Frequently Asked Questions

Expanded perlite is a versatile and technical material that serves a variety of industries and uses. Read on or consult our list of downloadable brochures to learn the answers to common questions about perlite and its many applications.

General FAQ

What is perlite?
Perlite is a naturally occurring siliceous rock that expands 4 to 20 times its original size when rapidly heated to approximately 1,700 °F. In reality, expanded perlite is a "popped rock" that is inert, lightweight, sterile, permanent, incombustible, asbestos-free, non-toxic, rot and vermin proof and has a neutral pH.
How does perlite expand?
Two types of water, H2O and OH (a negatively charged water of hydration) are contained and internally bound in perlite ore. When rapidly heated to an appropriate temperature, perlite's silicate structure softens and both types of water turn to steam, blowing or expanding the viscous mass into a glassy silicate bubble froth consisting of tiny closed air cells on the inside surrounded by an extremely large broken bubble surface structure. As an analogy, think of popping popcorn.
What are perlite's physical properties after expansion?
Perlite is a natural combination of mixed glassy silicates making it inert and resistant to chemical attack, except for hot concentrated alkali and hydrofluoric acid. It slows thermal conductance, is incombustible (melts above 2000°F) and has no buffering capability. Each perlite particle resembles a glassy froth of bubbles. The internal structure consists of numerous tiny closed air-filled cells. This structure imparts lightness, natural insulating properties and limited compressive strength. Liquids cannot penetrate the cells. Perlite's external surface is composed of broken bubbles surrounding the closed frothy cells and is open, extremely large and jagged. This irregular surface adsorbs or holds matter making it an ideal filtration media. In horticulture, perlite's surface helps keep planting media open and lightweight. It provides a pathway for air and moisture to access plant roots. It holds moisture and nutrients for assimilation by roots over time. Perlite's high capillary action benefits hydroponic growing and its sharpness can scarify pests as well as act as a polishing agent and scrubber in various products.
What elements are found in perlite?
Typical elemental analyses show that perlite contains silicon, aluminum, potassium, sodium combined with oxygen and other trace elements. Each perlite ore deposit has separate and distinct ratios of these mixed glassy silicate which explains why certain deposits are better for specific applications. See the brochure Perlite Physical Characteristics on our website for a Typical Elemental Analysis of perlite.
Does perlite come in different sizes and weights?
Perlite is available in its crude ore form and in expanded product grades. Densities range from as high as 80 lbs./cu. ft. for ore and as light as 3.0 lbs./cu. ft. when expanded. A specific application dictates which product grade is most compatible.
What perlite products does Supreme Perlite offer?
In certain cases, we can tailor products for your specific use. In general, we make products for horticulture, construction and industry. Horticultural perlite is sterile and has a neutral pH. When used in propagation and planting media, it insures excellent aeration and drainage. It also lightens media and increases total pore space for healthy root growth and development. Perlite keeps media open and friable so that plants can be transplanted with minimum root tear. Those pesky garden weeds can be easily pulled too!
Does perlite help fertilize plants?
No. Perlite is sterile with no nutrient release. However, perlite will retain moisture and nutrients on its surface area for use by the plant. Normal fertilization and watering routines must be used. Perlite offers no buffering or cation exchange.
How can I tell if my planting mix is amended with Perlite?
Give the "little white particle" the thumbnail test. There are three prevalent soil amendments in the northwest and they are all white or off-white. Push your thumbnail into the middle of a particle. If it springs back, it's polystyrene. If it's resistant to breakage, it's pumice. If you can put your nail through it with moderate resistance, it's perlite!
How does Perlite's light weight help?
Reduced media weights will lighten workers' loads when handling plants or media. Lighter planting media decreases worker injury potential. Also, reduced shipping weights result in more product shipped per truckload.

Industry-Specific FAQ

Can landscapers benefit from using perlite?
Absolutely! Perlite changes soil structure. Clay soils will drain better while sandy, droughty soils will retain more moisture. Perlite amended planting areas are easier to work with making weed-pulling a snap. Rooftop gardens, balcony planters and movable planters all can benefit from decreased weights. Fully watered soil weighs up to 125 lbs. per cu. ft. whereas a well wetted perlite/peat moss mix weighs as little as 40 lbs. per cu. ft.
Why is perlite used in construction?
Perlite is substituted for sand or heavier aggregates in concrete and plaster mixes to reduce weights and achieve better insulation and fire protection. Perlite is naturally incombustible, resistant to thermal transmission and lightweight. Using lighter perlite materials means that, in turn, structural building elements can be smaller, lighter and less expensive.
What construction applications utilize perlite?
Applications of lightweight perlite concrete and plaster include roof deck construction, non-load bearing curtain walls, floor fills, slabs on grade, floating floors, chimney-lining systems, underground pipe insulation, bricks, tiles, fire door cores, radiant floor heating, in-ground swimming pool base and loose fill insulation.
What about perlite's insulation uses?
Perlite's R-value is nearly 3.0 per inch at 6-lbs./cu. ft. density. It registers 0,0,0 on ASTM's E-84 fire tests for flame spread, fuel contribution and smoke density. Construction Grade perlite is poured directly from the bag into CMU block and cavity walls. UL Design U905 shows that a 2-hour fire rated 8", 10" or 12" concrete block wall improves to 4-hours when cells are filled with perlite insulation.
What industrial applications benefit from perlite?
Perlite is used as a filler, extender and texturizing agent in numerous products. It displaces expensive resins and reduces unit weights. Perlite's filler applications include caulks, textures, joint and taping compounds, paints, polishes, hand cleaners and explosives. Additional uses include filtration, waste water treatment, oil clean-up, sludge solidification, exothermic toppings, slag treatment, insulating refractories, low density well drilling mud, foundry core and molds, formed products, shipping dunnage and adsorbent.
What are future uses of perlite?
Future perlite uses will evolve out of a better understanding of its attributes, improved processing capabilities and knowledge of synergies realized when combined with other products. Some possibilities are:

Growing with much less water
Increased hydroponic growing
Methyl bromide replacement growing cultures
More rapid composting
Physical insecticide
Activated material carrier
Stronger aggregate for lighter but stronger concrete
Contact Supreme Perlite