# 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.