questions and answers about pumice



Where does the Hess pumice come from?


Hess mines pumice from a large deposit located in southeast Idaho, USA. The pumice came from a volcano on the shores of an ancient inland sea that, at one time, covered parts of the states of Utah, Nevada, and Idaho. Utah’s Great Salt Lake is the remnant of this prehistoric body of water. The exceptional purity of the Hess deposit is thought to be the result of centuries of wave action from that vast ancient sea that cleansed the heavy metals and other impurities before packing the white pumice tightly against the northern shore (present day southeast Idaho).

All pumice products distributed by Hess Pumice Products, Inc. and listed with the INCI as “pumice” are mined, processed, and packaged in the State of Idaho, United States of America. Products are exported under HS Tariff Code: 2513.10.0010.

hess pumice mine satellite image

A satellite image of the Hess pumice mine (center) in SE Idaho, once tucked into a water-filled finger canyon on the north end of an ancient inland sea.


Who is Hess Pumice?


Hess Pumice Products is a family-owned company that has been mining and refining pumice products for over 60 years. Blessed with an exceptional pumice deposit, the Hess family has worked relentlessly to develop refinement processes, grading and grade-blending processes, and logistical expertise to get their pumice efficiently to market. They also continuously pursue new industrial processes, commercial applications, and end uses for their pure white pumice.

Website: Read the Hess Pumice Story for a richer account of company history. Includes an insightful video presentation.


What is the pumice from the Hess deposit most known for?


Hess’ pumice fame and world-wide demand was ignited by combination of two characteristics: 1—pumice from the Hess deposit delivered superior abrasive performance, with reported abrasive benefits of 25 to 50% over other commercially-available pumice worldwide. 2—The pumice deposit is naturally clean, and with Hess’s ability to remove the trace amounts of non-pumice minerals, the purity is exceptional. That said, Hess has never stopped innovating and opening new markets for pumice. Today, Hess sells pumice for use in a wide variety of industrial processes and products.


What steps are needed to prepare pumice for market?


Preparing pumice for market is a straightforward and sustainable[1] process. Pumice is surface mined, then crushed and screened into several “mine” grades. These mine grades are sold by the ton and loaded directly for truck shipping from the mine. Select mine grades are hauled a short distance to the Hess Pumice industrial complex for additional processing and grade refinement. There, a pair of highly-specialized processing plants dry, crush, separate, grade, grade-blend, test (for specification consistency), and package some 70 different pumice grade products for shipment. These are the “processed” pumice grades. Packaging consists of small containers (as needed by customers) production bags (easy to palletize and handle at 35 to 50 lbs. per bag, depending on grade), super sacks, or bulk loads onto trailers or rail cars, including bulk pneumatic vessels for the fine powder grades.

1—See: Is pumice a sustainable resource? immediately below.


Is pumice a sustainable resource?


Pumice is indeed a sustainable resource: simple to mine, plentiful, and requiring minimal processing to reach usable grades-form. The refined-grade production process requires low-temperature drying, a trip through a crushing mill, particle screening and separating to size, and final packaging. The plant refinement processes generate no air-fouling emissions and no chemical waste (as chemicals are not necessary for the refinement processes).


What are differences between pumice “mine” grades and pumice “processed” grades?


Primary differences between pumice mine grades and processed grades: moisture content, number of grade sizes, and presence of adhered fines. The Hess mine grades are minimally processed, meaning they are crushed and grade-screened, but not dried or otherwise processed as required my more demanding particle-size specification applications. All mine grades, even those top-screened to remove fines, will contain some moisture-adhered fines (see image comparison below).

The plant-processed grades are refined in one of the two Hess processing plants. This refining process allows Hess to produce a wide selection of grades and specialized grade-blends. The refining process also facilitates: 1) the testing necessary to ensure each grade stays consistently on spec, and 2) various packaging operations.

Also see cost factors question immediately below.

pumice mine grade pumice processed grade

The image on the lefttop is the mine-grade version of Hess Grade 3/4 x 5/16. The image on the rightbottom is the processed grade equivalent. Note the presence of clinging fines on the mine grade stones.


What factors drive the cost of preparing pumice for market?


The minimally-processed mine grades have the fewest cost points. The more thoroughly refined “processed” grades necessitate drying, further crushing and screening to reach grade-specified particle size range, non-pumice mineral removal[1] (select grades), and packaging. Each of these processes, determined by the final grade specification, affect the cost of the final product.

1—The Hess pumice deposit averages about 2% igneous non-pumice minerals (such as obsidian), which are removed as part of the processing for select grades, which are used in specialized industrial processes.


What is the smallest pumice grade available?


Hess refines several ultrafine (micronized) pumice grades. The smallest (Hess NCS-3) has an average particle size of 3 microns. This smoke-like grade is used by industry as a highly effective concrete pozzolan (Brand name: Hess UltraPozz) and as a safe, functional non-crystalline silica filler for paints, coatings, epoxies, and caulks.

More information on Hess pozzolans is found on the website.


Where can one find a list of all pumice grades and grade blends offered by Hess Pumice?


A complete list of the Hess Pumice processed and mine grades is found on the pumice grades and types page. Technical Data Sheets (TDS) for each of the grades are linked there as well.


Where does one find help to determine if pumice would work for a particular process or product?


The Hess Research and Development VP has many years of experience working with a variety of process and product engineers to determine fit and function, processes, and grade. If needed, we can also work up a custom grade blend to meet the need.

Contact R&D at or call 208.766.4777 x 111


Where can one buy small amounts of pumice in various grades?


Hess has an online Pumice Store backed by a dedicated fulfillment center to fill small-quantity pumice orders. Pumice can be purchased in one-pound quantities up to full-sized production bags in a wide spectrum of grade sizes. The Pumice Store also sells a variety of branded direct-to-consumer products—chinchilla bathing dust (ChillDust™), SoilRox™ soil amendment, Magma™ exfoliating powders, Sedoso™ wood finishing rubs, Rūtsu™ bonsai growing media, and CleanCut™ scrubbing powders, to name several.

hess pumice store logo and link

What is the turn-around time when placing large-quantity pumice orders with Hess?


Plan on two weeks between placing a large order (full pallets and bulk-shipped quantities) and shipment. Hess produces some seventy grades and grade-blend products, and while we warehouse a limited stock of popular grades to fill small orders and service steady, low-volume customers, a two-week turn is typical to produce most orders.


Does Hess Pumice ship pumice products outside of the U.S.?


Yes. The Hess Pumice company has considerable logistical expertise, earned from decades of shipping pumice products around the world. We manage the complexities of domestic shipping for many of our customers as well—determining the most economical and efficient means, carriers, ideal load sizes, documentation, and needed permits.