For professionals in the mortar, putty, and tile adhesive industry, redispersible polymer powder (RDP) is undoubtedly the core soul of dry-mix products.
However, most practitioners only focus on powder content, price, and fineness while ignoring the most critical indicator — Tg (Glass Transition Temperature). This parameter directly determines whether the mortar will crack, chalk, peel off, or fail in low-temperature construction.
Most common on-site problems such as chalking in winter construction, exterior wall cracking, tile hollowing, and soft dusty floors are not caused by incorrect formula ratios. In most cases, they result from inproper Tg of RDP.
This article explains the practical definition, on-site performance, and industry selection of Tg to give some reference for the people in construction industry.
What Is Tg (Glass Transition Temperature)?
Tg is the critical temperature point where the polymer film switches from a flexible rubber state to a hard brittle glass state.
Ambient Temperature ＞ Tg: The polymer film is soft, elastic, and stretchable. It can deform appropriately to resist temperature changes and prevent cracking.
Ambient Temperature ＜ Tg: The polymer film becomes hard, rigid, and brittle. It loses flexibility, cracks easily under slight stress, and tends to chalk and lose strength.
Tg is closely related to MFFT (Minimum Film Forming Temperature), another key indicator of RDP.
In short, Tg determines theflexibility and hardness of cured mortar, while MFFT determines the low-temperature construction adaptability.
On-Site Performance of Different Tg Values (Practical Case Analysis)
Low Tg (-10°C ~ 0°C): Outstanding Flexibility, Crack Resistance and Low-Temperature Resistance
RDP with low Tg forms highly elastic polymer films. Its biggest advantage is flexible deformation following the expansion and contraction of wall substrates.
Field Performance:
Exterior wall anti-crack mortar & plastering mortar: It effectively buffers structural stress caused by large temperature differences between day and night and seasonal changes, avoiding mesh cracks and surface crazing on exterior walls.
Low-temperature winter construction: It can form continuous and dense polymer films even at around 0°C, ensuring no chalking, no peeling, and stable final strength.
Exterior wall tile adhesive: For large-format tiles, heavy stones and exterior wall cladding, the flexible film adapts to thermal expansion and contraction, preventing hollowing and tile falling off.
Disadvantage: Excessively low Tg leads to overly soft films. It is not suitable for floor mortar, as the surface will be soft, easy to scratch, and poor in stain resistance.
High Tg (10°C ~ 15°C): High Hardness, Strength and Wear Resistance
High-Tg RDP forms rigid, compact and high-strength polymer films after film formation, focusing on structural hardness and compression resistance.
Field Performance:
Self-leveling mortar & floor screed: The cured floor features high hardness, excellent wear resistance and compression resistance, avoiding indentation, dusting and deformation under pedestrian and light vehicle load.
High-strength interior plastering mortar: The surface is firm, impact-resistant and non-dusting with excellent forming effect.
Disadvantage: High brittleness and poor flexibility. When used for exterior wall products, temperature fluctuations will easily cause cracking. It fails to form complete films in low-temperature winter construction, resulting in severe strength loss.
Medium Tg (0°C ~ 10°C): Balanced Performance & Universal Applicability
Medium-Tg RDP balances hardness and flexibility with moderate rigidity and toughness. It is the most stable and cost-effective choice for most interior putty and conventional plastering mortars.
Professional Tg Selection Standards for Common Mortar Products
Many manufacturers face frequent quality problems due to using a single type of RDP for all formulas. Different application scenarios require targeted Tg matching. The mature industry selection standards are as follows:
Exterior Wall Insulation Plaster & Anti-Crack Mortar (Low Tg Required)
Recommended Tg: -8°C ~ 0°C
Exterior walls suffer from the largest temperature difference and highest cracking risk. Priority should be given to flexibility. Low-Tg polymer films offset the expansion and contraction stress of substrates, ensuring stable performance throughout the year and eliminating common cracking defects.
Tile Adhesive & Grout & Exterior Wall Bonding Mortar
Ordinary interior tiles: 0°C ~ 5°C
Large/heavy/exterior wall tiles: -5°C ~ 0°C
The main failure of tile bonding is not insufficient adhesion, but bonding layer cracking caused by thermal expansion and contraction. Moderate flexibility effectively avoids hollowing, tile falling and grout cracking.
Self-Leveling & Floor Screed & High-Strength Floor Mortar (High Tg Required)
Recommended Tg: 10°C ~ 15°C
Floor products require high hardness, wear resistance and compression resistance. High-Tg RDP forms dense and rigid films, ensuring no deformation, no dusting and durable load resistance.
Interior Putty & Ordinary Plastering Mortar
Recommended Tg: 5°C ~ 10°C
Indoor environments have stable temperature with low cracking risk. Medium Tg balances surface fineness, construction performance and hardness, achieving the best cost performance.
Interface Agent & Repair Mortar
Recommended Tg: -5°C ~ 5°C
These products require both strong bonding force and appropriate flexibility. It can firmly bond new and old concrete substrates and resist shrinkage cracking after repair construction.
Three Common Tg Selection Misunderstandings in the Industry
Misunderstanding 1: The lower the Tg, the better
Excessively low Tg maximizes flexibility but significantly reduces hardness and wear resistance. The finished product will be soft, easy to absorb dust and stain, which is completely unsuitable for floor mortar.
Misunderstanding 2: The higher the Tg, the better
High Tg only applies to rigid floor products. Using high-Tg RDP for exterior wall mortar or tile adhesive will lead to high brittleness, poor crack resistance and total failure in winter construction.
Misunderstanding 3: One RDP model fits all formulas
This cost-saving mindset causes the most losses. Different scenarios have completely opposite performance requirements. Universal matching leads to frequent on-site quality failures, and the after-sales cost far exceeds the raw material price difference.
Longou produces redispersible polymer powder with different Tg values to be used in various applications. We also provide technical support. If you have problems with your drymix mortar products, please feel free to contact our team. Our technical team will provide suitable solutions based on your problems.
Post time: May-29-2026