How To Mix Concrete for Curbing: Perfect Ratios & Pro Mixing Tips

The strength, durability, and workability of your landscape curbing depend almost entirely on one factor: the quality of your concrete mix. At Curb Depot, we emphasize that a professional-grade curb requires a professional-grade mix. Unlike standard concrete used for sidewalks or patios, curbing requires a zero- or low-slump mix to hold its shape immediately upon extrusion.

This guide provides the perfect ratios and essential pro tips we use every day to ensure our customers produce flawless, long-lasting curbing.

The Zero-Slump Difference

Standard concrete is wet and flows easily (high slump). Curbing concrete must be dry and stiff (zero-slump).

Why zero-slump? When the concrete is extruded from a curbing machine like our Harpten, it must be able to stand up on its own without slumping or collapsing. This stiff consistency is achieved by carefully controlling the water content. The mix should resemble damp potting soil—it should hold its shape when squeezed in your hand, but no water should drip out.

The Perfect Curbing Mix Ratios

While exact ratios may vary slightly by local aggregate, the following is the professional standard for a high-strength, durable curbing mix.

• Portland Cement (1 Part): The binder that provides ultimate strength to the curbing structure
• Sand/Fine Aggregate (2 to 2.5 Parts): Fills voids and provides workability for proper extrusion
• Water (Minimal): Activates the cement and controls slump for zero-slump mix consistency
• Admixtures (As Needed): Enhances workability, strength, and color for decorative applications

Note on Gravel: Unlike structural concrete, we typically do not use coarse aggregate (gravel) in our curbing mix. The small opening of the curbing machine’s mold and the need for a smooth finish require a mix composed primarily of cement and fine sand.

Pro Mixing Tips for Consistency and Strength

Achieving the perfect zero-slump mix is an art, and consistency is key. Here are our expert tips:

1. Invest in a Quality Mixer

Mixing by hand is inefficient and almost guarantees an inconsistent product. We strongly recommend using one of our dedicated concrete mixers. Our mixers are designed to handle the stiff, zero-slump mix required for curbing, ensuring every batch is homogenous.

2. Water is the Enemy

Add water slowly and sparingly. It is far easier to add a little more water than to take it away. A common mistake is adding too much water, which results in a weak, slumping curb that will not hold its shape and is prone to cracking.

3. Use Admixtures for Enhanced Performance

Admixtures are chemical additives that enhance the properties of concrete. We use them to:

• Improve Workability: Our Assurance Admixture acts as a plasticizer, making the stiff mix easier to extrude and finish without adding excess water.
• Increase Strength: Certain admixtures can increase the final compressive strength of the concrete.
• Reduce Cracking: Admixtures reduce shrinkage, minimizing the risk of hairline cracks.

4. Incorporate Color Correctly

If you’re using integral color, it must be mixed thoroughly to ensure a uniform color throughout the curb. The pigment should be added to the dry ingredients before the water. This ensures the pigment is evenly dispersed and doesn’t streak.

The Mixing Process

• Dry Mix: Add the sand and cement to the mixer. Run the mixer for a few minutes to ensure the dry components are fully blended.
• Add Admixtures: If you’re using powdered color or other dry admixtures, add them now and mix.
• Wet Mix: Slowly add the water, a little at a time. If you’re using liquid admixtures, add them to the water.
• Check Consistency: Stop the mixer and perform the “squeeze test.” The mix should hold its shape firmly. If it crumbles, add a tiny amount of water. If it oozes, you have added too much and must add more dry material (sand and cement) to stiffen the mix.

Mastering the mix is a critical step in the professional installation process. By adhering to these ratios and guidelines, you’re establishing the foundation for a durable, high-quality curb that reflects the professionalism of your business. For a complete overview of the installation process, check out our Landscape Curbing Process: From Planning to Installation in 7 Steps.

Start Mixing Like a Professional

Perfect concrete mixing separates amateur work from professional landscape curbing installations. These proven ratios and techniques ensure durable, high-quality results that build your reputation.

Ready to elevate your mixing capabilities? Contact Curb Depot today to discuss our professional mixers, specialized admixtures, and complete equipment solutions that deliver consistent, superior results on every curbing project you undertake.