JAIC 1998, Volume 37, Number 1, Article 6 (pp. 69 to 87)
JAIC online
Journal of the American Institute for Conservation
JAIC 1998, Volume 37, Number 1, Article 6 (pp. 69 to 87)

FILLS FOR WHITE MARBLE: PROPERTIES OF SEVEN FILLERS AND TWO THERMOSETTING RESINS

ELEONORA E. NAGY



2 MATERIALS AND SAMPLE PREPARATION


2.1 SOURCES OF MATERIALS AND THEIR DATA

Materials were provided directly by their manufacturers. Fresh natural calcite marble and marble dust were obtained from a commercial distributor (see Sources of Materials). The decayed marble originated from a broken gravestone.

Particle sizes for each material were measured by the author. Refractive indices for the two thermosetting resins were kindly provided by Christopher W. McGlinchey. All other information was obtained through literature or communication with the manufacturer.

Sikadur 35, Hi-Mod LV—A two-component, solvent-free, very low viscosity (375 centipoise [cps]), high-strength, multipurpose epoxy resin adhesive. It has a clear amber color and a pot life of about 25–30 minutes. The full cure of the resin is close to complete in 72 hours but absolutely complete only in 7 days. The resin-to-hardener mixing ratio is 2:1. The RI of the cured resin is 1.567.

Akemi Marmorkitt 1000/Akemi Marble Filler 1000 Transparent/Clear Flowing—A water-clear, 680 cps viscosity, two-component polyester adhesive, specifically produced as an adhesive for stone (“for Carrara marble, Ajax, Onyx translucent, and Greek Thassos marble”). It has a pot life of approximately 7–10 minutes and a full cure time of 48 hours (Akemi Plastics 1988). The resin-to-hardener mixing ratio is 100:3, and the cured resin has an RI of 1.525.

Calcium Carbonate (Marble-fil) 151C—A white, low-cost, high-loading filler. This precipitated type of calcium carbonate has the finest and most uniform particle size of all the fillers that were tested. The diameter of the anisotropic, rounded hexagonal, rhombohedral particles is between 0.5–1.5 microns (μ). The RI is between 1.47 to 1.69 (mean 1.66), loose density 2.0 g/cm3.

Cab-o-sil (fumed silica)—An anisotropic, white, extremely lightweight filler containing 99.9% silicon dioxide. It is practically free of contaminating metallic salts. The rounded, rough-surfaced agglomerates range from 0.5–120μ in size, the average being ca. 40μ. The mean RI is 1.54 (1.47–74), loose density 0.03 g/cm3.

Wet-ground Mica 160—A grayish brown mineral additive (H2KAl3[SiO4]3) with a solid, delaminated, rounded rectangular, transparent flake structure. The average flake size is 6–10μ. The smallest flakes are 1μ; the largest particles are 30μ in diameter. The birefringent particles have refractive indices of 1.552, 1.582, and 1.588. The loose density is approximately 0.3 g/cm3.

Marble Dust—One of the most popular resin additives for marble fills. The average size of the block-shaped particles is about 250μ, with a large particle size distribution ranging from approximately 20 to 800μ. The average RI of the birefringent particles is 1.65. Loose density 1.65 g/cm3.

Globe-o-sil G—Has a white granular appearance. The neutral pH, low-density additive contains 71–75% silicon dioxide. The foamed particles (1–80μ) enclose cells that are separated by thin, glassy membranes. When mixed with resins, the enclosed air is held and sealed within the glassy membranes. The anisotropic particles tend to form lumps (ca. 60μ) that make up the average size particles. The mean RI is 1.45, loose density 0.11 g/cm3.

Microspheres 409—A brand name for glass microballoons, which are hollow sodium borosilicate microspheres with a white powdery appearance. The particle size is 1–140μ, with an average of 50μ. The product contains some broken particles and impurities. The particles are isotropic, and the RI is 1.52. The loose density is 0.09 g/cm3.

Eccospheres IG 101—Hollow sodium borosilicate glass spheres from 5–150μ in diameter. The average size of this type of glass microballon is 55μ. The RI of the isotropic spheres is 1.52. The loose density of Eccospheres is 0.17 g/cm3. The major difference between Microspheres and Eccospheres filler is that the latter is a more refined product and does not contain broken spheres or impurities. (Note that some birefringence is present in both Microspheres and Eccospheres due to the enclosed air in the hollow spheres.)

Fresh Natural Marble Specimens and Decayed Marble Specimens (4 each)—Used as a control for the duration of the tests. X-ray diffraction of the fresh natural marble specimen was performed at the Miller Museum of Geology (Badham 1991), and the results matched the mineral calcite almost perfectly. Both fresh and decayed marble specimens had a whitish color with very faint grayish veins. The decayed marble had a sugary, slightly discolored, grayish crust formation from outdoor exposure (approximately 1/8 in. thick) on the surface of the stone.


2.2 SAMPLE PREPARATION

All natural marble samples and controls were cut and prepared by the author. For marble dust, a piece of the fresh calcite marble was crushed using a Jaw Crusher (Braun Chipmunk VD67) and a Bico Pulverizer (disk mill by Bico, Inc.) at the Geology Department of Queen's University, Kingston, Canada.

Composites and pure resin samples were made using a Plexiglas lattice open at the bottom and the top. Components of the resins were mixed according to the manufacturer's instructions. Then the filler was added, and the mixture was poured or pressed into the cells of the lattice. Renaissance microcrystalline wax was used as a separating agent. Samples for a given concentration were usually made in a single batch. The samples were left to cure for one week, then pressed out from the lattice by hand.

The surfaces of the samples were sanded using 80 and 120 carat electroplated finishing sandpaper. The only exception was the sugary crust on the decayed marble. This weathered surface was not sanded and was used later for test purposes. The final size of all samples tested was 25.4 50.8 14.3 mm (1 2 9/16 in.).

Unexpected mixing difficulties with a number of fillers occasionally resulted in slightly different filler-to-resin concentrations. These concentrations remained fairly similar and are still comparable.

Materials for composites and controls were stored in a laboratory environment for 14 days at 73 4F (23 2C) at 50% 2 relative humidity before sample preparation. The samples remained in these conditions for the duration of the tests.

Samples are described as weight-volume percent (w/v): weight of resin (gram)/volume of filler (ml) 100. A low percentage concentration indicates small amount of resin with a large amount of filler in the composite. Each datum provided is the mean of a minimum of three readings for each of the three samples.


Copyright 1998 American Institute of Historic and Artistic Works