Perlite is not a trade name but a generic term for naturally occurring siliceous volcanic rock. The distinguishing feature which sets perlite apart from other volcanic glasses is that when heated to a suitable point in its softening range, it expands from four to twenty times its original volume.

This expansion process is due to the presence of two to six percent combined water in the crude perlite rock. When quickly heated to above 1600 F (870 C) the crude rock pops in a manner similar to popcorn as the combined water vaporizes and creates countless tiny bubbles in the softened glassy particles. It is these tiny glass-sealed bubbles which account for the amazing lightweight and other exceptional physical properties of expanded perlite.

The expansion process also creates one of perlite's most distinguishing characteristics: its white color. While the crude perlite rock may range from transparent to light gray to glossy black, the color of expanded perlite ranges from snowy white to grayish white.

Expanded perlite can be manufactured to weigh from 2 lbs/ft3 (32 kg/m3) to 15 lb/ft3 (240 kg/m3) making it adaptable for numerous uses, including filtration, horticultural applications, insulation, inert carriers and a multitude of filler applications.

The unique properties of expanded perlite make it particularly useful in the manufacture of a variety of oil and water based textured coatings

Advantages of Perlite

Perlite offers advantages to both manufacturers and applicators of textured coatings. To manufacturers, perlite provides low cost bulk filling, low oil adsorption and a snowy white color to reduce pigmentation costs. In addition, special grading provides a measure of quality control to textured coatings and minimizes dust. Because perlite is light in weight, shipping and handling costs are reduced.

The lightweight of perlite textured coatings reduces the tendency of thick films to sag and run. As a result, applicators can apply heavier coatings in a single pass with subsequent labor savings. In addition, because perlite is inorganic and inert, it does not contribute to yellowing in industrial atmospheres. Even as a coating, applicators can benefit from perlite's unique insulating properties.

*Particle size ranges are approximate and presented for guidance only.
Trials are suggested to determine materials for the desired effect.
Blends of different grades also may be useful.

Textured Coating Formulation

Textured coatings utilizing the unique properties of perlite may be formulated for spray application and roller application. On a volume basis, significant quantities of perlite may be used to produce distinctive textures. In addition to lowering the cost of coatings, a reduction in weight also can be attained because of the low density of perlite.

Trials should be conducted to determine the optimum amount of perlite necessary to achieve the desired texture.

Aggregate Blending

Expanded perlite is a mineral aggregate and the coarser particle sizes will not permit high shear rates during mixing. Slow speed mixing with broad paddles is recommended. Mixer horsepower requirements would be approximately 10 horsepower per 250-gallon (1000-liter) batch at mixing speeds in the range of 50-200 rpm. Formulations requiring a high level of shear should be mixed with high-speed equipment prior to the addition of perlite. Provisions should be made to allow for 40% bulking while perlite is being added to the coating mix.

Application of Perlite Textured Coatings

Heavy-duty spray equipment should be used to apply perlite-textured coatings. Typical tip sizes are:

When coatings are to be applied with rollers, 3/4 to 1-1/4 (18-30mm) long nap rollers or a honeycomb foam roller should be used for fine and medium textures. For bold textures, a deeply patterned roller is recommended for best results.

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