Frequently Asked Questions

Company and Product Background Information

SPI has invested well over $2 million in independent laboratory testing ranging from accelerated aging all the way through various types of structural, fire, blast loading, and air/water infiltration testing to be certain that the system will perform under all conditions and in all climates.

Stone Panels International LLC is the only lightweight stone supplier accepted (approved) by the International Code Council (ICC), the building authority who writes and administers the model code for all construction in the U.S. and many other countries. The ICC-Evaluation Service has accelerated aging, structural and impact, fire, plus air and water infiltration requirements which must be met for products and systems to gain acceptance.

Stone Panels International LLC is the only U.S. manufacturer of lightweight natural stone composite panels accepted (approved) by the Miami-Dade County Building Code Compliance Office. That organization is responsible for evaluating exterior wall systems and testing for proof of ability to resist hurricane wind and large missile impact.

Ongoing quality control procedures are monitored by the ICC, the Miami-Dade NOA Compliance office, the British Board of Agrèment in the UK, and the Avis Technique in France.  Stone Panels International LLC is the only U.S. building products manufacturer accepted by the Avis Technique. This testing, quality control, and building official acceptance assures the design-build community that they are buying a system that will perform for many years.

StoneLite® panels use about 1/3 the amount of stone that is required for traditional stone cladding. Quarrying and transportation of dimensional stone requires a great deal of energy so the ability to harvest significantly less stone not only saves energy but also leaves more natural resources intact for future use.

At only 3.5 lbs. per sq.ft. and an allowable deflection of more than L/120, StoneLite® panels require less structural steel and concrete back-up as it can be installed over steel stud framing. Less structural steel and less concrete reduces the energy required for manufacturing and transportation and ultimately requires fewer natural resources.

Because of the light weight of the material, furring can be added to create a cavity for exterior insulation which will increase energy efficiency of the building. Mechanical contractors usually employ energy modeling software and can evaluate the long term energy savings based on this type of envelope design. Smaller and fewer attachment points also reduce thermal bridging and increase energy efficiency whether the insulation is placed inside the wall cavity or on the exterior.

StoneLite® panels are suitable for rainscreen or open joint applications. Rainscreen is particularly advantageous in climates where the temperature differential between interior air and exterior is high because it allows the wall system to dry out, eliminating the environmental conditions that support the growth of mold. In fact, the highest mold litigation state in the country is Arizona because of the cooler air inside the building and the hot air outside. This temperature differential combined with tightly sealed wall systems can produce a condensation point within the wall and support mold growth. Generally a minimum air gap of 1″ is required to provide adequate ventilation.

Almost any stone can be incorporated in the  panel system. This allows the possible benefit of regional materials credit if attention is paid to the selection of stone that is quarried within 500 miles of the project location.

The specifications can be found  on our website under the Specifications tab. The specifications are offered in two formats – pdf and Word. Word allows the specifier to create a project-specific specification.

Product Testing

The Product section of the SPI website has a Testing section that provides a summary of specific tests including, but not limited to:

  • Acid Freeze Thaw Exposure
  • Accelerated Aging
  • Shear and Flatwise Tension Bond
  • Air and Water Infiltration
  • Impact Loading
  • Blast Testing
  • Racking Shear (simulating seismic loading)
  • Wind Load Flexural
  • Vibration Loading
  • Fire, Flame Spread and Combustion
  • Attachment Systems
  • Expansion Coefficients
  • Building Code Approval
  • Quality Control

These summaries site the date of the test(s), report number, and the relevant ASTM, ICBO, UBC or other standards. Copies of the original test reports are not for general distribution, but are available on request

Both flexure and bond testing following accelerated aging procedures should be required. These tests are somewhat similar to actual exterior weathering conditions. SPI can submit complete reports of accelerated aging by acid freeze thaw procedures where the product was subjected to temperatures ranging from minus 10F to plus 170F while submerged in a 4 pH sulfuric acid bath. Our European accelerated aging procedure included UV exposure in addition to acid freeze-thaw conditions.

Tests were conducted on SPI samples that had been exposed to accelerated aging, and also on samples that had not been exposed for comparison of load capacity (flexural or bending strength) and bond of stone to honeycomb capacity (sometimes called tension capacity).

Those tests were conducted after (following) accelerated aging. They found that the flexure or bending capacity in StoneLite® panels was reduced less than 10%, whether granite or limestone or travertine. When this type of exposure and testing is conducted on solid traditional travertine or limestone, there will be a reduction of around 80% in strength. The reduction in solid granite strength will be about the same as SPI panels.

StoneLite® panels have passed the full scale multi-story fire evaluation in addition to other fire exposure tests, flame spread testing, and toxicity testing for assurance that the product will perform and will meet life-safety requirements.

StoneLite® panels will not support combustion. They have been subjected to the Standard Method of Test for Surface Burning Characteristics in accordance with ASTM E 84 with the following results:

  • Flame Spread Index: 5
  • Smoke Developed: 5
  • Fuel Contributed: 0

There’s only a small “combustible” component in StoneLite® which is in the epoxy that is only exposed if the stone face cracks. The NFPA and the ICC (International Code Council) require a Flame Spread Index or 25 or less, a smoke developed of 450 or less in order to be considered Class 1 or Class A.

According to this procedure, cement asbestos board has a flame spread index = 0, and smoke developed = 0. Untreated red oak has a flame spread = 100.

The StoneLite® panel also performed well in the Evaluation of the Acute Inhalation Toxicity tests conducted in accordance with the University of Pittsburgh Test Method. It was concluded that the panels are no more toxic than Douglas Fir wood.

Fire test reports that are available on a confidential basis include ASTM E84, ASTM E108M, and NFPA 285. The UK fire test BRE BS 8414-2 is also available.

StoneLite® panels offer superior protection against failure due to seismic movement as compared to much heavier and more brittle dimensional stone.

Racking shear tests simulating seismic loading were conducted and passed in accordance with ASTM E-695. Reference Ramtech Laboratories Report No. 8125-87.

Racking shear tests were conducted on StoneLite® panels attached to steel stud framing with epoxy-set threaded inserts bolt attached to clip angles. The 8-ft. x 8-ft. assemblies were loaded to over 5,000 lbs. producing deflections of 2 1/2 inches. There was no major chipping nor damage, no disengagement, and no bond loss. When loaded to failure, the connection clips distorted and there was connection clip weld failure on the back-up framing.

Following the 1995 bombing of the A.P. Murrah Federal Building in Oklahoma City, the General Services Administration (GSA) established Security Criteria for glazing in all federal buildings. The establishment of these criteria has resulted in the increased use of blast resistant fenestration products in federal courthouses and similar government buildings.

In order to expand the use of these criteria beyond the GSA, the Interagency Security Committee (ISC) developed the ISC Security Criteria. The ISC Security Criteria was adopted and approved for use in all GSA new buildings and major modernization projects. It requires that windows and wall assemblies be designed to mitigate the hazard from flying fragments (projectiles) in the case of an explosive event. The intent of these criteria is to reduce (not necessarily eliminate) the potential hazards, recognizing that not all windows and wall assemblies will survive a bomb attack.

These criteria require that assemblies meet performance levels that correspond to specific levels of protection. Most GSA facilities fall under the Class “C” Threat Level for blast resistance. This correlates to a peak air blast pressure of 4 psi and a maximum positive phase impulse pressure of 28 psi-msec.

SPI’s StoneLite® panels underwent a Full scale Blast Test subjecting the SPI system to 8 psi air blast pressure and 49 psi-msec positive phase impulse. The initial positive blast load caused a deflection of about 2 inches, and then a milli-second later the negative load caused a deflection of about 3 inches. Following the test, there were no cracks, no chips, and no damage whatsoever in either the limestone or the granite panels.

The actual blast test can be viewed here.

Following Hurricane Andrew, the South Florida building code was modified to add another test due to the massive devastation created by flying debris. In the test, StoneLite® panels were subjected to a 90 psf cyclic positive-negative wind loading 1,342 times, then taken to a maximum of 135 psf.

A 2″ x 4″ x 8′ timber stud is fired several times at the panel at 50 ft. /sec. This simulates a house stud being thrown in a 100 m.p.h. wind following wind cycles of 190 m.p.h. with gusts up to 230 m.p.h.

Stone Panels’ system easily passed the hurricane wind and large missile impact requirements of Miami-Dade Florida building authority. SPI was the first U.S. lightweight reinforced stone manufacturer having South Florida building authority acceptance and have held the certification for many years.

Stone Panels International LLC is also the only lightweight reinforced stone supplier having acceptance by the International Code Council (ICC) who write the model building code. Their evaluation service division representatives visit our factory at least four times each year, unannounced, for assurance that the product and production procedures are unchanged from product that was manufactured for testing. They collect samples for on-going testing for assurance that we continue to meet their requirements.

Without that continuing third party control, a superior product could be produced for testing and a cheaper product manufactured for construction. The construction industry can be assured of a quality system that will not fail only if they require building code authority acceptance.

As a matter of interest, Stone Panels International LLC is also the only lightweight stone system accepted by the British Board of Agrèment for construction in the UK and by the Avis Technique for construction in France and other countries.

Details and Attachments

SPI has been manufacturing StoneLite® panels with a fixed curve for over 25 years. The oldest exterior curved panels in the U.S. are on Kimbrough Hall, Washington State University in Pullman, WA, completed in 1988. The building is clad with Chantilly (French) limestone with an 18-ft. radius. SPI would prefer to limit the amount of radius on exteriors to 20-ft. for limestone and 40-ft. or more for granite and marble, especially if the stone is on the exterior side of the curve.

SPI supplied a significant amount of curved marble for the interior of the Thomas F. Eagleton Federal Courthouse in St. Louis in 2000. Traveling exhibits for Infinity and Rolex also incorporated curved limestone and marble.

StoneLite® panels are frequently installed in rainscreen or open joint construction. The majority of all SPI installations in Europe and in Canada are rainscreen. On some projects the joints are left totally open. Other projects may want gasketing material installed in the joints to keep insects out and minimize the amount of dirt that enters the cavity between the backside of our panel and the weather barrier. There are no hard set rules for rainscreen construction.

SPI does suggest attaching a vertical baffle between the StoneLite® panel and the weather barrier at all corners. The baffle can be either light gauge aluminum angle or Z-section. It provides or aids in providing pressure equalization. There can be positive wind load on any given elevation, but negative wind on an adjacent elevation. Without a baffle, higher pressure air and moisture will enter on the high pressure side, and exit on the lower pressure (or negative pressure) elevation, resulting in excessive water being drawn into the cavity.

SPI also suggests sealing the joints in all horizontal surfaces, again to prevent migration of air and water from a high pressure to a low pressure area.

Stone Panels International LLC normally supplies painted interlocking channel (ILC) aluminum extrusions for all installations in the US. The paint works as an insulator to prevent electrolytic action between aluminum and other materials including steel. Self-drilling, self-tapping screws (supplied by others) are used for attaching ILCs to back-up framing. SPI recommends attachment of ILCs using neoprene washer head fasteners to prevent direct contact between a steel screw and the aluminum. SPI recommends corrosion resistant screws.

Anodized aluminum ILCs are typically supplied for rainscreen installations in Europe and Canada.

The StoneLite® system is suitable and designed for ceilings and soffits.

The installation procedure for a ceiling or soffit is nearly the same as the procedure for walls, except that interlocking channels are attached to horizontal framing rather than vertical framing. SPI does recommend provisions to prevent the panels from disconnecting if there is the possibility of a panel sliding horizontally out of the installed location.

SPI includes lengths of interlocking channels for the installer to attach to the ceiling or soffit framing. Panels are delivered with interlocking channel clips to engage in the long field installed members.

StoneLite® panels may be extended below grade as they can be exposed to moisture without deterioration. There are two concerns which should be considered. If using a soft stone like limestone, moisture will wick up and stain the stone face and salt (often used on sidewalks in the winter) will etch the face of limestone. In these instances, it is preferable to go with granite at the base. If there is heaving from frost, there should be a buffer between the stone and grade material.

There is no seal needed at the perimeter of StoneLite® panel, whether caulked joints or open (rainscreen) joints.

StoneLite® panels are often utilized in a wet location, such as a water feature or in an open joint exterior application. Consideration should be given to the potential reaction of the stone to any chemicals inherent in municipally supplied water.

There are a number of ways that signs can be mounted on StoneLite® panels. Costs and ease of installation vary dramatically. Contact us to discuss relative cost and design considerations of these systems.

StoneLite® panels have been used to cover doors. The normal procedure is to attach a light gauge angle (20 gauge) at the bottom of the door for gravity support. Then the panels are attached to the door with adhesive – structural silicone if a metal door. The architect will normally want a finished corner at both jamb and hinge vertical edges. The panels are 5/8″ thick (3/8″ honeycomb), and the structural silicone is about 3/16″ thickness.


The use of natural stone in construction presents the designer with difficult choices when considering the finite availability of a dwindling natural resource. Heavyweight stone cladding accelerates the consumption of this finite raw material, which, in turn, has a necessarily adverse impact on sustainability.

Because the manufacturing process produces a panel with a thin veneer of stone, StoneLite® panels can use up to 85% less finite raw material. Designers have the benefit of knowing that natural stone reserves are being conserved without compromising the aesthetic quality of their building designs.

StoneLite® panels represent the most sustainable natural stone cladding option available in the construction industry today.

While individual construction materials can be evaluated for their impact on the environment and sustainability, their impact on other associated materials within the building structure also carry their own implications.

StoneLite® panels weigh less than 3.5 lbs./sq.ft. Their lightweight properties make it possible for designers and engineers to take this into account when calculating the overall loading on any given building. Substantial reductions in the structure and foundations of a building are possible and this can have a profound effect on the amount of steel and concrete required. This, in turn, makes it possible to reduce a building’s environmental impact when taking into account the energy consumption involved in the production and manufacturing of those materials.

StoneLite® panels use aluminium channels in the manufacturing of the attachment system. The company acts in partnership with its approved supplier who must be able to demonstrate that the aluminium content of their product is manufactured from at least 75% recycled raw material.

The panels have the ability to be fully demounted and can be installed on more than one building during the life cycle of the product.

The water used throughout the manufacturing process is constantly recycled and the stone dust is settled out through filtering systems where it can be reused as dirt stabilization and road base material. This attention to detail ensures that waste product from the manufacturing process is not returned into the environment, but can be utilized by associated industry.

Caulking and Sealants

In the United States, an exterior application usually requires that the joints be sealed. In that event we suggest 3/8″ wide joints with an open cell backer rod and silicone sealant.

Silicone sealant is recommended (there are several manufacturers) because it does not deteriorate due to UV and high temperatures. Dark color stone in particular can reach surface temperatures exceeding 160° F in direct sunlight, even if the ambient temperature is below 80° F. Polyurethane sealants will break down at about 140° F.

It is recommended that the sealant supplier conduct accelerated aging tests to determine if there might be bleeding of the sealant carrier into the stone, and the sealant supplier should also recommend a primer that won’t bleed into the stone. The customer should require a sealant warranty for bond to stone and also a warranty against staining from the sealant supplier.

For interior applications, a ¼” joint is possible. In addition, an acrylic joint sealant is acceptable for interior applications because they don’t need to seal the joint against moisture penetration. Acrylic sealant material won’t stain the stone and it gets harder.

Silicone sealant cures or firms up when it is exposed to moist air. When the cure is accelerated by excessive moisture or temperatures over about 120° F, it will “gas”. The small gas bubbles quickly increase in size if the sealant is heated when the sealant has not yet cured.

Gassing and resulting bubbles in sealant occur most often during wet damp weather, and when there’s direct sunlight shining on the wall. It’s especially common in late winter and spring time of year. Darker color stones can reach temperatures exceeding 160º F in direct sunshine, even though the ambient temperature might be only 80° F.

Some sealant product information sheet states that it should not be used when the surface temperature exceeds 122° F. They also say it should not be used on frost-laden or wet surfaces. It is important for the contractor to check the literature of all silicone sealant manufactures.

It’s possible for gassing to occur if a closed cell backer rod is used. The skin on that backer rod can be easily torn and gas then gets into the sealant. It is suggested to use an open cell backer rod.

Silicone sealants generally have a shelf life of 12 months if stored below 80° F.

There are several suppliers of stone sealer and graffiti control products. When stone sealer has been applied, the amount of moisture absorbed into the stone is reduced. In a dirty environment, dust settles on the stone surface. Water on the surface of a porous stone such as limestone will carry some dirt into the stone pours, but a sealer reduces the absorption.

Graffiti control adds a film to the stone surface. Graffiti can then be removed with hot water power wash or with chemical similar to MEK. Graffiti control should be removed and reapplied every 4 to 5 years, or as recommended by the supplier.

Sanded grout will work with Stone Panels products as well as with tile. It will not provide a water-tight joint seal, but it is fine for interior applications and for construction including a weather barrier behind the panels.

Sanded grout would not provide a watertight seal with our panel, therefore a moisture barrier would be required behind our panels if it is used on a building exterior.