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Title: Section 2509  •  Size: 4646

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SECTION 2509 - EXPOSED AGGREGATE PLASTER

2509.1 General. Exposed natural or integrally colored aggregate may be partially embedded in a natural or colored bedding coat of cement plaster or gypsum plaster, subject to the provisions of this section.

2509.2 Aggregate. The aggregate may be applied manually or mechanically and shall consist of marble chips, pebbles or similar durable, nonreactive materials, moderately hard (three or more on the Measure of Hardness scale).

2509.3 Bedding Coat Proportions. The exterior bedding coat shall be composed of one part portland cement, one part Type S lime and a maximum three parts of graded white or natural sand by volume. The interior bedding coat shall be composed of 100 pounds (45.4 kg) neat gypsum plaster and a maximum 200 pounds (90.7 kg) of graded white sand, or exterior or interior may be a factory-prepared bedding coat. The exterior bedding coat shall have a minimum compressive strength of 1,000 pounds per square inch (6894.8 kPa).

2509.4 Application. The bedding coat may be applied directly over the first (scratch) coat of plaster, provided the ultimate overall thickness is a minimum of 7/8 inch (22 mm), including lath. Over concrete or masonry surfaces the overall thickness shall be a minimum of 1/2 inch (13 mm).

2509.5 Bases. Exposed aggregate plaster may be applied over concrete, masonry, cement plaster base coats or gypsum plaster base coats.

2509.6 Preparation of Masonry and Concrete. Masonry and concrete surfaces shall be prepared in accordance with the provisions of Section 2508.8.

2509.7 Curing. Cement plaster base coats shall be cured in accordance with Table 25-F. Cement plaster bedding coat shall retain sufficient moisture for hydration (hardening) for 24 hours minimum or, where necessary, shall be kept damp for 24 hours by light water spraying.

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