How to Mould Cement Block

A Five-Step Guide for Consistent Production

Cement block moulding is the process of shaping a cement-sand-aggregate mixture into finished blocks using a precision mould under controlled vibration and pressure. UNIK has been manufacturing brick machines and molds since 2008, with over 15 years of export experience to 28 countries. This guide outlines the five essential steps for producing high-quality cement blocks.

1. Prepare the Mould and Machine

Before any cement enters the mould, the tooling must be ready.

Inspect the mould – Check the cavity for cracks, wear, or residual concrete from previous runs. Pay special attention to corners and core pin areas, as these are most prone to damage.

Clean thoroughly – Use compressed air and a soft brush to remove all debris. Never use metal tools inside the cavity; scratches will cause blocks to stick and reduce surface finish quality.

Apply release agent – Coat all cavity surfaces with a thin, uniform layer of mould release oil. This step is critical for clean ejection and extends mould life.

Mount the mould – Secure the mould to the block machine's vibration table. Tighten mounting bolts in a cross pattern to ensure even compression. Verify that the mould is level using a precision gauge.

Check machine settings – Confirm that vibration frequency, compression pressure, and cycle timing match the specifications for your block type.

UNIK moulds are manufactured from Cr12MoV or 9CrSi alloy tool steel with carburizing heat treatment, achieving surface hardness of HRC59-62 and dimensional tolerance of ±0.3mm.

2. Mix the Cement Properly

The quality of the finished block depends heavily on the mix design.

Standard cement block mix ratio – A typical ratio is one part cement, two parts sand, and four parts aggregate by volume. Adjust based on your specific strength requirements.

Water content – Add water gradually until the mix holds its shape when squeezed but leaves no wet residue on your hand. Target slump of 60-80mm for machine moulding.

Mix consistency – The mix should be damp enough to flow under vibration but dry enough to hold shape after ejection. Over-wet mix causes blocks to slump; over-dry mix creates voids and weak edges.

Mixing time – Blend for 3-5 minutes after all ingredients are added. Insufficient mixing leads to uneven strength; over-mixing can break down aggregate particles.

Testing – Before full production, run a small batch and test block strength after 7 and 28 days of curing. Adjust ratios as needed.

For interlocking or decorative blocks, UNIK recommends using smaller aggregate (≤10mm) and adding 5-8% more sand to improve flow into detailed cavity features.

3. Run the Moulding Cycle

The moulding cycle consists of four phases: filling, vibration, compression, and ejection.

Filling – Distribute the cement mix evenly across all cavities. Uneven filling produces blocks with inconsistent weight and density. For multi-cavity moulds, use a mechanical feeder for uniform distribution.

Vibration – Activate the vibration system. Typical frequency for cement blocks is 3,500-4,500 RPM. Vibration causes the mix to flow into all cavity areas, removes trapped air, and compacts the material. Insufficient vibration leaves voids; excessive vibration can segregate aggregates.

Compression – The press head applies downward pressure. Apply 15-20% higher pressure for dense structural blocks than for lightweight blocks. Hold pressure for 1-2 seconds to allow the mix to settle.

Ejection – The press head retracts, and the stripper pushes the formed blocks out of the cavity. Ejection should be smooth and even. Jerky ejection indicates rough cavity surfaces or insufficient draft angle.

Cycle time – Typical cycle time for cement blocks is 12-18 seconds, depending on block size and machine capability. Faster cycles increase output but may reduce block quality.

UNIK's UNT series machines feature Siemens PLC controls and Rexroth proportional hydraulics, ensuring consistent cycle parameters across thousands of repetitions.

4. Cure the Blocks Correctly

Freshly moulded cement blocks are weak and must be cured to gain strength.

Initial stacking – Transfer blocks to pallets or curing racks immediately after ejection. Handle carefully; green blocks can crack or deform under pressure.

Covering – Cover blocks with plastic sheeting or wet burlap for the first 24-48 hours to prevent moisture loss. Cement requires water for the hydration reaction that creates strength.

Curing period – Keep blocks moist for at least 7 days for standard strength, 14-28 days for high-strength applications. Spray water regularly if blocks are not in a sealed curing chamber.

Temperature – Ideal curing temperature is 20-30°C. Below 10°C, hydration slows significantly. Below 5°C, protect blocks from freezing, as ice formation destroys strength.

Curing methods – UNIK offers steam curing chambers and finger car systems that achieve full strength within 10 hours for high-volume production.

Properly cured blocks achieve 65-75% of final strength at 7 days and 95-100% at 28 days.

5. Inspect and Troubleshoot

Regular inspection ensures consistent quality and identifies problems early.

Visual inspection – Check every block for cracks, voids, uneven edges, or surface blemishes. Reject any block that does not meet your quality standard.

Dimensional check – Measure block length, width, height, and core positions. Use a template or calipers. Acceptable tolerance is typically ±1.5mm for standard blocks, ±1.0mm for interlocking blocks.

Strength test – Periodically crush sample blocks to verify compressive strength meets specifications. Standard hollow blocks typically require 5-10 MPa; solid load-bearing blocks may require 15-30 MPa.

Common problems and solutions:

UNIK moulds feature radiused corners (3-5mm) and Ra 1.6 surface finish as standard, eliminating two of the most common failure points.

Why UNIK for Cement Block Moulding

UNIK has been manufacturing brick machines and molds since 2008, with over 15 years of export experience to 28 countries. The company's moulds are compatible with more than 20 international block machine brands, including HESS, MASA, ZENITH, BESSER, TIGER, and Quadra.

Every UNIK mould is built from Cr12MoV or 9CrSi alloy tool steel with carburizing heat treatment, achieving surface hardness of HRC59-62 and dimensional tolerance of ±0.3mm. Expected lifespan is 80,000-100,000 cycles under normal conditions.

UNIK also offers complete block making machines, including the UNT series fully automatic servo block machines featuring Siemens PLC controls, Rexroth proportional hydraulics, and quick-change mould systems.

For more information or to request a quotation:

Website: www.unikmould.com
Email: sales@unikmould.com