questions and answers about pumice



Why is pumice an excellent abrasive?


In short, a complimentary relationship of form factor and chemical composition. The pumice form factor is that of an amorphous foamed stone, which gives it friability, meaning it gives rather than gouges under pressure. The chemical composition makes pumice glass-like, which brings cutting edges and just-right hardness. Pumice also combines readily with various fluids to make abrasive compounds, which, along with pumice grade size selection, add even more control to cutting rates.

Another valuable combination that comes into play with the Hess pumice deposit in particular is a natural hardness and purity combined with additional process purification: Hess has an entire plant designed to remove the trace amounts (less than 2%) of heavier, harder igneous minerals that are in with the pumice.

Download Knowledge Brief: Pumice: A Full-Featured Abrasive for Circuit Board Preparation


Can pumice be used to improve poor or damaged native soils?


Pumice is especially effective in opening up tight, compaction- and run-off-prone clay soils. Several inches of pumice tilled to root depth reshapes the structure of the soil, creating tilth by infusing a vital matrix of air-exchanging pore spaces into the root zone while also improving infiltration, drainage, and moisture retention. Better yet, pumice does so economically, as it is naturally occurring and does not need to be puffed, or expanded, in a furnace to achieve its functional form.

Download Knowledge Brief: Conditioning Soil with Pumice

pumice used to improve soil profile for new lawn

Pumice (Hess Grade 1/8 Fines) was blended into heavy clay topsoil to improve tilth and the water-utilization profile of this newly seeded lawn.


What roles does pumice play in the construction industry?


Several. Pumice is arguably most famous as the lightweight aggregate in Concrete Masonry Units (CMUs)—so called cinder blocks. Pumice also finds utility as aggregate and sand in formed-and-poured lightweight concrete structures, precast concrete products (including pipe, tanks, tilt-up walls) and lightweight stuccos and bonding mortars. Pumice aggregate also fills a role as a lightweight geotechnical fill for infrastructure projects.

In fine-powdered form, pumice is a natural and highly effective concrete pozzolan, providing a host of benefits to standard (and problematic) Portland cement concretes. Also, pumice pozzolans combine with slaked lime to form Pozzolanic Hydraulic Lime (PHL) plasters and binders. Pumice is inter-ground with Portland cement to create ultrafine, ultra-enduring cementitious injection grouts.

Pumice also finds use as a soil amendment, improving the functional structure, drainage, and water-retention profile of poor native soils beneath landscaped cover plantings. Pumice is also a lightweight and functional component in functional urban landscaping: engineered green roof soils, ecology embankments, storm-surge bioswales (rain gardens), and filtration strips protecting waterways from runoff.

Microfine pumice powders are used as safe, functional fillers in paints and coatings, epoxies and caulks. Pumice grits are used to provide dimensional texture and holding grip to non-slip floor paints and plaster-holding primers.

See the Where can I find more detailed information on the various uses for pumice? question/answer below for links to sites with more information on the uses mentioned above.


Can the use of pumice in construction and landscaping processes contribute to LEEDS certification?


Indeed it can. Pumice finds a role in the U.S. Green Building Council’s Leadership in Energy and Environmental Design (LEED) certification program in the following areas: Brownfield Redevelopment and Remediation (rehabilitating damaged sites to reduce pressure on undeveloped lands). Rainwater Management and Storm Water Design: Quality and Quantity Control (replicate and limit disruption of natural water hydrology and water balance of the site). Heat Island Reduction (minimize impacts of microclimates and human and wildlife habitats). Outside Water Use Reduction and Water Efficient Landscaping (limiting or eliminating use of potable water resources for landscaping). Minimum Energy Performance and Optimized Energy Performance (incorporating thermal mass to reduce heating, cooling, ventilating and realize energy cost savings). Use of Regional Materials (use of local materials and reduced transportation distances). Reduce Cement Content (use of a supplementary cement material).

Download the white paper: Pumice and LEED Certification

logo for the USGBC

How does pumice improve concrete?


The improvement pumice imparts to standard concrete is directly related to the grade size used. When used as the aggregate component[1], pumice lightens the dead load weight, improves the R-value, sound dampening, freeze-thaw resistance, and fire resistance (against spalling). Pumice aggregate (rock and sand) grades directly replace common sand and rock and are mixed, handled, transported, and placed using the same equipment and methods.

When used in fine powder form as a percentage of cement replacement (functioning as a pozzolan[2]), pumice improves final cure strength, density, and freeze-thaw resistance, while mitigating sulfate attacks, alkali silica reaction (when reactive aggregate is present), and efflorescence. In short, pumice can greatly improve the longevity and functional life of the concrete structure.

1—Website: More information on pumice in concrete, including mixing instructions and some base mix designs.

Download Whitepapers: How Pumice Pozzolans Super-Charge Concrete Performance and Flatline Alkali-Silica Reaction for Pennies a Yard

concrete infrastructure failure

Natural pumice pozzolans not only replace a percentage of the cement in the mix design, they prevent this kind of premature structural concrete failure.


Is pumice absorbent?


It is, but not dramatically so. Pumice is both absorptive and hygroscopic (attracts/absorbs moisture from the air). Pumice holds moisture without swelling—without getting soggy. This makes pumice valuable as a soil amendment for poor draining and/or poor moisture-retentive soils. Pumice is also quite good at controlling oily or viscous liquid spills, as its foamed-stone nature pulls liquids in and it’s rough, riven surface grabs and holds the thick stuff.


Does pumice make a good filtration media?


The foamed-stone nature of even tiny pumice particles makes for an effective filtration media filtering culinary water, cleaning water for drip irrigation, produce washing and other processes. The rough and pitted surface area of a pumice particle provides aggressive filtration, being especially effective in capturing slippery organics. Pumice media back flushes readily: the lightweight particles are easily animated during the flush cycle. The range of pumice grade sizes available also allow the filtration media to be more effectively customized to the filtration task, load, and back flushing cycle frequency. Pumice can replace sand media or be used with sand in dual media setups. It can be used in tank systems, cartridge systems, and open bed systems.

Download Knowledge Brief: Pumice as Filtration Media.


Does pumice have application in engineered soils?


The effectiveness of pumice as a soil amendment also translates into engineering specialty soils for use in containerized growing, greenhouse beds, lightweight roof garden soils, and run-off filtration and stormwater surge-control soils around paved surfaces and in high-performance urban landscaping.

Order a Sample: Hess Grade 1/8 Fines (Soil Amendment)

roof gardens/green roofs

Pumice is a functional, enduring component in the lightweight soils engineered for roof gardens.


Are there really animals that bath in pumice dust?


Several critter types enjoy—and benefit from—taking dust baths. The most famous is the chinchilla, a dense-furred rodent of South American Andes mountain origin. Other rodentia-class animals also dust bathe. As do many species of poultry. The aggressively textured surface of pumice powder particles remove and capture gunk and grime between feathers and fur shafts. Pumice is also quite effective, especially in the case of poultry, at controlling the tiny parasites that afflict the birds, as the glass-edged, absorptive pumice particles act as a mechanical insecticide.

Website: ChillDust™ is formulated specifically for the dense fur of Chinchillas.


Does pumice work as a mechanical insecticide?


As of yet, pumice has not been studied extensively as a mechanical insecticide, but a comparison of pumice to diatomaceous earth, which does have well-documented application as non-toxic and effective mechanical insecticides, strongly suggests fine-powdered pumice grades would prove similarly effective against soft and hard-bodied insects. Pumice has both abrasive (sharp glassy edges) and desiccating (moisture wicking) properties: working together, both spell doom to insects that scurry through it.


Can pumice be used as a growing media in hydroponic and aquaponic systems?


Pumice is a clean, enduring soilless media for ‘ponics-style systems. It holds moisture, yet readily drains—and the drainage rate is easily controlled via grade selection (depending on crop type and need). Pumice does not swell or get soggy. Though lightweight, pumice from the Hess deposit is weighty enough to provide a steady base for root hold and top support. Pumice is tough: it resists break down, and in most cases (depending on crop), pumice can be cleaned and used again.

Website: Learn more pumice as a soilless grow media.

pumice grow media

Seedlings growing in pumice media used in a flood and drain aquaponics system


What types of personal care products use pumice?


Creams, soaps, gels, and tooth pastes and polishes. Pumice has efficient abrasive properties, and in fine-grit form, makes an excellent exfoliant. When added to cosmetic creams and exfoliating gels, frothy pumice grit stays in suspension and spreads evenly. When worked lightly across the skin, the microscopic edges cut loose, bind, and sweep away dead skin. Pumice adds grime cut-and-capture strength to heavy duty hand soaps and gels without the need for chemicals. Pumice powders combine beautifully with soaps and moisturizers. Grade choice and concentration dictate aggressiveness.

Download Knowledge Brief: Pumice in Cosmetics and Personal Care Products.

pumice used as an exfoliant grit

Pumice powders are used widely as the functional exfoliant agent in commercial products, but can also be added to a favorite liquid soap, gel, or moisturizer to create an exfoliant. (See Hess Pumice’s Magma brand.)


Is pumice good for scrubbing away hard water stains?


Yes. Pumice is used both in powder and manufactured-stone form as an abrasive to attack stubborn stains and hard water mineral build-up. Hess’ retail products division carries a pair of products to do the job: Pumouse™ scrubbing stones and Clean Cut™ pumice scrub powder. Pumice scrubs are only to be used on hard, non-porous surfaces, like fired ceramics and glass. Not for use on delicate surfaces like plastics, fiberglass, finished wood, marble, and painted surfaces.


Are there other pumice-like materials in the marketplace?


The utility and value of the foamed-stone form factor is evident by the number of pumice-like products being made and offered to market, with “made” being the operative word. Foamed mineral products (save a non-calcined form of diatomaceous earth) are all artificially expanded: puffed up by the use of a very hot kiln. These frothed products include all the expanded clays and shales, vermiculite, and recycled foamed glass products. The expansion process, of course, adds cost and torpedoes green credibility. Pumice is naturally foamed (calcined) by its explosive volcanic origin.

Website: A detailed look at pumice function and performance verses pumice-alike products in a variety of use categories—Pumice vs. X.


Can pumice be used as an economical replacement for expanded perlite to improve soil structure and function?


Yes, pumice can directly replace expanded perlite as a soil amendment/component. Research studies, like the one from the Department of Horticulture, University of Illinois[1], find pumice to be the physiochemical and in-soil function equivalent of expanded perlite. The downside of expanded perlite, of course, is the fiery energy it takes to expand it, which contributes significantly to its cost. For engineered soils at volume—green roof grow beds, commercial greenhouse production, palleted bags of retail potting soils—pumice is the economical choice. Same for large-scale projects faced with the need to amend poor native soils—landscaping, turf fields, construction site remediation, and engineered storm water control/filtration constructs. Economical because pumice is naturally calcined (expanded) and need only be minimally processed for use as a soil amendment. The soil-amending pumice grades are sold by the ton, grade-prepped, and truck-loaded directly at the mine. Process-wise, it doesn’t get more economical than that.

1Evaluation of Pumice as a Perlite Substitute for Container Soil Physical Amendment. Noland, Spomer, Williams; Dept. of Horticulture, University of Illinois.

close up of rough pumice surface close up of bubbly expanded perlite surface

Close-up images of pumice (left) and expanded perlite (right).


Where can I find more detailed information on all of the various uses for pumice?


Hess Pumice Products publishes extensive information on the various processes and end-use products that use pumice. A wide and detailed overview is found on the primary Hess Pumice website, including suggested grades for each use. White papers, knowledge briefs, research summaries, infographics and other informational publications are available (in PDF file format) from that site’s Downloads Library.

Additionally, Hess has websites built around specific pumice-use topics and branded products, including:

Pumice Pozzolan, including tightly focused sites on ASR Mitigation and Pumice as a Replacement for Fly Ash.

Pumice in Agriculture (crops, livestock care, waste management).

Micronized, Non-Crystalline (NCS) Functional Fillers.

Pumice as a Soilless Grow Media (hydroponics and aquaponics systems).

Pumice as a Soil Amendment (gardens, landscaping, and turf)

Pumice in Concrete (both as a lightweight aggregate and as a pozzolan).

Pumice Aggregate and Sand in Lightweight Stuccos and Bonding Mortars.

Pumice-Enhanced Ultrafine Cementitious Injection Grouts.

The Pumice Store features use and ideal grade information for several smaller-scale pumice applications: wood finishing, exfoliant grit, cleansing scrubs and stones, texturizing grits for paints and primers, soilless grow media for succulents and bonsai, compost amendment, blast mitigation, pet care, and more.