ASTM International
ASTM C926 / C1063 (plaster & lath)
ASTM C926 and C1063 describe how Portland cement plaster (stucco) and its lath are installed: the water-resistive barrier behind the lath, how the lath is fastened and lapped, the three-coat build and its thickness, and the joints and screeds that let the assembly move and drain. Most stucco failures trace to what is behind the first coat, so the walk lives at lath and barrier stage before the scratch coat covers it.
Adoption varies by jurisdiction. Confirm the edition your authority having jurisdiction enforces before you run a walk against it.
What it covers
- Water-resistive barrier layers, laps and integration with flashing
- Lath type, attachment, laps and furring off the substrate
- Three-coat application and coat thickness
- Control and expansion joint layout and embedment
- Weep screeds and drainage at terminations
- Curing and moist-conditioning between coats
What the evidence looks like
- Water-resistive barrier photographed lapped shingle-fashion and tied into flashing before lath covers it.
- Lath attachment and furring shown fastened to framing, not floating on the barrier, with laps in frame.
- Weep screed photographed set at the base with the barrier lapped over its flange, not tucked behind it.
- Control and expansion joints documented located and embedded before the coat that hides them.
- Coat thickness and moist-cure between coats recorded as applied and dated rather than asserted.
Checklists that verify work against ASTM C926 / C1063 (plaster & lath)
3 free checklists, each with the photo every item needs before it can be submitted.
Portland cement plaster (stucco) Rough-in· Portland cement plaster (stucco)Portland cement plaster (stucco) rough-in inspection checklistWater-resistive barrier, lath and accessories verified before the scratch coat covers them6 items11 photosPortland cement plaster (stucco) Final· Portland cement plaster (stucco)Portland cement plaster (stucco) final inspection checklistThree-coat thickness, cure between coats and finish uniformity verified after the finish coat6 items10 photosPortland cement plaster (stucco) Punch· Portland cement plaster (stucco)Portland cement plaster (stucco) punch checklistCloseout walk for cracking, hollow lath areas and patch blending4 items6 photos
Common questions
- What is ASTM C926 / C1063 (plaster & lath)?
- Portland cement plaster and lath: water-resistive barrier and lath attachment, coat thickness, joints and weep screeds. It is published by the ASTM International. ASTM C926 and C1063 describe how Portland cement plaster (stucco) and its lath are installed: the water-resistive barrier behind the lath, how the lath is fastened and lapped, the three-coat build and its thickness, and the joints and screeds that let the assembly move and drain. Most stucco failures trace to what is behind the first coat, so the walk lives at lath and barrier stage before the scratch coat covers it.
- What does ASTM C926 / C1063 (plaster & lath) cover?
- Water-resistive barrier layers, laps and integration with flashing; Lath type, attachment, laps and furring off the substrate; Three-coat application and coat thickness; Control and expansion joint layout and embedment; Weep screeds and drainage at terminations; Curing and moist-conditioning between coats.
- What does a field inspection against ASTM C926 / C1063 (plaster & lath) look at?
- Water-resistive barrier photographed lapped shingle-fashion and tied into flashing before lath covers it. Lath attachment and furring shown fastened to framing, not floating on the barrier, with laps in frame. Weep screed photographed set at the base with the barrier lapped over its flange, not tucked behind it. Control and expansion joints documented located and embedded before the coat that hides them. Coat thickness and moist-cure between coats recorded as applied and dated rather than asserted.
- Which edition of ASTM C926 / C1063 (plaster & lath) applies to my project?
- Adoption varies by jurisdiction. Confirm the edition your authority having jurisdiction enforces before you run a walk against it.
- Which checklists verify work against ASTM C926 / C1063 (plaster & lath)?
- 3 free checklists in the RTI library reference this family. Each is listed on this page with the photo evidence every item needs before it can be submitted.
A standard is only met if the evidence exists
RTI holds the submit button until every mandatory item is answered and the photos are attached, then chains the record so it can be proven untouched later.