Polyacrylamide (PAM) is a common additive for viscosity enhancement, water retention and thickening in putty powder production. Anionic PAM dominates practical application, with molecular weight ranging from 12 million to 18 million and a dosage of 0.5–2 kilograms per metric ton of finished putty. It drastically optimizes workability and bonding strength of putty mortar.
I. Core Functions
- Thickening & Viscosity Boost: Forms a high-molecular reticular structure to thicken mortar, preventing sagging and dropping during troweling while improving adhesion between putty coat and base wall.
- Water Retention & Retarded Drying: Locks free moisture inside mortar and slows surface dehydration, avoiding cracking, peeling and powder fallout triggered by inconsistent drying shrinkage between surface and inner layers.
- Improved Constructability: Boosts mortar lubricity for effortless troweling and easy finishing, raising on-site construction efficiency.
- Enhanced Flexibility: Moderately improves the flexibility of cured putty to minimize cracking caused by thermal expansion and cold contraction.
II. Applicable Grades & Product Selection
Anionic polyacrylamide is the preferred option for putty formulas; cationic and nonionic variants are not recommended.
1. Ionic Classification
- Anionic PAM: Features excellent compatibility with raw materials including calcium hydroxide, cement and ground calcium carbonate, delivering outstanding viscosity build-up, water retention and anti-sagging performance, making it the mainstream choice.
- Cationic PAM: Reacts flocculantly with negatively charged components in putty system, causing lump formation and reduced mechanical strength; strictly prohibited for regular putty production.
- Nonionic PAM: Poor thickening efficiency and high unit cost; only used in small batches for special flexible putty rather than conventional mass production.
2. Matching Molecular Weight
- Interior putty based on calcium hydroxide: 15 million–18 million molecular weight (focus on smooth workability, crack resistance and water retention)
- Exterior waterproof cement-based putty: 12 million–15 million molecular weight (balances mechanical strength and constructability to avoid excessive stickiness)
3. Physical Form
Select instant-dissolving powder with mesh size of 40–80 mesh to reduce agglomeration during dissolution.
III. Two Feeding Methods
1. Aqueous Solution Addition (Recommended for uniform dispersion and stable performance)
- Prepare PAM solution: Use warm water at 40–50℃ to prepare 0.5%–1% PAM aqueous solution. Add powder slowly under low-speed water agitation to avoid caking.
- Dissolution process: Keep continuous stirring for 30–60 minutes until fully dissolved with no visible solid particles, then leave still to eliminate foam.
- Mortar blending: Add prepared PAM solution proportionally while mixing putty with water, then agitate for another 5–10 minutes prior to application.
2. Dry Powder Co-mixing (Common for factory mass production)
Blend dry PAM powder with other raw materials in high-speed mixers during putty powder manufacturing.
Drawback: Uneven dispersion with local caking risk, requiring high-performance mixing equipment.
IV. Advantages & Alternatives
- Merits: Powerful viscosity increment, superior water retention, smooth construction performance, low additive dosage and cost-effective value.
- Alternatives: HPMC, starch ether and guar gum; nevertheless, PAM outperforms these alternatives in thickening capacity and crack resistance.
V. Safety Instructions & Storage Requirements
- Safety: Non-toxic and non-corrosive. Avoid inhalation of fine powder; wash hands thoroughly after handling.
Storage: Keep sealed in cool, dry and ventilated environment with a 24-month shelf life; protect from moisture and lump formation.