Putty formulations utilize a variety of raw materials, including primary components such as heavy calcium carbonate, cement, calcium hydroxide, gypsum powder, bentonite, and quartz powder, as well as auxiliary materials like polymer powders, cellulose ethers, and polypropylene (PP) fibers. Below are the key quality control and testing methods for these materials.
1. Heavy Calcium Carbonate (CaCO₃)
Heavy calcium carbonate powder is mechanically ground from natural carbonate minerals (e.g., calcite, dolomite, marble). It offers excellent thermal stability, high whiteness, and low oil absorption. Common fineness grades include 100-mesh (single fly ash), 200-mesh (double fly ash), and ultra-fine powder (≥1250 mesh).
Quality Control:
- Calcite: High crystallinity, fine texture, and smooth finish, ideal for high-gloss putty.
- Dolomite, etc.: Lower crystallinity, coarser texture, suitable for standard putty.
Testing Methods:
- Visual inspection: Calcite exhibits higher bulk volume and smoother feel; non-calcite powders are denser and more abrasive.
- Application test: Calcite-based putty achieves a polished finish more easily.
2. Calcium Hydroxide (Ca(OH)₂)
Produced by the reaction of quicklime and water, this white powder is slightly soluble in water and strongly alkaline.
Quality Control:
- High whiteness, minimal impurities, fine particle size, low moisture content, and low bulk density.
Testing Methods:
- Visual assessment for color and impurities.
- Moisture content and bulk density testing.
3. Cement
A primary binder in exterior putty, with recommended types being 42.5P.W white Portland cement or 42.5P.O ordinary Portland cement.
Quality Control:
- Select reputable brands to ensure strength and consistency.
Testing Methods:
Setting time, compressive strength, and water resistance tests.
4. Gypsum (CaSO₄·2H₂O)
Used in gypsum-based putty, with β-hemihydrate gypsum (building plaster) being the preferred form.
Quality Control:
High whiteness, uniform fineness, and stable setting time.
Testing Methods:
Setting time, mechanical strength, and impurity analysis.
5. Sodium Bentonite
A montmorillonite-based clay that enhances viscosity and thixotropy.
Quality Control:
Natural sodium bentonite with high whiteness, colloidal value, and swelling capacity is preferred.
Testing Methods:
Swelling index, dispersibility, and colloidal value tests.
6. Polymer Powder
A critical binder in putty formulations, including redispersible polymer powders (e.g., VAE, acrylic) and polyvinyl alcohol (PVA) powders.
Quality Control:
High adhesive strength, stability, and environmental safety.
Testing Methods:
Bond strength tests, solution stability evaluation, and eco-toxicity assessments.
7. Cellulose Ethers
Common types include hydroxypropyl methyl cellulose (HPMC) and carboxymethyl cellulose (CMC), which influence water retention and workability.
Quality Control:
Stability is prioritized over viscosity; select products with good solubility and minimal impurities.
Testing Methods:
Aqueous solution viscosity and stability tests.
8. PP Fibers
Used in exterior putty to improve crack resistance.
Quality Control:
O-type fibers (diameter ~20 μm, tensile strength ≥400 MPa, length 2–3 mm) are preferred for optimal dispersion and reinforcement.
Testing Methods:
Fiber morphology inspection, tensile strength testing, and dispersion evaluation to detect adulterants (e.g., oil or water).
