic feet.
  • 80-lb bag of concrete yields about 0.60 cu ft
  • 60-lb bag yields about 0.45 cu ft
  • 40-lb bag yields about 0.30 cu ft
• Capacity: Look at the mixer’s workable batch size, not just drum volume. If a drum is 4 cu ft, assume about 2–2.5 cu ft per batch.
• Power source: Electric is quiet and clean; gas offers mobility where outlets are scarce.
• Portability: Consider weight, wheels, and whether it fits through doorways or up ramps.
• Durability: Steel drums are sturdy; polyethylene drums resist rust and are easier to clean. Check bearings, frame stiffness, and motor quality.
• Buy vs. rent: If you only need it for a day or two, renting a larger mixer can be faster and cheaper than buying a small one.

How to use a concrete mixer

1. Prep the site: Have forms, reinforcement, and tools ready. Concrete begins to set quickly; everything should be staged.
2. Power and safety: Use a GFCI-protected circuit for electric models. Wear gloves, eye protection, long sleeves, and a dust mask while handling cement.
3. Pre-wet the drum: Add a small splash of water to reduce sticking.
4. Add materials: Start the drum. Add about two-thirds of the water you expect to use. Then add gravel and sand, followed by cement, and the rest of the water slowly. If using bagged concrete, follow the bag’s instructions and start with less water than the maximum.
5. Mix to consistency: Aim for a texture like thick oatmeal that holds shape but is workable. Avoid soupy mixes. Adjust water gradually.
6. Discharge: Tilt the drum to pour into a wheelbarrow, bucket, or directly into forms. Keep the mixer turning slowly to prevent setting inside the drum.
7. Repeat promptly: Plan your batches so you can place and finish the concrete while previous batches are still workable.

Maintenance and cleanup

• Clean immediately: Rinse the drum and paddles while the concrete is still wet. Add water and a few handfuls of gravel; let it churn for a couple of minutes to scrub the interior, then dump and rinse.
• Remove film: If residue remains, a plastic or wooden scraper can help. Avoid aggressive hammering that can dent or crack the drum.
• Lubricate and inspect: Check belts, guards, fasteners, and bearings. Tighten loose hardware and lubricate per the manufacturer’s schedule.
• Storage: Keep the mixer dry, covered, and off bare soil to limit rust and corrosion. Coil cords neatly and protect plugs.

Common mistakes to avoid

• Adding too much water: Weakens the concrete, increases shrinkage, and leads to dusty or weak surfaces. Add water slowly and stop when you reach workable slump.
• Overfilling the drum: Reduces mixing quality and stresses the motor or engine.
• Using the wrong mixer: Mortar mixers are not suited for gravel-heavy concrete; drum mixers struggle with very stiff or specialty mixes.
• Poor timing: Waiting too long between batches can cause cold joints where new concrete doesn’t bond well to older material.
• Skipping cleanup: Dried concrete in the drum reduces capacity and can be difficult to remove.
• Ignoring power safety: Running without GFCI protection or damaged cords increases shock risk.

Related terms

• Cement vs. concrete: Cement is the binder; concrete is the mixture of cement, sand, gravel, and water.
• Mortar: Cement, sand, and water (no gravel), used for brick and block.
• Slump: A measure of concrete’s workability or wetness.
• Aggregate: Sand and gravel or crushed stone in the mix.
• Screed: To level freshly placed concrete with a straight board or vibrating tool.

Practical examples

• Fence posts: For several posts, a small electric drum mixer lets you mix consistent batches and move quickly. Many DIYers use fast-setting concrete in post holes; still, measure water carefully and mix thoroughly for stronger results.
• Sidewalk section: A 10 ft × 4 ft slab at 4 in thick needs about 13.3 cu ft of concrete. That’s roughly 30 bags of 40 lb, 30 bags is a lot by hand, but a 4 cu ft mixer (2–2.5 cu ft workable batch) can handle it in 6–7 batches.
• Shed pad: For a 8 ft × 10 ft pad at 4 in thick (26.7 cu ft), consider renting a towable mixer or ordering ready-mix if access allows. If mixing yourself, plan helpers for a steady workflow.

A concrete mixer helps you produce consistent concrete faster, giving you more control over timing and quality. With the right size and good technique, it turns hard, messy work into a smooth, manageable process.