Factory Test Analysis of the Influence of Redispersible Polymer Powder Addition on the Shrinkage Rate of Plastering Mortar

Shrinkage is an important performance consideration in plastering mortar. Excessive dimensional 

change during drying can contribute to surface cracking and affect the bond between mortar and 

substrate. For formulators, evaluating the effect of redispersible polymer powder (RDP) addition

can help optimize mortar performance.

How RDP Addition Affects Plastering Mortar

Redispersible polymer powder is widely used in dry mix mortar to improve key properties such 

as bonding strength and flexibility. After mixing with water, the polymer redistributes within the

mortar and forms a polymer film during drying.

In plastering mortar, these properties can help the hardened mortar better accommodate internal

stress and movement. However, shrinkage does not depend on RDP alone. Cement content,

aggregate grading, water demand, substrate, curing conditions, and the overall formulation can all

affect the final result.

Therefore, RDP dosage should be evaluated as part of the complete plastering mortar formulation.

Factory Test: Evaluating RDP Addition

The factory test described in this article compared plastering mortar formulations with different RDP

addition levels and evaluated their shrinkage performance.

The original test reported improved shrinkage performance when RDP was added at a 2% level. 

However, this result should be treated as formulation-specific rather than as a universal recommen-

ded dosage. The optimum RDP level depends on the mortar composition and required performance.

For a more reliable formulation study, compare a reference formulation with several RDP dosage

levels while keeping other raw materials and testing conditions consistent.

Key properties to monitor include:

- Drying shrinkage: Measure dimensional change over a defined curing period.

- Bonding strength: Evaluate adhesion to the intended substrate.

- Flexibility: Check whether the modified mortar can better accommodate deformation.

- Surface cracking: Record visible cracks under controlled drying conditions.

- Workability: Confirm that RDP addition does not negatively affect application properties.

Testing several dosage levels is generally more useful than assuming that a fixed percentage will 

provide the same result in every formulation.

How to Select RDP for Plastering Mortar

RDP selection should start with the performance requirements of the mortar.

If the formulation requires higher bonding strength together with flexibility, JINT™-502 and JINT™-740 

are suitable candidates for comparative formulation trials. Both products are described on the official 

product pages as RDP grades with high bonding strength and functions including bonding strength 

and flexibility.

If the formulation needs a universal-grade RDP with basic bonding and flexibility properties, JINT™-503

can be evaluated as another option. Its official product page describes it as a universal-grade RDP for

dry mix mortars, with bonding strength and flexibility.

For plastering mortar, the final choice should be based on comparative test results rather than product

grade alone

Practical Testing Recommendation

A simple screening program can use the same cement, aggregates, water, substrate, and curing cond-

itions while varying only the RDP type or dosage.

Compare shrinkage together with bonding strength, flexibility, and workability. If a formulation shows

lower shrinkage but insufficient bonding or unsuitable workability, adjust the complete formulation

instead of simply increasing the RDP dosage.

This approach helps identify an RDP level that provides the required balance between performance

and formulation cost.

Conclusion

The influence of RDP on plastering mortar shrinkage should be evaluated through controlled formulation

testing. RDP can contribute bonding strength and flexibility, but the final shrinkage performance depends

on the complete mortar system.

For formulators and buyers, the practical approach is to define the required performance, select appropriate

RDP candidates, and verify their effect through comparative laboratory or factory trials.

For RDP options for dry mix mortar applications, see the RDP Redispersible Polymer Powder product range

from JINTEDIFU.

Name: Zane Liu

E-mail: zane.liu@jtdf-rdp.com

Phone: +86 166 5317 6310（WhatsApp）