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projects/sag-mesh-plane-v0u1/mp-rapid-set-cement-mortar.md

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+# Material Passport — Rapid-Set Cement Mortar
+
+**File:** `mp-rapid-set-cement-mortar.md`
+
+**1. Material Name**
+Rapid-set cement mortar (e.g., “Cement All”).
+
+**2. Source Type**
+☑ Perennial Secondary Market (building trades, hardware stores).  
+☑ Industrial Junk Stream (construction sites often discard partial bags).
+
+**3. Physical Specs**
+- Type: pre-mixed hydraulic cement with additives.
+- Form: dry powder, grey or off-white.
+- Bag sizes: typically 5–25 lbs (2–11 kg).
+- Compressive strength: ~4000–6000 psi (brand-dependent).
+- Set time: 15–60 minutes; practical handling after ~1–2 hours; fuller cure ~24 hours.
+
+**4. Substitute(s)**
+- Plaster of Paris / Perfect Cast (lighter, weaker, faster).
+- Standard Portland cement mortar (slower, stronger, heavier).
+- Lime plaster (softer, brittle, low strength).
+
+**5. Known Limitations**
+- Brittle under impact.
+- Shrink cracks possible if cast too thin.
+- Moisture sensitive before curing; absorbs water after curing.
+
+**6. Hazards**
+- Alkaline dust: skin/eye irritant; gloves and goggles recommended.
+- Exothermic curing; prolonged skin contact may cause burns.
+- Store sealed: absorbs humidity and hardens in bag.
+
+**7. Visual Reference**
+*(Add a photo of a typical retail bag with label visible.)*
+
+**8. Declared Use in Design**
+Acts as structural bulk fill for the **Sag-Mesh Plane v0.1**. Provides stiffness and flatness; PLA mesh provides geometry and keying. Central compromise: chosen because it’s cheap, plentiful, and globally ubiquitous—at the cost of brittleness and lack of tensile reinforcement.