Expanded Perlite for Textured Coatings

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

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.

Perlite is available in different grades ranging from fine to coarse material. The table below provides general guidance on textures that may be achieved with different perlite particle sizes.

PERLITE PARTICLE/TEXTURE RELATIONSHIPS
Perlite Particle Size*	Degree of Texture
0.0-0.2 mm	Very fine or nontextured finishes
0.1-3.0 mm	Normal Textured Finishes
1.5-6.0 mm	Very bold textures
*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 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.

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.

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

Bold Textures	3/8 to 1/2 inch (8-12 mm)
Medium (Normal) Textures	3/16 to 1/4 in. (5-6 mm)
Fine Textures	1/8 to 3/16 in (3-5mm)

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.