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Siding and Cladding Problems

Stucco

Problem: Moisture damage inside the wall assembly.

Cause: Entry of rainwater and snow through cracks in the stucco.

Like other masonry products, stucco can develop cracks due to improper curing, improper mixing, or lack of accommodation for expansion and contraction.

Solutions: Ensure that the stucco has a proper mix and is properly cured.

  • Follow the manufactures instructions for proper mix requirements.
  • Water must be clean and free of contaminants and should be added at ratios identified in Table 1. The addition of too much water to the mix will weaken the stucco and can result in excessive shrinkage.
Table 1 - Stucco Mixes by Volume

Portland Cement

Masonry Cement

Type H

Lime

Aggregate

1

-

0.25 to 1

3.25 to 4 parts per part of cementitious material

1

1

-

  • The addition of plasticizers can improve workability.
  • Allow enough time between coats to promote good curing. Follow the manufacturer's installation recommendations.

Provide movement joints to accommodate normal shrinkage in the wall framing.

  • Framing lumber will normally shrink as it dries after construction most noticeably at floor header assemblies. Provide a movement joint, with appropriate flashings, above the floor header to accommodate structural movement as shown in Figure 54.

Wall Movement Joints At Floor Header

Figure 54 - Wall Movement Joints At Floor Header

lath fasteners

Figure 54b - Lath fasteners

Stucco Lath Nailing Patterns

Figure 55 - Stucco Lath Nailing Patterns

  • Reinforce metal lath at the corners of buildings and wherever the stucco is returned at window and door openings.
  • Use a vertical strip of lath or reinforcement extending not less than 6 inches (150 mm) from either side of the corner. Alternatively, overlap lath at corners by a minimum of 6 inches (150 mm).

Stucco over lath

Figure 55b - Stucco over lath

Fully embed the stucco lath in the stucco.

  • Where the stucco lath is not adequately covered (embedded) after installation of the three required coats of stucco, the lath can rust. Rusting will result in expansion of the space taken up by the lath and in cracking of the exterior surface of the stucco.
  • Metal lath should be completely covered by the first, or base coat of the stucco.

Continued.......