pumice and concrete title pumice and concrete single column title

Lightweight Insulating Concrete

pumice aggregate (Hess Grade 3/4x5/16MN)

ABOVE: Standard pumice concrete aggregate (Hess Grade 3/4 x 5/16MN). BELOW: Standard pumice concrete sand (Hess Grade 1/8 Fines MN). The MN designation is for “mine grade.” Mine grades are ideal for concrete aggregate because they are 1) economical—minimally processed and sold in bulk (by the ton), and 2) naturally contain some moisture.

pumice sand (Hess Grade 1/8MN) placing pumice concrete with a pump and boom

Proportioning, mixing, and placing pumice concrete is similar to that of standard concrete, with a couple of key differences.

micrograph of a grain of pumice sand showing foamed-stone structure

This micrograph of a particle of pumice sand clearly shows the amorphous, foamed stone nature of pumice. It is this inherent structure—even in the pumice sand grains—that imparts the lightweight and insulative characteristics to pumice aggregate.

PUMICE CONCRETE[01] is composed of Portland cement, pumice rock, pumice sand, pumice pozzolan and water. Compared to standard concrete, pumice concrete offers roughly a one-third reduction in weight. Proportioning, mixing and placing are done in a similar manner to that of standard concrete. Pumice concrete is placed and finished with typical concrete equipment and tools and is used, with one exception, for the same applications as sand-and-gravel concrete. That exception: due to the nature of pumice aggregate and sand, pumice concrete takes much more effort and patience to work to a standard surface finish, and for that reason is rarely used for extensive flatwork. But for any and all applications where pumice concrete is vibrated into forms, it presents no placement challenges beyond standard concrete and actually presents several advantages.


Of significant note, lightweight pumice concrete can be handled in larger volumes by lighter-duty equipment with less wear and tear on that equipment, and there is a significant reduction of dead weight on supports and formwork. Additionally, the unique lightweight quality of pumice concrete contributes to a decrease in structural steel costs, equipment and form demands, and, consequently, job costs. Also, pumice concrete has superior resistance to harsh weather conditions like freezing and thawing and an R-value some 4-times that of ordinary sand and gravel concrete—making pumice concrete ideal for colder climates and locations that experience dramatic fluctuations in the weather and temperature.


Lightweight insulating concrete is also notable for dampening sound transmission, for elasticity that reduces brittleness under earthquake conditions, for not spalling under exposure to direct flame, and for mitigating or eliminating moisture condensation on walls and ceilings.

01—The term “pumice concrete” is not to be confused with “pumice-crete.” Pumice-Crete® is a brand-name building material using a specific formulation of pumice and portland cement for a specific proceess and cured product outcome.

Pumice Concrete in Insulated Concrete Forms

insulated concrete forms

Insulated Concrete Forms (ICFs) were developed to combine the enduring strength of concrete with EPS foam insulation for an expedited wall and decking system construction solution. ICFs provide the shaping, structural form for the concrete and then are left in place to provide remarkable insulation value. Pumice concrete provides an exceptional fit for ICF construction by:

1) Boosting the overall R-value of the wall or deck by adding its 4X R-value advantage over standard concrete to the building envelope.

2) Lightening the deadweight load of concrete on the ICF forms. This means less prep work is needed to prevent blow outs, brace walls, and support floor and ceiling decks.

Properties of Hess Pumice Aggregates

A look at the pumice aggregates properties per ASTM-standards testing (download below). Also tabled is grading data for the pumice aggregates (per ASTM C330) used in concrete.

Download a PDF with data on the Properties of Hess Pumice Aggregates.

Preparation, Mixing, and Placing Pumice Concrete

concrete trucks

The pumice aggregate should be uniformly prewet to reach total saturation, then allowed to sit until excess water drains out. This will fill the natural internal voids in the aggregate with water. Why? Prewetting will prevent drying out on the way to the placement site and slump will be uniform throughout the load as well as from load to load. Pumice concrete also pumps better when the aggregate and sand is prewet.

Download a PDF with Instructions for Mixing and Placing Pumice Concrete.

Pumice Concrete Mix Designs

The right concrete mix design is influenced by a host of job-specific variables. Hess Pumice does not have a concrete engineer on staff and does not provide custom mix designs, but we have assembled a handful of designs (linked below) that can serve as a reference and starting point.

Download a PDF with data on base Pumice Concrete Mix Designs.


—Download PDF: Instructions for Mixing and Placing Pumice Concrete.

—Download PDF: Pumice Concrete Mix Designs.

—Download PDF: Properties of Hess Pumice Aggregates.

—Download PDF: Pumice Aggregates for Internal Water Curing, a research paper from the National Institute of Standards and Technology (U.S. Department of Commerce).

—Website: Using foamed-stone aggregates for thermal resistant concrete.