Volcanic or cement block? Compare the numbers, not impressions

Weight: up to a third lighter

At the same 20 cm thickness, a solid cement block weighs 33 kg and a hollow concrete block 18 kg, while a three-core volcanic block weighs 12 – 14 kg, dropping to 9 kg for the insulated volcanic sandwich type.

This difference affects three things every contractor knows: dead load on the slab, the number of blocks per truckload, and how fast a mason works in a day.

Thermal insulation: 0.125 W/m·K

Volcanic pozzolan has a thermal conductivity of 0.125 W per meter-kelvin — a low value that reduces heat transfer from outside the building to inside, and vice versa, by up to 98% according to the factory’s specifications.

Insulated block — cement or volcanic — relies on a polystyrene slab placed inside the block during the same production stage, not glued on after manufacturing. Municipalities and the electricity company require this technique for exterior walls.

Sound insulation: a 3 – 6 dB reduction

The voids in volcanic block help absorb sound waves and reduce echo, lowering noise by 3 – 6 dB. This is a key consideration in hotels and adjoining residential buildings.

Fire resistance: from 1.25 to 4 hours

Ratings issued for specific samples using the NCMA TEK method, based on equivalent thickness: insulated volcanic block with a center slab, 4 hours; American-style insulated volcanic, 3.5 hours; standard volcanic, 2.3 hours; and four-core hollow block, 1.25 hours.

When to choose which?

• Load-bearing walls and foundations: solid cement block with 14 – 18 MPa compressive strength, compliant with ASTM C90.
• Exterior walls in air-conditioned buildings: insulated block with a polystyrene slab.
• Interior walls and partitions: hollow block, 8 – 14 MPa, compliant with ASTM C129.
• Projects that specify a fire resistance duration: insulated volcanic block matched to the required duration.

In every case, ask for a recent lab report for the size you will supply — not for the whole product family.