R703.7 Exterior Plaster (Stucco)
Lath and lath attachments shall be of corrosion-resistant materials. Expanded metal or woven wire lath shall be attached with 11/2-inch-long (38 mm), 11-gage nails having a 7/16-inch (11.1 mm) head, or 7/8-inch-long (22.2 mm), 16-gage staples, spaced not more than 6 inches (152 mm) or as otherwise approved.
Plastering with cement plaster shall be in accordance with ASTM C926. Cement materials shall be in accordance with one of the following:
- Masonry cement conforming to ASTM C91 Type M, S or N.
- Portland cement conforming to ASTM C150 Type I, II, or III.
- Blended hydraulic cement conforming to ASTM C595 Type IP, IS (< 70), IL, or IT (S < 70).
- Hydraulic cement conforming to ASTM C1157 Type GU, HE, MS, HS, or MH.
- Plastic (stucco) cement conforming to ASTM C1328.
Plaster shall be not less than three coats where applied over metal lath or wire lath and shall be not less than two coats where applied over masonry, concrete, pressure-preservative-treated wood or decay-resistant wood as specified in Section R317.1 or gypsum backing. If the plaster surface is completely covered by veneer or other facing material or is completely concealed, plaster application need be only two coats, provided the total thickness is as set forth in Table R702.1(1).
On wood-frame construction with an on-grade floor slab system, exterior plaster shall be applied to cover, but not extend below, lath, paper and screed.
The proportion of aggregate to cementitious materials shall be as set forth in Table R702.1(3).
Water-resistive barriers shall be installed as required in Section R703.2 and, where applied over wood-based sheathing, shall include a water-resistive, vapor-permeable barrier with a performance at least equivalent to two layers of Grade D paper. The individual layers shall be installed independently such that each layer provides a separate continuous plane and any flashing, installed in accordance with Section R703.4 and intended to drain to the water-resistive barrier, is directed between the layers.
Exception: Where the water-resistive barrier that is applied over wood-based sheathing has a water resistance equal to or greater than that of 60-minute Grade D paper and is separated from the stucco by an intervening, substantially nonwater-absorbing layer or designed drainage space.
Each coat shall be kept in a moist condition for at least 48 hours prior to application of the next coat.
Exception: Applications installed in accordance with ASTM C926.