Gypsum Retarder

Gypsum retarder is a chemical additive designed to delay the setting time of gypsum, primarily employed in gypsum-based building materials to control the rate of gypsum hydration. These products are typically supplied in powder form, readily soluble in water, and deliver effective retarding properties even at low dosage rates.

Advantage & Benefits

Amino acid-based retarders exemplified by GR90, synthesised using multiple amino acid technologies, offer five core advantages:

1. Strength Stability: Minimal impact on dihydrate gypsum crystal morphology, with hardened body flexural/compressive strength loss rate <5%, significantly outperforming citric acid (which can reach 30% loss rate);
2. Precise Controllable Retarding Efficiency: At 0.1% dosage, setting time extends to over six times that of the blank sample, with linear adjustment according to dosage;
3. High Compatibility: Suitable for diverse substrates including natural gypsum, desulphurisation gypsum, and phosphogypsum; exhibits excellent synergy with admixtures such as water-reducing agents and cellulose ethers;
4. Construction-Friendly: Light yellow powder dissolves readily in water with superior dispersibility, achieving uniform dispersion through direct mixing;
5. Environmentally Sound & Safe: Free from chlorides and heavy metals; pH neutral (6-8), compliant with green building material standards.

Gypsum retarders are extensively utilised in various gypsum-based building materials, primarily including:

• Gypsum Board Production: Gypsum boards, fibreboards, partition boards, ceiling panels, etc.
• Gypsum Plastering Materials: Plastering gypsum, rendering gypsum, machine-applied spray plaster, etc.
• Gypsum Blocks and Precast Elements: Gypsum blocks, gypsum panels, gypsum flues, etc.
• Specialised Applications: Gypsum-based self-levelling screeds, dental/medical gypsum, ceramic manufacturing, etc.
• Decorative Gypsum Products: Gypsum decorative coatings, gypsum fillers, jointing compounds, etc.

Based on their mechanism of action and chemical composition, mainstream retarding agents are categorised into three types:

1. Organic acids and their soluble salts (e.g., citric acid, tartaric acid, sodium gluconate)
Characteristics: Significant setting retardation achievable at low dosages (0.03%-0.1%). Citric acid exhibits high retardation efficiency but substantial strength loss (compressive strength declines sharply at dosages >0.05%);
Suitable applications: Ordinary gypsum-based putty or joint fillers requiring extended working time with controllable strength loss.

2. Inorganic phosphates (e.g., sodium hexametaphosphate, sodium polyphosphate)
Characteristics: Moderate retarding effect with strength loss lower than citric acid but higher than borax; dosage must be controlled (0.05%-0.2%);
Suitable applications: Gypsum blocks, precast panels, and other products requiring moderate strength.

3. Amino acid synthesis derivatives
Characteristics: Utilises the unique molecular structure of amino acids to adsorb gypsum particles and delay hydration. Key advantages include retarding setting time with minimal strength loss, alongside being environmentally friendly and non-toxic. Representative products such as GR-90 can flexibly adjust setting time with a dosage of 0.02%-0.3%.